Spiranthes delitescens - Sheviak
Canelo Hills Ladies'-tresses
Other Common Names: reclusive ladies'-tresses
Taxonomic Status: Accepted
Related ITIS Name(s): Spiranthes delitescens Sheviak (TSN 507181)
Unique Identifier: ELEMENT_GLOBAL.2.138772
Element Code: PMORC2B140
Informal Taxonomy: Plants, Vascular - Flowering Plants - Orchid Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Monocotyledoneae Orchidales Orchidaceae Spiranthes
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Concept Reference
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Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Spiranthes delitescens
Taxonomic Comments: Spiranthes plants of southern Arizona, initially classified as Spiranthes graminea, are now considered to be a distinct species, S. delitescens, based on morphological and cytological differences (Sheviak 1990).

Classification of members of the Spiranthes genus is difficult due to the frequent inter-specific hybridization of this genus (Luer 1975). Interestingly, two new species of Spiranthes, in addition to S. delitescens, have been identified since 1984. One of these is Spiranthes diluvialis of Colorado and Utah, which had been misidentified as both S. romanzoffiana and S. cernua (Sheviak 1984), and the other, more recently identified and similar to the southern Arizona plants, had been classified as S. graminea but later was determined to be a new species, Spiranthes nebulorum, which grows in Mexico and Guatemala (Catling and Catling 1988).

Confusion over the taxonomic standing of the southern Arizona orchid is due to the similarity of the characteristics of this species with the Central American S. graminea and the northern S. diluvialis, as well as with several other species of Spiranthes (Luer 1975; Sheviak 1990; Mason pers. comm.; van Devender pers. comm.). Due to cytological and morphological differences between the southern Arizona plants and other Spiranthes species, Sheviak (1990) determined that the Spiranthes of one southern Arizona site and the three neighboring marshes were a new distinct species. The identity of the parents of this hybrid species is not known. However, the haploid chromosome number of 37, similar to S. diluvialis, suggests that the two parents had differing chromosome numbers of 22 and 15 (Sheviak 1990), since two cytological series of Spiranthes exist: a smaller group with a base of 22 chromosomes and a larger number of species with a base of 15 chromosomes. Only three western North American species in the 22-series exist: S. romanzoffiana, S. Porrifolia and S. magnicamporum (Sheviak 1990). The floral shape is similar between S. porrifolia and the southern Arizona species, thus supporting the hypothesis that the southern Arizona plants originated from S. porrifolia (Sheviak 1990). The similarity in pubescence of S. vernalis and the southern Arizona plants suggest the possibility of this species being the 15 base chromosome parent (Sheviak 1990).
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 10Aug2014
Global Status Last Changed: 19Dec2011
Ranking Methodology Used: Ranked by calculator
Rounded Global Status: G1 - Critically Imperiled
Reasons: Known only from 4 mid-level wetland locations southern Arizona. Cienega habitat is extremely limited in this mostly arid region and other suitable locations in Arizona and Sonora, Mexico have been thoroughly searched without success. Most cienega habitat has been lost, seriously degraded, or is in danger of being destroyed due to growing water demands and associated diversions and impoundments, uncontrolled livestock grazing, the introduction of invasive exotic plant species, sand and gravel mining, and other threats. Many of these ecosystems have not yet recovered from the widespread erosion and channel entrenchment that resulted from poor management practices of over a century ago. Spiranthes delitescens is particularly threatened by the growth of dense vegetation around it (AFGD 2000).
Nation: United States
National Status: N1

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Arizona (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (06Jan1997)
U.S. Fish & Wildlife Service Lead Region: R2 - Southwest

NatureServe Global Conservation Status Factors

Range Extent Comments: Four populations of Spiranthes delitescens have been found in Arizona ranging over 8 sq km. Their range includes Cochise County - Babocomari Cienega, Santa Cruz County - along Turkey Creek, at Canello Hills Cienega along O'Donnell creek, and on a slope below Sheehy Spring (Sheviak 1990).

According to Sheviak (1990), this species most likely exists in Mexico, however to date, no plants have been located south of Arizona. The occurrence of other populations of this species of Ladies' Tresses in the United States, is probably unlikely due to the limited available locations possessing the specific habitat parameters which appear to be required by these plants (Sheviak 1990).

Area of Occupancy: 3-5 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 1 - 5
Number of Occurrences Comments: Four element occurrences. Two occurrences have not had their population status formerly updated since 1980 and 1981, though an informal survey at one site in 1999 turned up the largest individual count of this species. The other two element occurrences have not been observed since 1995 and 1998. This species is in need of a status survey.

Population Size Comments: Only one population is monitored yearly and populations vary greatly from year to year, so numbers could be higher.

Because most southern Arizona cienegas have been thoroughly searched, the possibility of locating new populations in the state is low. However, habitat in New Mexico and Mexico needs to be surveyed. (USFWS 2001).

Number of Occurrences with Good Viability/Integrity: Very few (1-3)
Viability/Integrity Comments: The last known viability assessment was 'good' for the occurrence on the TNC Canelo Hills Cienega Preserve.

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: The foreseeable threat with the greatest impact is habitat degradation/loss. This species is threatened by competition from native and non-native invasive plants. According to the Arizona Fish and Game Department (2000), "possibly the greatest threat to the survivability and fecundity of the orchid is the dense vegetation surrounding the small orchid plants." The invasion of the exotic Johnson grass (Sorghum halepense) into the Canelo Hills Cienega and the aggressive growth of Equisetum spp. may exacerbate the problem (The Nature Conservancy Arizona Field Office, pers. comm.). Sedges and cattail may also compete with the orchid by forming mats that the orchid cannot grow through (AFGD 2000). McClaran and Sundt (1992) speculate that competition from neighboring plants for nutrients and sunlight may decrease the photosynthetic rate and the vigor of the Spiranthes. In addition, the lowered temperature and elevated moisture level of the soil may alter the growth rate of the orchid; more likely, this would directly affect the fungi-orchid association. Presumably (inferred from information on other terrestrial species), germination will not occur if the environmental conditions are not sufficient for mycorrhizal penetration into the newly dispersed seeds. Possibly, a specific environmental cue, such as high light intensity, is required to trigger a greater percentage of flowering plants than has been seen in recent years.

Changes in the habitat in which an orchid is growing may be lethal, tolerable or beneficial to the survival of the plants, depending on the species of orchid. The alteration of the community structure may help maintain the specific parameters of the site required by the particular orchid species (Sanford 1974; Sheviak 1974; Dressler 1981). Species that tolerate disturbances may rely upon their saprophytic capabilities and, as long as the environmental conditions necessary for the fungi-orchid association are present, the plant may remain underground until the above-ground conditions are favorable for growth (Stoutamire 1974; Wells 1981).

Many orchid species cannot compete with fast growing, large herbaceous plants. The population size of Spiranthes growing in areas where land is frequently disturbed (mowed, plowed, etc.) decreases when tall grasses or dense short grasses increase in abundance (Sanford 1974). There is evidence that Spiranthes delitescens requires some disturbance (AFGD 2000).

Other threats to Spiranthes delitescens include growing water demands and associated diversions and impoundments, uncontrolled livestock grazing as well as lack of grazing, sand and gravel mining, collection, and possibly fire suppression (AFGD 2000).

Short-term Trend: Unknown
Short-term Trend Comments: The Nature Conservancy has monitored the plants at its reserve since 1979, and has made yearly counts of the total population since 1993 (AGFD 2000). There is not a clear trend in the data because the total number of plants varies greatly from year to year due to environmental factors such as mat buildup of cattails and sedges which plants have a hard time penetrating (AGFD 2000).

The total number of plants at the Canelo Hills Cienega Preserve was as high as 521 in 1995 and as low as 19 in 1997 (AGFD 2000). Only one plant bloomed in 1997, but 107 plants bloomed in 1995 (AGFD 2000). An informal survey of the population in San Rafael Valley, turned up 731 blooming plants which is the largest colony of S. delitescens known (AGFD 2000).

Long-term Trend: Decline of 30-50%
Long-term Trend Comments: Suspected.

Intrinsic Vulnerability Comments: Perennial deciduous mycotrophic plant, dependent upon mycorrhizal relationship with fungus for part or all of its nourishment. Totally parasitic upon fungus for germination and early growth stages.

Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.
Environmental Specificity Comments: Marshy wetland or cienega intermixed with tall grasses and sedges. Grows on slope near water so soil is drained although saturated. As slope increases, growth increases. There is some, but incomplete, evidence that burning helps maintain the orchid population, probably by eliminating the buildup of thatch which the small orchid plants cannot penetrate (Coleman 1999 cited by AGFD 2000). Substrate: Finely grained, highly organic, saturated soils.

Other NatureServe Conservation Status Information

Distribution
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Global Range: Four populations of Spiranthes delitescens have been found in Arizona ranging over 8 sq km. Their range includes Cochise County - Babocomari Cienega, Santa Cruz County - along Turkey Creek, at Canello Hills Cienega along O'Donnell creek, and on a slope below Sheehy Spring (Sheviak 1990).

According to Sheviak (1990), this species most likely exists in Mexico, however to date, no plants have been located south of Arizona. The occurrence of other populations of this species of Ladies' Tresses in the United States, is probably unlikely due to the limited available locations possessing the specific habitat parameters which appear to be required by these plants (Sheviak 1990).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map

U.S. & Canada State/Province Distribution
United States AZ

Range Map
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U.S. Distribution by County Help
State County Name (FIPS Code)
AZ Santa Cruz (04023)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
15 Upper San Pedro (15050202)+, Upper Santa Cruz (15050301)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A slender herb with grass-like leaves and an erect flowering stalk that reaches about 5 dm in height. Perennial but plants may have no above-ground structures in some years. Up to 40 small white flowers may bloom on the end of each flowering stalk.
General Description: Spiranthes delitescens is a slender, erect, terrestrial orchid which, when in bloom, reaches approximately 50 cm tall. Five to ten, linear-lanceolate, grass-like leaves, 18 cm long and 1.5 cm wide, grow basally on the stem. The fleshy, swollen roots are approximately 5 mm in diameter. The twisted spike inflorescence may contain up to 40 white flowers. The tubular flowers consist of wide-spreading lateral sepals and linear petals, with a 6 mm to 8 mm long, pleated lip. The column is slender and the rostellum elongate and deeply bifid (Luer 1975; McClaran and Sundt 1992; Sheviak 1990).
Diagnostic Characteristics: Spiranthes delitescens can be distinguished from other Mexican and southwestern United States Spiranthes species by the shape of its medium-sized flowers: the floral tube curving into a horizontal apex and an ascending base, and the sepals curving outward and downward. In addition, the pubescence is distinct; the trichomes are glandular-capitate and taper at the apex. Cytological differences between S. delitescens and other Spiranthes species also exist (Sheviak 1990).
Duration: PERENNIAL
Reproduction Comments: Flowers, Pollination and Hybridization: Orchid flowers have a unique morphology which has coevolved with their pollinators (van der Pijl and Dodson 1966). A large petal, called the labellum or lip, acts as a landing platform for many pollinators. In Spiranthes spp., balls of sticky pollen grains, pollinia, are positioned near the column (the partially united stamen and pistil) in such a way that when the pollinator enters the floral tube, on its way to the nectaries, it inadvertently triggers the rostellum causing the pollinia to be deposited on the pollinator (van der Pijl and Dodson 1966). Bees are the primary pollinator for Spiranthes, with Bombus being the most common genus; other pollinating organisms include flies, moths, and butterflies (van der Pijl and Dodson 1966; Dressler 1981). Within three days of successful pollination, Spiranthes flowers dehydrate and become discolored (Catling 1982).

One pollinia contains over 10,000 pollen grains. This allows for efficient fertilization of the thousands of ovules in the ovaries of most orchids (van der Pijl and Dodson 1966). Some orchids are self-fertile, but most often fertilization is the result of outcrossing. Self-pollination is advantageous when plants have extended their range into areas not previously inhabited by the species (Dressler 1981). Spiranthes are often self-fertilized, and individuals that require cross-pollination are receptive for only 10 to 40 days (Catling 1982). Flowers older than 40 days contain dead ovules (Catling 1982). Within three weeks of pollination the seeds are fully developed and the ovary splits. Usually 100% of Spiranthes ovaries expand, but often only 50% of them contain seeds (Catling 1982). Orchids easily hybridize; both inter-specific and inter-generic hybrids occur in the wild (Sanford 1974).

In dry climates, flowering often occurs during the rainy season. Flowering of the Spiranthes occurs in July, when temperatures range from 60 F at night to 100 F during the day and when the majority of the year's 15 to 20 inches of precipitation falls (Merrigan 1990; The Nature Conservancy Arizona Field Office, pers. comm.). In some cases too much rain, possibly causing a decrease in pollinator activity, results in a decrease in the number of flowers and consequently the number of fruits (Dressler 1981). Most nontropical species release their seeds in the fall at the beginning of the dormant period (Dressler 1981). In addition to moisture dependency, flowering of some species of Spiranthes is photoperiodically induced (Catling 1982).

The age of sexual maturity is dependent on the species and can range from several years to over twenty years (Stoutamire 1974; B. Jennings, pers. comm. 25 Jan. 1990). Inflorescences first develop in Spiranthes spiralis thirteen to fifteen years after seed germination (Wells 1981). Once reproductively mature, the age of the plant is not a factor in flowering, whereas temperature and precipitation appear to be significantly related to the percentage of flowering plants (Wells 1981). Spiranthes diluvialis will not bloom in dry years when precipitation levels are atypically low (B. Jennings, pers. comm. 25 Jan. 1990). S. spiralis plants which have reverted back to the saprophytic stage are capable of flowering during the initial year of resuming above-ground growth (Wells 1967). The average percentage of flowering S. spiralis plants over a thirteen year period was 33, ranging from 73% in 1966, 19% in 1970, 43% in 1973, down to 1% after the 1976 drought, and recovering to 31% the following year (Wells 1981).

Ecology Comments: SPIRANTHES OF CANELO HILLS CIENEGA AND TURKEY CREEK: The grass-like leaves of the orchid, growing low in the sedge and horsetail fields, are difficult to see for most of the year. The inconspicuous plants are visible July and August when the roughly 20 cm tall inflorescences develop (P. Sundt, pers. comm. 23 Jan. 1990; The Nature Conservancy Arizona Field Office, pers. comm.). The fruits mature approximately three weeks after the flowers form, usually during the end of August, releasing hundreds of tiny seeds from each capsule to be dispersed, probably via the wind (McClaran and Sundt 1992; P. Sundt, pers. comm. 23 Jan. 1990). Many inflorescences are damaged during the summer; Sundt (pers. comm. 23 Jan. 1990) feels that grasshoppers may be responsible for the broken stalks and the chewed capsules.

The life-cycle of the plants is unclear. Most likely these orchids are perennial; however, no dormant underground structures have been identified (McClaran and Sundt 1992). Determining the over-wintering structure is difficult without disturbing the plants. The plant may remain below-ground most of the year or, common to many Spiranthes, small, inconspicuous leaf rosettes may grow throughout the cool months, hidden by the tall vegetation (McClaran and Sundt 1992; B. Jennings, pers. comm. 25 Jan. 1990). In February, an inspection of approximately 40 flagged areas (presumably indicating the previous year's orchids) revealed no above-ground orchid structures (Newman 1990). Plants rarely flower in consecutive years and the relationship between the flowering plants cannot be elucidated since the growth pattern of the subterranean structures is unknown (McClaran and Sundt 1992).

Censuring of the Spiranthes at Canelo Hills began in 1978; however, accurate assessment of the demographic patterns is difficult because varying techniques were used during the first eight years of monitoring. With this caveat in mind, the total number of plants in O'Donnell Canyon fluctuated from 40 in 1978, 196 in 1979, dropping to 30 in 1982 through 1984, and then increasing to roughly 80 plants in 1988 (McClaran and Sundt 1992). This data suggests that the number of flowering plants has declined since 1979. Few conclusions can be drawn from the data, considering that the early measurements were based on the number of flowering plants and the later censuring was based on the total number of plants (flowering and not flowering), and that individual plants would appear one year, not appear the following year (no visible above-ground structures), and then reappear in subsequent years. In fact, it is difficult to estimate population size based on counts of aboveground plants due to the lack of information concerning the life-cycle and environmental requirements of Spiranthes delitescens. Other species of Spiranthes grow initially underground saprophytically for many years, revert back to saprophytic growth when environmental conditions are not favorable and flower irregularly. Population declines followed by recoveries are characteristic of many Spiranthes.

The plants growing at Turkey Creek appear to be in a plant community characterized by shorter plant height and greater alpha diversity than at Canelo Cienega. Grazers have been excluded from the latter location since 1969, when this part of Canelo Hills was bought by The Nature Conservancy; Turkey Creek is currently grazed (McClaran and Sundt 1992; P. Sundt, pers. comm. 23 Jan. 1990). Thus, although soils and topography of the two sites differ, grazing is also a likely factor differentiating the two sites.

The population in Turkey Creek, ranging from hundreds to thousands of plants, appears healthier and more vigorous than the Canelo Hills' population (McClaran and Sundt 1992; M. Heitlinger, pers. comm. 8 Jan. 1990; P. Warren, pers. comm. 25 Jan. 1990). Sundt (pers. comm. 23 Jan. 1990) proposes that the Turkey Creek plants have always been more vigorous than the O'Donnell Creek plants, due to the different characteristics of the particular sites, and that little significant change has occurred in the two populations over time.

SPIRANTHES AND OTHER TERRESTRIAL ORCHIDS

Seeds and Fruits: Terrestrial orchid fruit are usually thin-walled, dry, and papery (Dressler 1981). Depending upon the species, Spiranthes fruit may mature within a few days after fertilization or may take as long as one year to completely develop (Luer 1975). Seeds of terrestrial orchids tend to mature and are dispersed at the end of the plants' growing season, which often coincides with the time of maximum germination (Stoutamire 1974). When fully mature, the valves on the capsule open and the wind-borne seeds are dispersed (Luer 1975). Water and humans have also been implicated in orchid seed dispersal; there is no evidence supporting the involvement of non-human animals (Sanford 1974). Orchid seeds have been found 400 miles from the parent plant; without human intervention, however, dispersal rarely occurs this far (Sanford 1974).

Orchid seeds are rudimentary when dispersed; the sole protection of the undifferentiated embryo is the seed coat, and no endosperm or other form of nourishment surrounds the embryonic plant (Luer 1975; B. Jennings, pers. comm. 25 Jan. 1990). Due to the naked, unprotected seed structure a dormancy period is highly unlikely and the period of viability relatively short (Stoutamire 1974; B. Jennings, pers. comm. 25 Jan. 1990). The rapid dispersal, lack of dormancy, requirement for specific fungi, and necessity of precise environmental conditions explains the extremely low seed survival rate of an estimated one in a million (Stoutamire 1974; Luer 1975; B. Jennings, pers. comm. 25 Jan. 1990).

Cultivated Orchids: Terrestrial orchids are difficult to grow due to the specific symbiotic associations often required. Dimmitt (pers. comm. 22 Jan. 1990) does not know of any amateur orchidist having successfully germinated and cultivated any member of the genus Spiranthes. Although limited, laboratory and greenhouse experiments have uncovered some information on the germination and growth of terrestrial orchids. The seeds of many Spiranthes species retain their viability for three years when stored in a refrigerator (Stoutamire 1974). Spiranthes cernua seeds germinate readily in sterile water; S. orchioides seeds swell with inhibition but fail to germinate (Stoutamire 1974).

When placed under a light source after germination, several Spiranthes species produce chlorophyll; this indicates an ability to grow autotrophically in the absence of a mycorrhizal associate. However, other species require sterile agar media, containing mineral salts and an external source of organic carbon, indicating an obligate heterotrophic (required mycorrhizal associates) stage (Stoutamire 1974; Dressler 1981; Arditti 1982). Arditti (1982) lists the specific media requirements for laboratory growth of many Spiranthes species. No information is available about the early growth requirements of S. porrifolia and S. vernalis, the putative parents of the southern Arizona plants. When plants are grown in sterile laboratory conditions, light is required for normal development of many early photosynthesizing species, but it may inhibit the germination of the late-photosynthesizing species (Stoutamire 1974).

A protocorm develops from the undifferentiated embryo and is the initial external structure when seed germination commences (Sanford 1974; Stoutamire 1974). Two stages of high mortality are found in agar-grown seedlings: the first stage occurs shortly after the protocorm emerges from the seed coat, when it reaches 1 mm to 2 mm in length, and the second stage occurs shortly after the roots develop. In the wild this later stage correlates with the transitional period when the seedling changes from an obligate mycorrhizal dependent to a partly autotrophic organism (Stoutamire 1974).

In the lab, seedling growth initially occurs in the downward direction and after several centimeters of growth the apical meristem turns and grows upward (Stoutamire 1974); in Spiranthes the protocorm initially forms into the tubercle (Sanford 1974). During the first year of growth, short thickened corms or modified lateral buds, called sinkers, are formed in most terrestrial orchids (Stoutamire 1974). Spiranthes spiralis development is expedited by laboratory conditions and within 18 months after the seeds are sown, four green leaves and a 5 mm long tuber are produced (Wells 1981). Enlarged primary structures develop concurrently with the first seedling leaves. Adventitious buds on the stem of some Spiranthes species are capable of vegetative reproduction (Stoutamire 1974). In the greenhouse, S. cernua and S. sinensis develop from a protocorm to a flowering plant in 35 months and 29 months, respectively (Stoutamire 1974).

Germination and Mycorrhizal Associations: Mycorrhizal penetration into the seed and embryo is required for successful germination of most terrestrial orchid seeds; the seedlings are obligate mycorrhizal dependents until aerial shoots and photosynthesizing apparatuses have developed (Dressler 1981). The abundance of hair-like projections on the non-photosynthesizing protocorms may allow for rapid mycorrhizal association (Stoutamire 1974). Results from laboratory studies suggest a more rapid germination and development period in the early photosynthesizing species than in the late photosynthesizing species, possibly due to a facultative, rather than obligate, relationship of the former species with the fungus (Stoutamire 1974). Most often chlorophyll does not develop for several months even in the early photosynthesizing species (Dressler 1981). Wells' (1981) results indicate that juvenile orchids remain underground and thus without chlorophyll for greater than one year and maybe as long as fifteen years. As the plant ages, the dependency on fungi is reduced; however, most mature terrestrial orchid roots are associated with endophytic fungi (Warcup 1975, Dressler 1981).

Most of the rapidly photosynthesizing protocorm species require sunlight to germinate and often grow in sunny wet areas, characteristic of open marshes and bogs (Stoutamire 1974; Dressler 1981). Whereas germination of most of the non-photosynthesizing protocorm species is inhibited by light, these species grow in well-drained forest soils or open, seasonally dry grasslands (Stoutamire 1974; Dressler 1981). Thus species that grow in cienegas, such as the southern Arizona plants, are presumably early photosynthesizers.

Mycorrhizal fungi are required to supply the embryo with needed enzymes and nutrients early in the growth of the seedling; minerals, vitamins and an available organic carbon source are essential to the development of the plant (Stoutamire 1974; Luer 1975; Dressler 1981). The species-specificity of the fungi-orchid symbiosis is ambiguous and is thought to decrease as the plant ages (Warcup 1975). The association with a Basidiomycete fungi is thought to range from 1 to 15 years before the first leaf emerges (McClaran and Sundt 1992). Several different species of fungi are associated with most roots, and taxonomic relationships between fungi and orchid species appear to exist (Warcup 1975; Dressler 1981). Environmental conditions will affect the fungi-orchid relationship; high levels of nitrogen and low soil pH may reduce the likelihood of fungal penetration into the seed, thus decreasing the germination rate (Warcup 1975).

The absence of visible growth of an orchid plant does not imply dormancy or death of the plant (Stoutamire 1974). Often orchids grow below-ground for several years without emerging from the soil, receiving nourishment from fungal assimilates (Stoutamire 1974). Some terrestrial orchids have grown saprophytically and remained underground for fifteen years (Sanford 1974). Spiranthes spiralis grows saprophytically, solely as a mycorrhizal-rhizome type structure, for eight years before a tuber is produced and a total of eleven years before aerial stems are produced (Wells 1981).

Vegetative Growth and Population Fluctuations: Orchids may grow vegetatively for many years before flowering. Cypripedium candidum requires more than twelve years to reach reproductive maturity (Bender 1986) and some Spiranthes only bloom every twenty years (B. Jennings, pers. comm. 25 Jan. 1990). Underground structures include tubers, corms, sinkers, roots, and storage roots (Stoutamire 1974). Vegetative propagation occurs through the growth of buds on lateral underground stems, and newly formed plants eventually separate from the parent plant (Wells 1967). Orchids do not produce typical primary roots and most growth occurs in the secondary root system (Stoutamire 1974). The roots of most terrestrial orchids which grow in moist areas occur above the water-line, allowing for the provision of sufficient amounts of oxygen (Dressler 1981). Depending on the species, above-ground vegetative growth may continue year-round or only during the warm growing season. The normally slow growth rate often decreases in the cool season and small over-wintering leaf rosettes may form (B. Jennings, pers. comm. 25 Jan. 1990).

Spiranthes spiralis, growing in the grasslands of England, are green year-round; leaf rosettes are present when the plants are not in bloom (Wells 1981). In January, a mature plant will contain two mature tubers produced the previous year and a small protuberance, which will develop into the following year's tuber. Plants of this species produce no roots, thus the tuber and fungi are responsible for obtaining the necessary nutrients and water. In July the leaf rosettes die and by August new leaves are formed and a flowering stalk develops (Wells 1981).

Stable communities, with a relatively fixed number of mature plants, often have high seedling mortality (Stoutamire 1974). However, terrestrial orchid populations often display great fluctuation within several year periods (Luer 1975). Colonies of many Spiranthes species are often labile and above-ground parts may appear and disappear in alternating years (Luer 1975). Population size can alternate from several to hundreds to thousands and back down to several plants in a few years (B. Jennings, pers. comm. 25 Jan. 1990). Plants of Spiranthes diluvialis in one location fluctuated from 5500 visible flowering plants in 1986 to 200 plants in 1989, whereas another population, experiencing similar weather conditions and apparently no different management practices, did not have a large flux in population size (B. Jennings, pers. comm. 25 Jan. 1990). One population of Spiranthes spiralis went from 420 plants in 1963 to 1050 plants in 1969 (Wells 1981); however, the population size of Spiranthes spiralis usually remains relatively constant (Wells 1967).

Sheviak (1974) attributes the pronounced changes in population size and distribution to both climatic fluctuations and edaphic factors which influence the saprophytic/autotrophic state of the orchid. Due to the narrow pH tolerance, specific temperature and moisture requirements of the fungi-orchid association, changes in the environment will lead to altered states of the orchid (Sheviak 1974, B. Jennings, pers. comm. 25 Jan. 1990). In horticultural conditions, S. cernua and S. magnicamporum can revert from an autotrophic state to a saprophytic state (Sheviak 1974). Some orchids, such as Triphora trianthophora, grow underground saprophytically for most of their life and only occasionally produce aerial stems (Sheviak 1974). Habenaria leucophaea and some other very rare orchids, may produce hundreds of plants in a location where it was previously rare and then one or two seasons later disappear back to the saprophytic state where it remains for many years (Sheviak 1974).

The various negative slopes in the linear survivorship curves (number of plants versus survival years) of different Spiranthes spiralis cohorts (same age plants) indicate that the chance of survival is dependent on the year in which the cohorts were produced and is not significantly affected by varying environmental conditions (Wells 1981). The mean expected life for all the cohorts was 53 years and the calculated time until only one plant remained for each cohort ranged from 23 years to 67 years (Wells 1981).

Estuarine Habitat(s): Herbaceous wetland
Palustrine Habitat(s): Bog/fen, HERBACEOUS WETLAND, Riparian, TEMPORARY POOL
Terrestrial Habitat(s): Desert, Grassland/herbaceous, Woodland - Hardwood
Habitat Comments: [SUMMARY: Cienegas (mid-elevation wetland communities) at about 1525 m elevation. Soils are highly organic and seasonally or continuously water-saturated, but are not subject to scouring floods. Associated plants are mostly tall grasses, sedges, and rushes. END SUMMARY]

Most members of the genus Spiranthes require a moist habitat (B. Jennings, pers. comm. 25 Jan. 1990). S. graminea grows abundantly in cienegas (permanently wet meadows in desert foothills) and in the mountains of central Mexico (Luer 1975). Spiranthes diluvialis, in Colorado and Utah, grow in flood plains, old stream channels and along streambeds, in densely vegetated open sites and under willow trees (B. Jennings, pers. comm. 25 Jan. 1990).

The four populations of Spiranthes delitescens occur above a dam in Babocomari Cienega, in marshy meadows, seeps and hummocks along Turkey Creek, in marshy meadows and seeps at O'Donnell Cienega, and on a seeping slope below Sheehy Spring (Sheviak 1990).

The dominant vegetation in the cienegas near the Spiranthes include grasses, sedges (Carex spp.), rushes (Juncus spp.), spike-rush (Eleocharis spp.), cat-tails (Typha spp.), and horsetails (Equisetum spp.) (Grater 1973, Merrigan 1990, The Nature Conservancy Arizona Field Office, pers. comm.). Johnson grass (Sorghum halepense), a potential threat to the orchid, appears to be spreading into the marshy meadow (McClaran and Sundt 1992). The cienegas are at approximately 1500 m elevation and contain fine grained, highly organic, saturated soils (Merrigan 1990, The Nature Conservancy Arizona Field Office, pers. comm.). The orchid grows in both saturated soil and the surrounding drier sites.

Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: The population at one site, ranging from hundreds to thousands of plants, appears healthier and more vigorous than another one. Possibly the greatest threat to the survivability and fecundity of the orchid is the dense vegetation surrounding the small orchid plants. Possible effective management practices such as grazing, fires, and control of competing native and non-native plants have not been researched enough to determine the best practice or the best combination of practices. Due to the possible fluctuation in population size resulting from the reversion from a partially autotrophic plant back to a saprophytic plant, a characteristic common to many Spiranthes species, the status of these plants cannot be determined. Extensive research on the life-cycle and environmental requirements of this species is required before management plans should be discussed; burning experiments are being planned for one population.
Restoration Potential: Recovery of the Spiranthes is dependent on determining the optimum habitat conditions required for successful flowering, fruiting, germination, and maturation. Most probably this will relate to reduction in the density of the vegetation cover of the marsh. A prescribed burn at one protected site in 1991 failed to increase orchid numbers that year. But because saprophytic individuals in other Spiranthes species take at least one year to revert to aboveground plants and because germinated seeds must spend one to twelve years as obligate saprophytes, the response of the population to the prescribed burn is not known at this time. Therefore, until the ecological requirements are known and optimal conditions can be produced through management actions, we can only speculate as to the recovery potential of the populations.
Management Requirements: DISCUSSIONS ON NATURAL OCCURRENCE AND MANAGEMENT IMPLICATIONS OF FIRE AND GRAZING AT (TWO SITES) AND THE RESPONSE OF ORCHIDS TO HABITAT ALTERATIONS:

Heitlinger (pers. comm. 8 Jan. 1990) and McClaran (pers. comm. 24 Jan. 1990) feel that historically fires occurred naturally in the cienegas when lightning-caused fires in the uplands spread down into the marshes and burned at cool temperatures. Suppression activities and roads are factors resulting in the reduction of the spread of natural fires. Most likely the fires would have occurred in the late spring (April through June) before moist, green vegetation developed (Merrigan 1990). In this case, fires would have periodically removed the dense vegetation surrounding the orchids prior to maximum orchid growth. However, Gehlbach (1986) and Sundt (pers. comm. 23 Jan. 1990) feel that little evidence exists to support the assumption that fires frequently swept through the marshes; they believe the wet marsh would not support fires. Perhaps fire was restricted to drought years or occurrences of winter lightening storms.

The possibility of burning having a detrimental effect on the orchid does exist if the fire occurs during a crucial growth phase or if the fleshy surface tubers are damaged by fire (P. Sundt, pers. comm. 23 Jan. 1990; The Nature Conservancy Arizona Field Office, pers. comm.) Controlled burning maintains the appropriate habitat for some orchid species (Dressler 1981). Some species in South Africa and Australia flower only after fires, some flower more prolifically without fire, and the flowering of some other species is unaffected by fire (Dressler 1981). Several prairie orchids, such as Spiranthes cernua, sand-prairie ecotype, and Spiranthes lacera, appear to increase the number of flowering plants after burns (conditions of the burns were not indicated); possibly, fire physiologically triggers the bloom stage (Sheviak 1974; Sanford 1974; B. Jennings, pers. comm. 25 Jan. 1990). Orchids with protected underground buds tend to benefit (increase in number of flowering plants) or be unaffected by fires, whereas species with surface pseudobulbs require protective rocky spots in order to survive fires (Sanford 1974).

Most likely, the timing of a fire is extremely critical. A burn at one site conducted in April 1979 resulted in the increase in orchid number from 40 to 196 in August following the fire (McClaran and Sundt 1992; The Nature Conservancy Arizona Field Office, pers. comm.). However, the number of plants growing in unburned locations also increased during this period, so possibly other environmental conditions were responsible for the significant increase in number of orchid plants (McClaran and Sundt 1992; The Nature Conservancy Arizona Field Office, pers. comm.). A fire conducted in May 1986 resulted in a decrease in population size from 97 (flags, presumably indicating orchids from the previous year) to 8 plants (McClaran and Sundt 1992; The Nature Conservancy Arizona Field Office, pers. comm.). The difference in the effect of the second fire compared to the 1979 fire may be due to the more advanced, vulnerable growth stage of the orchid in May. These results indicate the importance of determining the most beneficial time of burning. The effects of high fuel loads and temperature of burns in the cienega should be determined in order to prevent damage to the tuber by hot fires.

Gehlbach (1986) emphasizes the importance of grazing on marsh vegetation. Over the past 10,000 years periodic exposure of southern Arizona cienegas to mammoths, Spanish cattle and Anglo livestock have resulted in trampling and grazing. Gehlbach (pers. comm. 25 Feb. 1990) feels that short durations of heavy grazing, analogous to the conditions of migratory animals, may be a natural and efficient means of managing the cienega. Livestock possibly aids in the survival of the orchid by tilling the soil, providing appropriate microsites for seedling establishment, and decreasing the litter accumulation. McClaran and Sundt (1992) suggest that grazing at one site and the exclusion of grazing at another site may explain the more abundant orchid plants at the former location. Spiranthes at the first site grow in a more open and less crowded vegetative (not necessarily more natural) setting than those at the second site (P. Sundt, pers. comm. 23 Jan. 1990). Possibly, cattle grazing may aid in the orchid growth by reducing the competition of neighboring grasses for space and nutrients (Fernald 1987). However, the populations at both of these sites are both described as decreasing in the number of flowering plants over the past ten years (M. McClaran, pers. comm. 24 Jan. 1990), thus damaging the argument of the effectiveness of grazing. Due to the absence of grazers for thousands of years, between the period of mammoths and cattle, Heitlinger (pers. comm. 8 Jan. 1990) feels that a non-grazing disturbance was most likely associated with the recent evolution of this orchid.

Management experiments on Spiranthes spiralis indicate that grazing by rabbits cleared the vegetation and provided sites for seed germination eleven years prior to the study. This is evident by the increase in number of autotrophic seedlings of a species that requires eleven years of saprophytic development prior to emergence (Wells 1981). This experiment suggests the long-term time span required to assess the response of a Spiranthes species to a particular management technique.

The rare orchid Spiranthes magnicamporum increases significantly in lightly grazed areas, but apparently the benefit from grazing is not due to increases in light level; the optimum grazing level is so low that there is no significant reduction in vegetation (Sheviak 1974).

Casual observations indicate a high concentration of several Spiranthes species in grazed areas. The rare S. parksii, which grows in open, grassy woodland sites in Texas, is most abundant in areas exposed to heavy cattle grazing; the S. romanzoffiana growing in Alaska is especially abundant along moose trails: Gehlbach (pers. comm. 25 Feb. 1990) suggests the possiblity of the hoof-turned soil benefitting the establishment and/or survival of the plants. Higher concentrations of S. cernua and S. gracilis are found growing beside horse trails than in areas distant from horse trails; the plants occur close to the trail where the effects of the hooves are present, but far enough from the trail to be out of reach of the grazers (F. Gehlbach, pers. comm. 25 Feb. 1990). Detrimental effects of grazing are illustrated by the apparent (but not confirmed) extirpation of a population of Spiranthes diluvialis plants in Utah in a heavily grazed field (Sheviak 1984).

The species may have a number of additional management needs although the research needed to identify these needs has not be completed. These needs include: (1) maintenance of the hydrologic regime; (2) control of exotics like Johnson grass; and (3) reduction of accumulated litter to increase light and water availability to orchids.

Maintenance of the hydrologic regime may require the retirement or reduction of grazing in the watershed to (i) stabilize spring flows and (ii) reduce the probability of a scouring flood and channel erosion, thus ensuring that water table depths remain near the surface.

Flooding of marshy species has most likely resulted in the apparent decline or extirpation of Spiranthes populations in southern Arizona and Utah (Sheviak 1984, McClaran and Sundt 1992). However, Gehlbach (pers. comm. 25 Feb. 1990) speculates on a beneficial scheme of periodic flash floods playing a historical role in restoring favorable conditions for the orchid by removing the dense vegetation cover.

Control of exotic species like Johnson grass can be accomplished by (i) frequent mowing in areas that are completely dominated by Johnson grass and too dry to support Spiranthes and (ii) hand-application of herbicides to weeds in areas that are dominated by native species.

Many orchid species cannot compete with fast growing, large herbaceous plants. The population size of Spiranthes spiralis growing in areas where land is frequently disturbed (mowed, plowed, etc.) decreases when tall grasses or dense short grasses increase in abundance (Sanford 1974). Spiranthes ovalis is a rare plant under undisturbed conditions; however, it readily invades areas that have been altered, particularly abandoned wooded pastures and old fields (Sheviak 1974). Cypripedium candidum and Spiranthes lacera thrive in sites where annual mowing occurs (Curtis 1946; Sheviak 1974). A recovery in the number of Cypripedium candidum plants was seen within five years of initiation of mowing practices which reduced the amount of shrubs (Curtis 1946). In mowed sites, flowering of Spiranthes lacera is directly dependent (the dependency was not explained) on the clipping regime (Sheviak 1974).

Reduction of accummulated litter can be accomplished by prescribed burning, grazing, mowing, or clipping. Disagreement over the most natural management regime for the Spiranthes exists, with several individuals suggesting burning (M. Heitlinger, pers. comm. 8 Jan. 1990; P. Warren, pers. comm. 25 Jan. 1990) and others recommending grazing (Gehlbach 1986; P. Sundt, pers. comm. 23 Jan. 1990). Manipulations which alter the soil characteristics should be avoided in the fall when the seeds are most likely beginning to germinate and commence the mycorrhizal relationship; in many orchid species the initial orchid-fungi association is extremely precarious (Wells 1981).

More information on the orchid's life-cycle and environmental requirements and experimentation on the effect of different management practices (grazing, fire, mowing, clipping) are needed to identify the most effective management procedures.

Monitoring Requirements: Monitoring Spiranthes delitescens at all known sites is needed to assess the current status of the species. There is some background information on population numbers of aboveground plants at two well-studied sites. Both populations appear to be declining; the declines have been most dramatic at one site. There are no estimates of population size for the other two populations which are known only from collection records. Monitoring can also be used to understand the developmental processes and ecological requirements of this species, thereby increasing our ability to accurately forecast and interpret population fluctuations.

A permanent marking system should be employed, allowing for continual monitoring of individual plants. The position of each plant should be labelled with respect to the perimeter of the specific plot in which the plant is contained. Labelled stakes, indicating the precise location, should be placed consistently on one side (i.e. due north) of each plant. McClaran and Sundt (1992) use a 1 m X 1 m square placed over permanent corner stakes to mark the plot boundary, and each plant is labelled with both the distance to each stake and the direction (E or W) relative to the line connecting the two stakes.

Yearly vegetative and floral measurements should be taken consistently in August, during the period of flower and fruit development. Measurements on each individual plant should include presence or absence of vegetative and floral growth, height of shoot and inflorescence and number of flowers and fruits. The percentage of mature fruits which contain seeds is valuable information, since some Spiranthes species develop fruit without producing seeds (Catling 1982). Along with the yearly detailed monitoring, visual observations of the vegetative conditions (presence or absence of leaf rosettes) throughout the year should be noted.

The environmental requirements for germination, growth, survivorship and reproduction are unknown for Spiranthes delitescens. If research indicates that one or more of the following environmental parameters are important, then this parameter(s) should also be monitored on a monthly or biweekly basis throughout the growing season. Potentially important environmental parameters may include: soil temperature, moisture, pH, light intensity at soil level and 10 cm above the soil level (orchid leaf level), and precipitation. Possibly, complete soil analyses should be performed periodically in order to determine differences in mineral availability and microorganism diversity at the various sites.


Management Programs: Burning experiments are being planned for one protected site. The study site will be divided into thirds and the three treatments will include a control, burns conducted every two years and every seven years. Contact: Mark Heitlinger, Director of Stewardship, The Nature Conservancy, Arizona Field Office, Tucson, Arizona.
Monitoring Programs: Several monitoring programs are currently underway at one protected site.

Contacts: Peter Warren/Dave Gori, The Nature Conservancy, Arizona Field Office, Tucson, Arizona 85705; (602) 622-3861. The monitoring plan for Spiranthes includes counts of vegetative and reproductive individuals in eleven experimental plots that were randomly assigned one of three prescribed burn treatments. Dave Gori has received funds from The Nature Conservancy to develop a monitoring plan for S. delitescens in 1992.

Mitchel McClaran and Peter Sundt, Department of Range Management, University of Arizona, Tucson, Arizona 85721; (602) 621-1673. Vegetative and floral parameters of the Spiranthes have been monitored by various people from 1978 to 1989 (McClaran and Sundt 1992).

Judy Davis, Department of Hydrology, University of Arizona, Tucson, Arizona 85721; (602) 621-1723. Monitoring of several hydrological features at the cienega have been conducted from 1988 to 1990 (J. Davis, pers. comm. 29 Jan. 1990).

Spiranthes spiralis was monitored from 1963 until 1980 at the following location: Knocking Hoe National Nature Reserve, Bedfordshire, England (Wells 1981).

Management Research Programs: The Nature Conservancy is now conducting a long-term study to assess the effect of prescribed burns and burn frequency on the structure and composition of cienega vegetation and Spiranthes. For more information about this study, contact: Dave Gori, The Nature Conservancy, 300 E. University Blvd., #230, Tucson, Arizona 85705; (602) 622-3861.

Cytological and morphological studies have been performed by: Charles Sheviak, Botanist, New York State Museum, Albany, New York.

Management Research Needs: Extensive research is required to understand the life-cycle, ecology, environmental requirements, and response to manipulations of Spiranthes delitescens. The lack of information is due to the recent identification of the southern Arizona plants as a new species and the complex life-cycle of the group which include saprophytic individuals that can live underground for an unknown period of time.

The most important research need is to develop and collect data to validate an ecological model of this species in its natural habitat.

The complete characterization of this species' life-cycle and environmental requirements is needed. Most likely this species is a perennial; if so, what type of underground structures exist? Does vegetative reproduction play a major role in the propagation? What, if any, specific soil fungi are required for germination and maturation? How long does this species remain underground saprophytically and can it revert back to a saprophytic stage when environmental conditions are unfavorable? How many years before a plant reaches reproductive maturity? What is the optimum light level and minimum temperature for efficient photosynthesis? Are specific environmental cues required to trigger flowering? Is cross-pollination more prevalent than self-pollination?

Important in studying the effect of manipulations is determining what parameter of plant development should be used to measure optimum growth: percentage of plants flowering, height of inflorescence, number of vegetative plants, number of seedlings, or some other unidentified important characteristic. Laboratory, greenhouse and field experiments are needed to answer these and many other critical questions before we can understand the impacts of various manipulation techniques.

Experiments to determine the response of plants to different management regimes should be conducted; however we cannot elucidate or predict how the plant will physiologically be affected by a treatment until the biology of this species is unravelled. Along plant monitoring in different locations, experimental plots should be employed to test the effects of burning, mowing, and grazing on the plants.

Experimental burns, varying in frequency and the month conducted, are important in determining the response of this species to fires. Spring burns, prior to plant development, may provide necessary and natural litter removal without damaging the orchid.

Grazing experiments should be conducted to study the impact of various densities and species (rabbits, cattle, horses) of grazers, as well as season and duration of grazing. Gehlbach (pers. comm. 25 Feb. 1990) suggests setting up a plot which excludes cattle at an otherwise grazed site, and one which includes cattle at an otherwise ungrazed site, in order to look at the effects of grazing in a nongrazed site versus the absence of grazing in a previously grazed site.

The bending of plants, without removal, away from the orchids would provide information on the relationship between light level and nutrient availability (McClaran and Sundt 1992). The use of a photometer in these studies may allow correlations between light level and orchid growth to be drawn.

Genetic studies to determine the genetic structure of the four known S. delitescens populations and to assess the amount of variation within and between populations may be important in developing a recovery program for the species which may include propagation of plants for reintroduction and collection of seed for storage.

Population/Occurrence Delineation Not yet assessed
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Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 20Sep1996
NatureServe Conservation Status Factors Author: Maybury, K. (rev by S. Swartz); D. Newman (1992), rev. A. Olivero (2003), rev. S. Schuetze (2011)
Management Information Edition Date: 01Mar1992
Management Information Edition Author: DARA NEWMAN
Element Ecology & Life History Edition Date: 01Mar1992
Element Ecology & Life History Author(s): D. NEWMAN, rev. S. Schuetze (2011-08-03)

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
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  • Arditti, J. 1982. Orchid biology, reviews, and perspectives. Cornell University Press, Ithaca, NY. 390p.

  • Arizona Game and Fish Department. 2000. Spiranthes delitescens. Unpublished abstract compiled and edited by the Heritage Data Management System, Arizona Game and Fish Department, Phoenix, AZ. 4 pp.

  • Bender, J. 1986. Element stewardship abstract for Cypripedium candidum. The Nature Conservancy. Midwest Regional Office, Minneapolis, MN.

  • Catling, P. 1982. Breeding systems of northeastern North American SPIRANTHES. Canadian Journal of Botany 60: 3017-3034.

  • Catling, P. and V. Catling. 1988. SPIRANTHES NEBULORUM a new species from southern Mexico and Guatemala. Rhodora 90:139-146.

  • Curtis, J. 1946. Use of mowing in management of white ladyslipper. Journal of Wildlife MAnagement 10(4): 303-308.

  • Dressler, R. 1981. The Orchids: Natural History and Classification. Harvard Univ. Press, Cambridge, MA. 332 pp.

  • Fernald, A. 1987. Plant community ecology of two desert marshes in southeastern Arizona. M.A. thesis, University of Colorado, Boulder.

  • Flora of North America Editorial Committee. 2002a. Flora of North America North of Mexico. Vol. 26. Magnoliophyta: Liliidae: Liliales and Orchidales. Oxford Univ. Press, New York. xxvi + 723 pp.

  • Gehlbach, F. 1986. Professor, Department of Biology, Baylor University. Correspondence, TNC files, Tucson, Arizona.

  • Grater, R. 1973. Canelo Hills Cienega, an evaluation. The Nature Conservancy files, Tucson, AZ.

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Luer, C.A. 1975. The native orchids of the United States and Canada excluding Florida. New York Botanical Garden. 361 pp.

  • McClaran M.P., and P.C. Sundt. 1992. Population Dynamics of the Rare Orchid, Spiranthes delitescens.The Southwestern Naturalist 37(3): 299-303.

  • Merrigan, S. 1990. Element stewardship abstract - Cienega (in preparation). The Nature Conservancy, Tucson, AZ.

  • Rutman, S. 1992. Handbook of Arizona's endangered, threatened, and candidate plants. U.S. Fish and Wildlife Service, Phoenix, Arizona.

  • Rutman, S., and J. Rorabaugh. 1995. Endangered and threatened wildlife and plants: Proposal to determine endangered status for three wetland species found in southern Arizona and northern Sonora. Federal Register 60(63): 16836-16846.

  • Sanford, W. 1974. The ecology of orchids. In C. Withner, editor, The orchids, scientific studies. John Wiley & Sons, New York, NY. 1-101p.

  • Sheviak, C. 1974. An introduction to the ecology of the Illinois Orchidaceae. Illinios State Museum, Springfield, IL. 89p.

  • Sheviak, C.J. 1984. Spiranthes diluvialis (Orchidaceae); a new species from the western U.S. Brittonia 36(1): 8-14.

  • Sheviak, C.J. 1990. A new Spiranthes (Orchidaceae) from the cienegas of southernmost Arizona. Rhodora 92(872):213-231.

  • Stoutamire, W. 1974. Terrestrial orchid seedlings. In C. Withner, editor, The Orchids, scientific studies. John Wiley and Sons, New York, NY. 101-128 p.

  • Warcup, J. 1975. Factors affecting symbiotic germination of archid seed. In F. Sanders, B. Mosse, and P. Tinker. editors, Endomycorrhizeas. Academic Press, London, England. 87-105p.

  • Wells, T. 1967. Changes in a population of SPIRANTHES SPIRALIS Chevall. at Knocking Hoe National Nature Reseve, Bedfordshire, 1962-65. Journal of Ecology 55:83-89.

  • Wells, T. 1981. Population ecology of terrestrial orchids. In H. Synge, editor, The biological aspects of rare plant conservation. John Wiley and Sons, New York, NY. 181-195 p.

  • Williams, L. 1951. The Orchidaceae of Mexico. Cieba 2:1-132.

  • van der Pijl, L., and C. Dodson. 1966. Orchid flowers: Their pollination and evolution. Unversity of Miami Press, Coral Gables, Florida. 214 pp.

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