Astragalus hypoxylus - S. Wats.
Huachuca Milkvetch
Taxonomic Status: Accepted
Related ITIS Name(s): Astragalus hypoxylus S. Wats. (TSN 25542)
Unique Identifier: ELEMENT_GLOBAL.2.130953
Element Code: PDFAB0F470
Informal Taxonomy: Plants, Vascular - Flowering Plants - Pea Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Fabales Fabaceae Astragalus
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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: Astragalus hypoxylus
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 28Oct2013
Global Status Last Changed: 20Sep1988
Ranking Methodology Used: Ranked by calculator
Rounded Global Status: G1 - Critically Imperiled
Reasons: This species' known range is restricted to the Patagonia and Huachuca Mountains in extreme southeastern Arizona, and three locations in Yecora, Sonora Mexico. Five populations are known, one of which is in an area that is known to receive heavy recreational use.
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

NatureServe Global Conservation Status Factors

Range Extent Comments: Ranges over 2.81 sq km in Arizona. Also known from Yecora, Sonora, Mexico.

Astragalus hypoxylus was described from a collection made in the Huachuca Mountains in 1882. The description of the type locality, "Mahoney's Ranch, near Ft. Huachuca", was sufficiently vague that the site has never been relocated. The species was not seen again in the field until a collection in 1986 in the Patagonia Mountains. This population was located 3 miles south of Harshaw along the dirt road to Washington Camp. Searches elsewhere in the Patagonia Mountains have not extended the known range there by more than one mile.

Since that time other populations of A. hypoxylus have been located in the Huachuca Mountains. One population was found on the south-west side of the Huachuca Mountains near lower Bear Canyon in July, 1988. The Bear Creek population includes three sub- populations located at the Wakefield Camp turnoff just west of Bear Creek, south of the road 1/4 mile southeast of Bear Creek in a tributary (D. Gori et al. 1990), and about 3/4 of a mile west of Bear Creek (K. Johnson pers. obs.). Another population was located in Scotia Canyon in 1990.

Surveys were conducted in Sonora in 1988, 1989 and 1990, but no populations were found in Mexico. Further surveys in the Huachucas have located a population in Scotia Canyon approximately 5 1/2 miles northwest of Bear Creek. As many as 600 to 700 individuals were found there in the spring of 1991. The majority of the Scotia Canyon population is located on private land on the Peterson Ranch.

The plant was collected March 29 and March 31, 1997 (ARIZ 390294 and 390293) by T.R. Van Devender and A.L. Regina, in Yecora, Sonora, Mexico on north slope of Mesa Del Campanero and south of Maycoba on road to Moris (Chihuahua). In addition, T. R. Van Devender #2004-588, and A. L. Regina recently collected this plant from a cemetary in Yecora, Sonora, Mexico on 26 May 2004, determined by R.W. Spellenberg in 2005 (ARIZ 379027, NYBG 1267966). The species was reported to be abundant, mat-forming and in flower.

Area of Occupancy: 1-5 4-km2 grid cells
Area of Occupancy Comments: Occupies an area of approximately 2.43 sq km in Arizona.

Number of Occurrences: 1 - 20
Number of Occurrences Comments: Known from 3-4 occurrences in southeastern Arizona, and 3 locations in Yecora, Sonora, Mexico.

Population Size Comments: A conservative estimate for populations in Arizona would be <1000 individuals, but with possibly additional populations on Ft. Huachuca, the population numbers may be higher. The species was reported on 26 May 2004 by T. R. Van Devender and A. L. Regina, to be abundant, mat-forming and in flower, at a cemetary in Yecora, Sonora, Mexico.

Number of Occurrences with Good Viability/Integrity: Very few (1-3)
Viability/Integrity Comments: Peterson Ranch, Scotia Canyon in the Huachuca Mountains, Arizona, and in a cemetary in Yecora, Sonora, Mexico.

Overall Threat Impact: High
Overall Threat Impact Comments: One main threat appears to be recreation. Bear Creek receives heavy recreational use and one sub-population there has been heavily impacted due to the creation of an informal parking lot. Increased use of the site may affect nearby sub- populations. Camping and recreation use in the Patagonia Mountains does not occur near the Harshaw Road population and is no threat there (T. Deecken pers. comm.).

Second main threat to the species is climate change and drought. Populations show huge fluctuations in relation to the amount of rainfall.

The effect of fire on Astragalus hypoxylus is unknown. There has been no history of large fires in either location. Fires have been actively suppressed in both areas for the last 50-60 years and cattle grazing which reduces fine fuels may also be responsible for reducing natural fire frequencies. There has been discussion over the years about conducting prescribed burning, but so far it has not been carried out in either location. Some slash burning in connection with fuelwood collection occurred below the road near the Bear Creek area, but it is no longer done there (T. Deecken pers. comm.). Fire does not appear to be a direct threat unless the timing was such to destroy seeds and seedlings, otherwise the tough woody root stock would probably survive fire damage (P. Warren pers. comm.).

Fuelwood harvesting was done in the past in both locations and may have had some impact on populations due to trampling. The collection of dead wood was allowed in the Patagonias with a permit, but that practice was stopped in 1990. Fuelwood was harvested in the Huachucas in Sunnyside Canyon during 1986 and in Scotia Canyon during 1988. Juniper and oak were cut for fence posts in upper Bear Canyon at Wakefield Camp in 1982. These activities are no longer allowed and pose no current threat (T. Deecken pers. comm.).

Grazing has occurred in both locations since before the Coronado National Forest was established. Cattle seem to avoid eating Astragalus, causing no direct threat to A. Hypoxylus. However, trampling of seedlings, soil compaction and erosion may be indirect threats (P. Warren pers. comm.). In the spring of 1991 cattle tracks were found going through one of the Bear Creek populations and seedling numbers were significantly lower in heavily trampled areas compared to untrampled ones (J. Malusa pers. comm.). A drift fence to re-route the cattle around this population has been proposed.

Almost 1,000 head of cattle were permitted annually on the Lone Mountain Allotment which extends from the Coronado National Memorial to Parker Canyon Lake. During 1989-1991, this allotment had been stocked at around 500 head, well below the permitted number. This region includes the Bear Creek and Scotia Canyon sites. Certain areas within this allotment have problems with overgrazing such as the Bear Creek population which shows evidence of heavy trampling in some years and at Wakefield Camp which is located approximately 1.5 miles north of the Bear Creek population (T. Deecken pers. comm.).

In the 1990s only 12 head of cattle were allowed to graze in the area of the Patagonia populations (Bender Allotment). Most of the cattle have been removed from that area because of past overgrazing (T. Deecken pers. comm.). The protection needs of Astragalus hypoxylus are being considered in the present revision of both the Bender and Lone Mountain Allotments (T. Deecken pers. comm.).

Another possible indirect threat is the use of pesticides to control insect herbivores. Pesticides used to control insects such as grasshoppers may be harmful to bees and other pollinators. Bee populations may take many years to recover after spraying due to their low fecundity (J. Karron 1991). Grasshopper spraying has not yet occurred in either location on the forest (T. Deecken pers. comm.), but it has been proposed in nearby areas in Southern Arizona.

Certain bee taxa, such as Bombus, are also at risk in areas of grazing. These bees nest in abandoned rodent burrows and cattle grazing may decrease the numbers of nests by causing these burrows to collapse (Karron 1991). Since bees are the main pollinators of Astragalus species, any threat to their populations in these locations should be considered.

In summary the biggest threats to A. hypoxylus includes recreation at the lower Bear Creek population. An informal dirt parking lot has already seriously damaged one population. Increased use of the area may destroy other plants in the future. Secondly, climate change and drought is a threat to populations throughout their entire range. Populations show huge fluctuations in relation to the amount of rainfall, with mortality rates as high as 50% during years of drought. The third potential threat is degradation of habitat due to cattle grazing. Grazing has the highest impact at the Bear Creek site. There is some evidence that seedling survivorship is lower in heavily trampled areas (J. Malusa pers. comm.). Certain natural threats could also have an impact on populations, including predation of seeds by a small Chalcid wasp. Wasp predation was found to occur on 25% of the fruits in 1988. Natural threats could affect the rate of survival especially at the Bear Creek site already impacted by foot traffic and grazing.

The Mexican populations in Sonora, occur on the north slope of Mesa Del Campanero where they are locally common, along a road to Moris (Chihuahua), and in a cemetary in Yecora. Unknown what the current threats and trends are for these sights, but may include trampling by human activity, and degradation for the roadside population.

Short-term Trend: Unknown
Short-term Trend Comments: Although found in a small range in Arizona and Mexico. High mortality has been reported in past years due to drought. Populations show huge fluctuations in relation to the amount of rainfall. Current population status is not well known.

Long-term Trend: Unknown

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Environmental Specificity Comments: Open, rocky clearings in oak-juniper-pinyon woodland, on slopes of 25-30% with southerly to southwesterly exposures, generally unshaded. Substrate where found to consist of loosly consolidated, very gravelly, or cobbly soil of limestone/metamorphic mix (association with limestone uncertain for this species).

Other NatureServe Conservation Status Information

Distribution
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Global Range: Ranges over 2.81 sq km in Arizona. Also known from Yecora, Sonora, Mexico.

Astragalus hypoxylus was described from a collection made in the Huachuca Mountains in 1882. The description of the type locality, "Mahoney's Ranch, near Ft. Huachuca", was sufficiently vague that the site has never been relocated. The species was not seen again in the field until a collection in 1986 in the Patagonia Mountains. This population was located 3 miles south of Harshaw along the dirt road to Washington Camp. Searches elsewhere in the Patagonia Mountains have not extended the known range there by more than one mile.

Since that time other populations of A. hypoxylus have been located in the Huachuca Mountains. One population was found on the south-west side of the Huachuca Mountains near lower Bear Canyon in July, 1988. The Bear Creek population includes three sub- populations located at the Wakefield Camp turnoff just west of Bear Creek, south of the road 1/4 mile southeast of Bear Creek in a tributary (D. Gori et al. 1990), and about 3/4 of a mile west of Bear Creek (K. Johnson pers. obs.). Another population was located in Scotia Canyon in 1990.

Surveys were conducted in Sonora in 1988, 1989 and 1990, but no populations were found in Mexico. Further surveys in the Huachucas have located a population in Scotia Canyon approximately 5 1/2 miles northwest of Bear Creek. As many as 600 to 700 individuals were found there in the spring of 1991. The majority of the Scotia Canyon population is located on private land on the Peterson Ranch.

The plant was collected March 29 and March 31, 1997 (ARIZ 390294 and 390293) by T.R. Van Devender and A.L. Regina, in Yecora, Sonora, Mexico on north slope of Mesa Del Campanero and south of Maycoba on road to Moris (Chihuahua). In addition, T. R. Van Devender #2004-588, and A. L. Regina recently collected this plant from a cemetary in Yecora, Sonora, Mexico on 26 May 2004, determined by R.W. Spellenberg in 2005 (ARIZ 379027, NYBG 1267966). The species was reported to be abundant, mat-forming and in flower.

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 Cochise (04003), 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: An herbaceous perennial that forms a compact rosette of prostrate branches, generally less than 1 dm in diameter. Globular clusters of tiny white flowers (April-May) are borne above the flat rosette on slender stems.
Technical Description: The size of the rosette is generally less than 10 cm in diameter and the branches generally rise no more than 3 to 4 cm above the ground. The tap root is very tough and fibrous.

The alternate leaves are compound with 9 to 13 ovate leaflets that are each 3 to 5 mm long. The gray-green leaflets are glabrous above and sparsely pubescent beneath, as is the rest of the herbage of the plant. The leaflets usually appear distinctly folded along the midrib.

The inflorescence is very compact and globose, approximately 1 cm in diameter and somewhat resembling a clover inflorescence. The flowers are about 6 mm long with petals that are whitish with pale purplish tips. The inflorescences are born at the end of slender stems erect above the flat mat of foliage or horizontally beyond the edge of the mat.

The fruits are small oval pods about 8 to 10 mm long and 3 to 4 mm in diameter with a well defined groove along the ventral surface and a mucronate tip. The pods do not dehisce, but drop from the plant intact. The mature fruit are typically pale yellowish toward the base and purplish toward the tip.

Diagnostic Characteristics: The dense, subcapitate inflorescence combined with the mat-forming growth serve to distinguish this species from others that grow in the area. This is a very distinctive ASTRAGALUS that was first classified in the genus HAMOSA as HAMOSA HYPOXYLA, then subsequently synonymized with ASTRAGALUS (Barneby 1964). There has never been any disagreement as to the unique taxonomic identity of this species.
Duration: PERENNIAL, Long-lived
Reproduction Comments: Flowering occurs from April-May when temperatures range from 40 F at night to 70 F during the day. ASTRAGALUS species are usually pollinated by medium to large bees in the genera ANTHOPHORA, BOMBUS and OSMIA (J. Karron 1991). It is not known what specific species pollinates A. HYPOXYLUS. No bees have yet been observed pollinating A. HYPOXYLUS in the field, but it is assumed that it is a smaller sized bee due to the small size of the flowers. Although it is not known whether A. HYPOXYLUS is self-compatible or requires out- crossing, the diminutive size of the flower suggests that it may be self-compatible (D. Gori pers. comm.).

Fruits mature approximately three weeks after the flowers form usually during early to mid-May. In 1988, the average number of pods per inflorescence was 10 with a range of 4 to 28. The average number of seeds per pod was three with a range from one to four. Predation from a small CHALCID wasp species was found to occur on 25% of the fruit. Specimens of the wasp have been given to Carl Olson, an entomologist at the University of Arizona, for identification.

Although the seeds are indehiscent, the seed pods are light and seem to be dispersed by the wind. Seedlings are found out in the open away from parent plants. Seedlings do not appear to need a nurse plant in order to survive. However, leaf litter may be important in trapping seeds and providing a mesic microhabitat for germination (D. Gori pers. comm.). Seed longevity has not yet been determined. Seeds from both 1988 and 1991 have been sent to Aaron Liston, Herbarium Curator at Oregon State University, for germination studies (A. Liston pers. comm.).

Germination studies of A. HYPOXYLUS are currently underway at the Desert Botanical Gardens as part of the Center for Plant Conservation Program there. A combination of fifteen desiccated/frozen seeds and fifteen fresh seeds were sown in specific greenhouse conditions. The germination percentage was 86.7% for both sets of seed, indicating that freezing did not affect germination success. Most germination occurred during day- time temperatures of 73-86 F. This suggests that germination in the field would take place during or after summer rains as opposed to winter rains. Also, winter germinating seeds would be expected to have a period of dormancy through the summer and fall, while these seeds readily germinated in August. The ten remaining seedlings will be maintained and monitored for overall health and growth (L. Ecker pers. comm.).

Ecology Comments: CENSUS DATA Two monitoring plots were established along Harshaw Road in the Patagonia Mountains in 1988. All individuals within plots were marked to measure growth, survivorship, and reproductive output of established plants and the recruitment of new plants. An estimated fifteen to forty percent of the population was sampled, not the entire population. One plot measured 4 by 25 meters, the other 4 by 30 meters. One plot was located on a steep slope and had to be abandoned in 1989 when it became apparent that the survey was causing too much disturbance to plants within the plot. At this time the surrounding area within a half mile radius was also surveyed for other possible sites in the Patagonias, but no new plants were found. An additional small population was found at the Morning Glory Mine approximately 1 mile south-west of the Harshaw Road population in 1991.

Another monitoring plot was established at Bear Creek in the Huachuca Mountains in 1989 and monitoring plot #3 was established there. This plot was 8 by 1.5 meters, considerably smaller than the Patagonia plot, but the density of plants was higher. The size distribution and dynamics of the two plots have been compared since 1989.

Results of the monitoring study indicate that population size and flower production greatly fluctuate from year to year in response to climatic conditions (P. Warren et al. 1991, D. Gori et al. 1991). During the years between spring 1989 and spring 1990 recruitment was low and mortality was high, resulting in 40% reduction in population numbers within the plots at both sites. Between spring 1990 and spring 1991, there was a large increase in recruitment and a mortality rate of 5% for both locations so that populations appeared to recover from the declines of the previous year (D. Gori pers. comm.). These population fluctuations presumably reflect the drier years of 1989-1990 and the wetter year of 1991.

Among plants monitored at the Harshaw site, in 1988-1989, smaller plants were more prone to mortality, but during 1989-1990 both large and small plants died with equal probability at both sites. This suggests that the cumulative effect of two consecutive years of poor winter rainfall had an impact on plants of all sizes (D. Gori et al. 1991).

Plants were observed to die back considerably during dry years. Smaller plants tended to increase in size and larger plants decreased in size in 1989 and 1990. This implies that plant size does not necessarily correspond to plant age. The increase in plant size was considerable in 1991. Plants more than doubled in many cases at both locations reflecting the good summer and winter rains of 1990-1991.

Flowering varies greatly among individuals from year to year. In all years, larger plants were more likely to flower and they produced a greater number of inflorescences and fruits than smaller plants. Plants less than 50 mm in diameter did not flower. Plants with a diameter of 50 to 90 mm showed about 50% flowering, while individuals greater than 100 mm had 100% flowering (D. Gori per. comm.).

There is some evidence that increased precipitation results in increased fruit production. The flower and fruit count increased considerably at the Bear Creek site from 1990 to 1991 presumably as a result of the increased 1991 winter rains. No fruit count was taken in 1991 at the Patagonia plot because the cooler spring temperatures of 1991 delayed flowering and fruiting. A return trip was not made to this population, but it is assumed that increased flowering and fruiting also occurred at the Harshaw plot.

The conclusion that increased rainfall leads to increased flower and fruit production is tentative because past years have shown differences in flowering and reproduction between locations. In 1989 reproduction was good at Harshaw and not at Bear Creek. While in 1990 the reverse was true when Bear Creek showed better reproduction than Harshaw. One explanation for the differences between plots may be due to a slight difference in habitat. The Bear Creek site is a little more open and may be prone to drying out more rapidly. Although there are not marked differences in long term average rainfall between the two sites, there could be enough seasonal variation to account for differing flowering and reproduction levels. Studies of rainfall accumulation and soil moisture at the two sites may explain the annual differences between sites.

Herbivory, probably by rabbits or rodents, appears to have little impact on the plants. Levels of herbivory vary greatly between the two plots from year to year, but appear to have little effect on survivorship and future reproduction of plants.

One of the most puzzling things about this ASTRAGALUS species is its limited distribution given the abundance of apparently suitable oak woodland/savannah habitat. Continuing to observe the similarities and differences between the two study sites may give us clues about the species distribution. A closer examination of the micro-sites for rainfall accumulation, soil types, pollinator activity, herbivory, seed predation, dispersal and viability may prove useful in understanding the distribution pattern for this species.

RELATED SPECIES A. HYPOXYLUS is in the subdivision LEPTOCARPA. The two most closely related species in this group are A. PARVUS and A. NOTHOXYS (R. Barneby pers. comm.). The chromosome number of A. PARVUS is n=15 and A. NOTHOXYS is n=14 (R. Spellenberg 1976). The chromosome number for A. HYPOXYLUS is currently unknown, however seeds have been sent to Aaron Liston, Herbarium Curator at Oregon State University, for determination of chromosome number (A. Liston pers. comm.).

A. PARVUS is a Mexican species known only from western San Luis Potosi, Mexico. Little is known about this very rare species. A. PARVUS is a perennial which grows in hilly, arid grasslands at an elevation of around 7,000 ft. A. HYPOXYLUS and A. PARVUS are closely related and grouped in the subsection Parvi of Leptocarpa (Barneby 1964). They both have a tough, persisting woody root, whereas A. NOTHOXYS is a short-lived perennial. Since A. PARVUS is not found in this area there is no possibility of confusing it with A. HYPOXYLUS.

A. NOTHOXYS is a very common ASTRAGALUS of Southern Arizona which is similar in appearance to A. HYPOXYLUS. It differs from A. HYPOXYLUS in that the inflorescences are more open. The seed pods are also distinctly different. They are longer, narrower, three- sided and remain green. Although the fruit and inflorescences of the two species are distinct, the herbage is quite similar and could easily be confused at a quick glance especially during non- flowering times. A. HYPOXYLUS persists through the summer, while A. NOTHOXYS dies back after flowering in the spring.

A. NOTHOXYS is well known as a highly toxic plant to range animals, hence the common name Sheep Loco. Not all ASTRAGALUS species are poisonous. There are two types of poisoning caused by certain ASTRAGALUS species (A. Liston pers. comm.). There has been much confusion over the poisonous species due to a similarity of symptoms resulting from the two types of poisoning (O. Allen& E. Allen 1981). One type of poisoning occurs from an absorption of toxic levels of selenium from the soil. These ASTRAGALUS species are known as selenium indicators. There are only about 24 selenium absorbing species and they have smaller geographic ranges than the other poisonous ASTRAGALUS species (M. Williams and R. Barneby 1977).

The other cause of poisoning is due to alkaloid substances known as nitro-toxins. As many as 363 species have been found to contain varying levels of nitro-toxins (M. Williams and R. Barneby 1977). A. NOTHOXYS was found to have fairly high levels of nitro-toxins. Symptoms of Loco poisoning caused by nitro-toxins generally do not show up until an accumulation of the toxins have occurred in livestock. The toxins disrupt the central nervous system resulting in jerky uncoordinated movement, defective vision, hallucinations, listlessness, paralysis, and a loss of weight. Death is often the result or the animal may become permanently crippled. Given a non- loco diet, some animals do recover slowly.

Livestock usually ignore A. NOTHOXYS for feed unless other forage is lacking (E. Schmutz et al. 1968). This occurs most frequently in the spring, May and June, before the warm season grasses are up. The nitro-toxin levels are highest in the spring when ASTRAGALUS are flowering and setting fruit (M. Williams and R. Barneby 1977). ASTRAGALUS is addicting to livestock causing some individuals to continue to browse on plants even when other non-astragalus forage becomes available (E. Schmutz et al. 1968).

A. HYPOXYLUS has not been tested for nitro-toxin levels. However, because many of the species in the taxonomic section of Leptocarpa do contain nitro-toxins, it is probable that A. HYPOXYLUS also does and is poisonous to livestock (M. Williams and R. Barneby 1977). Whether it is poisonous to livestock or not may not be of great concern given its limited range. What could pose a bigger threat is confusion with the common, toxic A. NOTHOXYS in any attempts of eradication (P. Warren pers. comm.). A. NOTHOXYS has been seen growing near A. HYPOXYLUS in the Huachuca locations (K. Johnson pers. obs.). "Purple carpets" of A. NOTHOXYS were seen throughout the Huachucas in the spring of 1991 (J. Bowers pers. comm.). A. NOTHOXYS has not caused a serious enough problem in the past to require any eradication programs in either location. However, the density of A. NOTHOXYS in the Huachucas could be increasing due to overgrazing of that area and the cattle's tendency to avoid ASTRAGALUS (T. Deecken pers. comm.). Both sites with A. HYPOXYLUS populations are currently grazed by cattle.

CONSERVATION STRATEGIES FOR A. CREMNOPHALYX var. CREMNOPHALYX, A RELATED ASTRAGALUS SPECIES

The recovery project for this ASTRAGALUS species is of interest because insights learned from this project may prove useful to possible future recovery programs for A. HYPOXYLUS. A. CREMNOPHYLAX var. CREMNOPHYLAX is an endangered ASTRAGALUS of Northern Arizona. It is known only from Maricopa Point on the South Rim of the Grand Canyon where its biggest threat is trampling by Canyon tourists. Demographic studies show a decline in numbers over the last four years. U.S. Fish and Wildlife, Grand Canyon National Park, and the Arboretum at Flagstaff have combined efforts to conduct basic research targeted on reintroduction of the species. A protective fence has been put around the population and surveys for new populations have been conducted. No additional populations have been located as of 1991.

Joyce Maschinski of the Arboretum at Flagstaff has been in charge of the greenhouse germination and reintroduction studies since 1989. A. CREMNOPHYLAX flowers twice a year, from May-June and September-November. Germination occurs only in the fall (J. Maschinski pers. comm.). A. CREMNOPHYLAX is found on limestone soils.

In 1989, fifty germinated seedlings were transplanted into five different mixtures of soil, all with a combination of limestone, in the greenhouse. Mortality was low in the first five weeks of the experiment. After those first weeks mortality was high and seemed to be due to desiccation, not disease. Survival was greatest among transplants in soil containing the highest amount of limestone. This suggests that limestone soils retain water better and that A. CREMNOPHYLAX seedlings are intolerant of water loss (J. Maschinski 1991). Four month old seedlings left outdoors for the winter did not withstand subfreezing temperatures.

In 1990 experimental microsites were chosen in the field at Maricopa Point where 196 seeds were dispersed and germination was monitored. Only one seedling survived through the season although the rains were good that year. It was growing in a crack in limestone. Results indicate that soil depth is crucial to the survival rate of the seedlings. Greenhouse studies found that seedlings were highly susceptible to desiccation. Soil depths less than 3 cm are probably too shallow to maintain adequate soil moisture while depths greater than 5 cm are prone to frost heaving killing the seedlings. The experimental microsites used in the study had soils deeper than 5 cm.

Field and greenhouse observation of seed dispersal and germination indicate that seed dispersal of A. CREMNOPHYLAX is poor. The seed pods open onto the parent plant so that seeds do not leave the vicinity of the parent plant. Seeds usually germinated within 10 cm of the adult plants. This pattern of seedling establishment may influence gene flow in the population. Genetic studies on inbreeding depression would be useful.

Seedlings observed in the field appear to need nurse plants to provide protection from drought, sun and wind. Seedling success appears to be higher among those that are near other nurse plant species as opposed to those growing next to the parent plants.

Seed germination occurs in the fall after the monsoon season. This timing, after the monsoons as opposed to during them, seems surprising given that the mortality of the seedlings peaked in the fall and was due to desiccation. Winter mortality ranged from 20- 33%. Seedlings appeared to have high survivorship if they were able to persist until the spring. These observations were made from the fall of 1990 to the spring of 1991. Survivorship may vary somewhat from year to year in response to climatic variation.

Results of these studies reveal a germination and survival rate much lower than expected. Although greenhouse germination indicated 49% germination, field germination in 1990 was only 10% with 0.05% survival (J. Maschinski 1991). Aside from the requirements of soil depth and the need for nurse plants, seed viability may have been a problem. The seeds used in the study were over a year old. Seed longevity of A. CREMNOPHYLAX is not known. Additional work is needed to improve germination and establishment success of this very rare plant species (J. Maschinski 1991).

These studies indicate that A. CREMNOPHYLAX has specific germination requirements with respect to soil depth, moisture and composition. Given the similarities between restricted A. CREMNOPHYLAX and A. HYPOXYLUS, this study may give us clues about germination requirements of A. HYPOXYLUS. Both species are long- lived perennials with woody rootstocks, both appear to be intolerant to drought, especially when young, and both grow on limestone soils.

STUDIES ON THE GENETICS AND BREEDING SYSTEMS OF RELATED ASTRAGALUS Awareness of genetic principles and genetic variation in populations facilitates intelligent intervention or helps to avoid disturbances and harmful interference (O. Frankel 1983). Pertinent studies have been done on the genetic structure and breeding systems of certain geographically restricted and widespread ASTRAGALUS species (J. Karron 1988, 1989). Karron (1988) tested the hypothesis that species with small ranges and few individuals exhibit low levels of genetic polymorphism whereas widespread species with large populations have higher levels of genetic variability. The four species compared were, A. LINIFOLIUS, A. OSTERHOUTI, A. PECTINATUS and A. PATTERSONI.

The first two species have restricted geographic ranges and small populations, the latter two are widespread with large populations. The first three are in the same taxonomic section, Pectinati, while the fourth species, A. PATTERSONI, is not as closely related. These four species have an overlapping distribution in northwestern Colorado. Comparing co-occurring congeners is important because they are likely to be exposed to similar selection pressures and ecological constraints (J. Karron 1991). Results of the study indicate that although A. LINIFOLIUS, a restricted species, showed somewhat lower levels of polymorphism than widespread A. PECTINATUS, it had relatively higher levels of polymorphism than the widespread A. PATTERSONI. A. OSTERHOUTI had fairly low levels of polymorphism as expected of restricted species.

One criticism of this study is that the four species examined were not all closely related (A. Liston pers. comm.). However, the study does indicate that levels of polymorphism among restricted and widespread species do vary more greatly than was first assumed. Studies done with genera of other restricted and widespread species support these findings (J. Karron 1991).

The study also revealed levels of genetic differentiation among different populations of A. OSTERHOUTI (J. Karron et al. 1988). A rare California ASTRAGALUS, A. CLARIANUS, has also been found to contain differing levels of polymorphism between populations (A. Liston pers. comm.). This suggests the importance of conserving genetic material from as many populations as possible (J. Karron 1991).

Factors other than present population size and distribution may influence levels of genetic variation. Habitat and the effects of different soil types may play a role. Historical factors including population bottlenecks within populations may also affect the level of polymorphism. Restricted taxa which are of relatively recent origin and have never occupied a large range are known as neoendemics. Other restricted taxa which were once widespread and have just recently declined in range are called paleoendemics (J. Karron 1987). Such differing historical backgrounds could account for different levels of polymorphism within restricted species.

Karron (1989) tested the prediction that species with restricted ranges and few individuals are more likely to be self-compatible and to exhibit low levels of inbreeding depression than are geographically widespread congeners. Controlled pollinations were conducted in the field on populations of four ASTRAGALUS species, two restricted and two widespread, in order to investigate the predicted patterns of self-compatibility and inbreeding depression. They were restricted A. LINIFOLIUS and A. OSTERHOUTI and widespread A. LONCHOCARPUS and A. PECTINATUS. The first three species, including widespread A. LONCHOCARPUS, were found to be self- compatible, while widespread A. PECTINATUS was essentially self- incompatible. Contrary to predicted patterns, results showed that inbreeding depression was evident in the restricted A. LINIFOLIUS, but not in progeny of the widespread A. LONCHOCARPUS. A. LINIFOLIUS has a high genetic load in contrast to many other rare taxa which have very low levels of genetic variation.

These studies indicate that it is difficult to make generalizations about the genetic structure of closely related species. Variation among species in genetics and breeding systems characteristics suggests that population management programs should be individually tailored for certain rare species. Studies on the genetics and breeding systems of rare species may be essential for determining appropriate strategies for species recovery programs, in particular understanding levels of polymorphism, outcrossing and inbreeding depression.

Terrestrial Habitat(s): Forest/Woodland, Savanna, Woodland - Hardwood
Habitat Comments: SUMMARY: Open, rocky clearings in woodland. The dominant vegetation includes Emory oak (Quercus emoryi), Mexican blue oak (Q. oblongifolia), alligator juniper (Juniperus deppeana), and Mexican pinyon (Pinus discolor). The clearings are generally sunny with a southerly exposure. The substrate is loosely consolidated, very gravelly or cobbly soil composed of a mixture of limestone and metamorphic rock. The plants grow on hillsides of varying steepness from nearly level up to 25 to 30 percent. Most sites lie at an elevation of approximately 1675 m, with maximum elevations observed near 1866 m. END SUMMARY. Little is known about this rare plant. At the 3 Arizona sites from which it is known, it is found in open, rocky clearings in woodland. The dominant vegetation includes Emory oak (Quercus emoryi), Mexican blue oak (Q. oblongifolia), alligator juniper (Juniperus deppeana), and Mexican pinyon (Pinus discolor). The clearings are generally sunny with a southerly exposure. The substrate at these 3 sites is loosely consolidated, very gravelly or cobbly soil composed of a mixture of limestone and metamorphic rock. The plants grow on hillsides of varying steepness from nearly level up to 25 to 30 percent. All 3 Arizona sites lie at an elevation of approximately 1675 m. At the 3 known Mexican sites, it is an abundant, mat-forming hercaceous perennial located in a cemetary on grassland in open pine-oak forest; along a roadside where it is locally common; and in level, rocky stream with oak woodland on hillside.

CLIMATE The closest known weather stations to the Arizona sites are at Fort Huachuca, Canelo Hills and Patagonia. They show similar average annual temperatures and rainfall (Sellers 1985). The Patagonia station does not collect temperature data. The two rainfall averages for Patagonia come from two locations over the history of the station (P. Warren et al. 1991).

STATIONS Ft. Huachuca Patagonia* Canelo Elevation 4664' 4044' 5000' Location 31'35'N 31'33'N 31'33'N 110'20'W 110'45'W 110'31'W Mean Annual Min Daily T 48.9 F --- 40 F Mean Annual Max Daily T 74.8 F --- 74 F Mean Annual Rainfall 15.39" 17.70"/ 17.82" 16.12"

Economic Attributes
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Economically Important Genus: Y
Management Summary
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Stewardship Overview: Although A. Hypoxylus shows successful reproduction, the species is potentially vulnerable due to population fluctuations and its limited distribution. It is essential to maintain monitoring of the species and conduct research and management programs including recreation and livestock management in order to protect the known populations.
Restoration Potential: At present there is not enough evidence of a decline in the populations to require a recovery program. What is important is to maintain the quality of present populations to guard against any possible future decline. At two known locations the species shows evidence of successful reproduction, multiple size/age classes, growth, flowering and fruits produced by plants and together these indicate a high recovery potential.
Preserve Selection & Design Considerations: Our current understanding of this species suggests that protection can be accomplished through acquisition and/or management of the actual occurrence, EO. We do not understand how natural processes acting outside of the area where plants occur affect the species, so that recommendations for buffer areas are premature at this point. Both the Bear Creek and Harshaw Road populations occur on Forest Service Land; the Scotia population is on private land. These populations are not currently protected in the sense that they are subject to specific management guidelines, however, the species is being considered in the Forest Service's revision of the Bender and Lone Mountain Allotments. Private property in Scotia Canyon should be put in protective management either in the form of acquisition by the U.S. Forest Service or a conservation easement agreement with the landowner.
Management Requirements: The management needs include the improvement of both recreation and livestock management. Management needs also require the continuation of intensive monitoring. Although the species is not at present risk, the large fluctuations in population size due to drought make the species potentially vulnerable.

Parking and foot traffic management is essential at the Bear Creek populations. Increasing uncontrolled parking and foot traffic on the weekends needs to be kept in check. Relocation of the parking lot has been suggested. Construction of a drift fence has also been proposed to keep cattle out of the canyon bottom at Bear Creek. A drift fence would re-route cattle around the population to keep them from trampling seedlings.


Management Programs: Species management is being considered in the current revision of the Bender and Lone Mountain grazing allotments by the U.S. Forest Service.
Monitoring Programs: One program underway since 1988. Contact: Peter Warren, Public Lands Protection Planner, The Nature Conservancy, Arizona Field Office, Tucson, Az. (602) 622-3861
Management Research Programs: Seeds have been sent to Aaron Liston, Herbarium Curator at the Oregon State University, Corvallis, Oregon, to determine seed viability and chromosome number. Contact: Aaron Liston, Herbarium Curator, Herbarium, Botany and Plant Pathology Dept., 4082 Cordley Hall, Oregon State University, Corvallis OR., 97331, (503) 737- 5301.

Germination studies are also being conducted at the Desert Botanical Gardens as part of the Center for Plant Conservation program. Contact: Liz Ecker, Curator of the Living Collection, Desert Botanical Gardens, 1201 Galvin Parkway, Phoenix, AZ 85008, (602) 941-1225.

Management Research Needs: There are many research needs for A. HYPOXYLUS in order to better understand population fluctuations and what limits the species' distribution. Soil studies including the germination of seedlings in different soils may provide answers to its limited distribution. Seedling germination and survivorship studies could help determine what limits seedling recruitment. Rainfall studies could help clarify the cause of population fluctuations and differences between the two locations. Seed predation and seed viability need to be examined. A study of the breeding systems could answer questions about self-compatibility and inbreeding depression. Finally, studies in the genetics could reveal differing levels of polymorphism between the disjunct populations that may be useful in prioritizing protection effort or in designing propagation programs for reintroduction.
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: 01Mar1992
NatureServe Conservation Status Factors Author: KRISTEN JOHNSON, AZFO, rev. Maybury (1996), rev. Sue Schuetze (2011),
Management Information Edition Date: 01Mar1992
Management Information Edition Author: KRISTEN JOHNSON, AZFO
Element Ecology & Life History Edition Date: 01Mar1992
Element Ecology & Life History Author(s): KRISTEN JOHNSON, AZFO

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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  • Allen, O.N. and E.K. Allen. 1981. The Leguminosae: A source book of characteristics, uses and nodulation. The Univ. of Wisconsin Press, Madison, WI.

  • Barneby, R.C. 1964. Atlas of North American Astragalus. 2 Vols. New York Botanical Garden, Bronx, New York. 1188 pp.

  • Frankel, O. H. 1983. Foreword. In genetics and conservation: a reference for managing wild animal and plant populations, eds. C. M. Schonewald-Cox et al. The Benjamin/Cummings Publishing Co., Inc. Menlo Park, CA.

  • Gori, D.F., J. Malusa, P.L. Warren and W.S. Monarque. 1991. Population studies of sensititve plants of the Huachuca, Patagonia and Atascosa Mountains, Arizona. Submitted to Coronado National Forest in completion of P.O. 40-8197-0-0215. The Arizona Nature Conservancy, Tucson, AZ.

  • Gori, D.F., P.L. Warren and L.S. Anderson. 1990. Population studies of sensitive plants of the Huachuca, Patagonia and Atacosa Mountains, Arizona. Submitted to Coronado National Forest in completion of P. O. 40-8197-9-0119. The Arizona Nature Conservancy, Tucson, AZ.

  • Karron, J. D. 1991. Patterns of genetic variation and breeding systems in rare plant species. In Conservation of rare plants: Biology and genetics, eds. D. Faulk and K. Holsinger. Oxford University Press, Oxford, U. K.

  • Karron, J.D. 1987a. A comparison of levels of genetic polymorphism and self-compatibility in geographically restricted and widespread plant cogeners. Evolutionary Ecology 1:47-58.

  • Karron, J.D. 1989. Breeding systems and levels of inbreeding depression in geographically restricted and widespread species of Astragalus (Fabaceae). American J. of Botany 76(3):331-340.

  • Karron, J.D., Y.B. Linhart, C.A. Chaulk and C.A. Robertson. 1988. Genetic structure of populations of geographically restricted and widespread species of Astragulus (Fabaceae). American J. of Botany 75(8):1114-1119.

  • 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.

  • Kearney, T.H., R.H. Peebled y Colaboradores. 1951. Arizona Flora. University OF California Press. Berkeley y Los Angeles, California. E.U.A. 1030 PP.

  • Levin, G.A. 1987. Noteworthy collections: Astragalus hypoxy S. Wats. (Fabaceae). Madrono 34(2):170.

  • Maschinski, J. 1990a. Propagation of Astragalus cremnophylax var. cremnophylax and reintroduction to the South Rim of Grand Canyon National Park. Submitted to: U.S. Dept. of the Interior, Fish and Wildlife. Report of ongoing research order #20181-88-01138. May 1990. The Arboretum at Flagstaff, Flagstaff, AZ.

  • Maschinski, J. 1990b. Reintroduction of Astragalus cremnophylax var. cremnophylax. Submitted to: U.S. Dept. of the Interior, Fish and Wildlife. Report of ongoing research order #20181-88-01138. November 1990. The Arboretum at Flagstaff, Flagstaff, AZ.

  • Maschinski, J. 1991. Integrated conservation strategies for recovery of Astragalus cremnophylax var. cremnophylax at the South Rim of Grand Canyon National Park. Submitted to: Proceedings of the First Biennial Conference on Research at Flagstaff, Flagstaff, AZ.

  • Schmutz, E.M., B.N. Freeman, and R.E. Reed. 1968. Livestock-poisoning plants of Arizona. Univ. of Arizona Press, Tucson, AZ.

  • Sellers, W.D., R.H. Hill, and M. Sanderson-Rae. 1985. Arizona climate: the first hundred years. University of Arizona, Tucson, Arizona.

  • Spellenberg, R. 1976. Chromosome numbers and their cytotaxonomic significance for North American Astragalus (Fabaceae). Taxon 25:463-476.

  • Turner, N.J. and A.F. Szczaawinski. 1991. Common poisonous plants and mushrooms of North America. Timber Press, Portland, OR.

  • Warren, P.L., D.F. Gori, B. Gebow and J. Malusa. 1991. Status report: Astragalus hypoxylus Watson. Submitted to U.S. Dept. of the Interior, Fish and Wildlife Service. The Arizona Nature Conservancy, Tucson, AZ.

  • Warren, P.L., L.S. Anderson and P.B. Shafroth. 1989. Population studies of sensitive plants of the Huachuca and Patagonia Mountains, Arizona. Submitted to Coronado National Forest in completion of P.O. No. 40-8197-9-431. The Arizona Nature Conservancy, Tucson, AZ.

  • Williams, M.C. and R.C. Barneby. 1977. The occurrence of nitro-toxins in North American Astragalus (Fabaceae). Brittonia 29:310-326.

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