Asclepias curtissii - Gray
Curtiss' Milkweed
Other Common Names: Curtiss' milkweed
Taxonomic Status: Accepted
Related ITIS Name(s): Asclepias curtissii Gray (TSN 30259)
Unique Identifier: ELEMENT_GLOBAL.2.145301
Element Code: PDASC020E0
Informal Taxonomy: Plants, Vascular - Flowering Plants - Dogbane Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Gentianales Apocynaceae Asclepias
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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: Asclepias curtissii
Taxonomic Comments: Distinct species.
Conservation Status
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NatureServe Status

Global Status: G3
Global Status Last Reviewed: 12May1988
Global Status Last Changed: 12May1988
Rounded Global Status: G3 - Vulnerable
Reasons: Few known occurrences and few individuals per occurrence; habitat is in decline.
Nation: United States
National Status: N3

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 Florida (S3)

Other Statuses

NatureServe Global Conservation Status Factors

Range Extent Comments: Asclepias curtissii is endemic to central and southern Florida. Although it is confirmed occurring in 23 counties, its distribution is very patchy.

Number of Occurrences: 21 - 80
Number of Occurrences Comments: 68 occurrences mapped as of October 1990.

Population Size Comments: Never abundant at a given site.

Overall Threat Impact Comments: These plants are rare and are becoming increasingly so through the destruction of scrub habitat. Residential housing and golf courses, along with clearing land for citrus trees, are responsible for the elimination of scrub habitat where Curtiss milkweed once grew. Sand mining has also destroyed a great deal of suitable habitat.

Intrinsic Vulnerability Comments: Once established, Curtiss' milkweed is long-lived and persistent even under a relatively heavy herbivore load.

Other NatureServe Conservation Status Information

Distribution
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Global Range: Asclepias curtissii is endemic to central and southern Florida. Although it is confirmed occurring in 23 counties, its distribution is very patchy.

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 FL

Range Map
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Ecology & Life History
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General Description: Asclepias curtissii is a perennial herb that annually dies back to its rootstock. It has a long, vertical root, like a slender carrot, from which annually grows a single herbaceous stem. The leaves are opposite with short petioles and broadly ovate to oblong blades. The juice of the leaves, as well as of the stem, is thick and white and somewhat irritating to sensitive skins. The inflorescences appear at the upper nodes of the stem and are many flowered umbels. The flowers are borne on short pedicels from the umbel stalk and are small. The 5 petals are reflexed and light green, while the 5 hoods protrude stiffly forward and are white with purplish center-lines. The follicles are solitary, borne erect on declining pedicels, and are narrowly fusiform, smooth, and 10 cm long. (Putz and Minno 1987)
Technical Description: Stem decumbent or ascending, 5-7 dm long, minutely pubescent, sometimes widely branched; leaf-blades broadly elliptic to oval, varying to broadest above the middle or below it, 3-5 cm long, glabrous or nearly so; umbels many-flowered, the pedicels slender, sparingly pubescent; corolla-lobes greenish-white, lanceolate, 5-6 mm long; hood lanceolate, 4-4.5 mm long, fully twice as long as the androecium; anthers about 1.5 mm long; follicles are solitary and narrowly fusiform, smooth, and 8-11 cm long. (Small 1933)
Diagnostic Characteristics: Four other Asclepias milkweed species occur in upland habitats of Florida. Asclepias tuberosa is similar to A. curtissii in overall appearance, but has red to yellow flowers and occurs in more mesic conditions. Asclepias tomentosa non-flowering individuals are very similar to A. curtissii. The flowers are also greenish-white, but are much larger (in A. tomentosa). Where the species are sympatric, A. tomentosa replaces A. curtissii in sandhill. Asclepias humistrata is a prostrate species with foliage very distinctive from the former three milkweeds. It tends to bloom earlier than the former three species, and has pinkish flowers. It is restricted to sandhill in Florida. Asclepias feayi is a small, slender milkweed with white flowers. It is sometimes found in scrubby flatwoods, but unlike the former species, normally occurs in soil that is seasonally moist (Putz and Minno 1987).

The juvenile foliage of Asclepias curtissii closely resembles the mature foliage of Crotonopsis linearis and Croton glandulosus. The foliage of mature plants resembles Stillingia sylvatica, Palafoxia feayi, and the scrub oaks, as well as Asclepias tomentosa and A. tuberosa. Its variability in leaf shape and similarity in foliage to other species makes finding individuals of A. curtissii very difficult (Putz and Minno 1987).

Duration: PERENNIAL, Long-lived, DECIDUOUS
Reproduction Comments: Milkweeds are characteristically self-sterile. The ability of this milkweed, as well as that of other related species, to survive when the individual plants are so widely separated appears to be related to the specialized flowers that permit pollination only by certain insects that search out the scattered plants. Skipper butterflies and hairstreaks were found in abundance on flowers of Asclepias curtissii in a study conducted by Putz and Minno (1987), and are suspected to be the pollen vectors. Although transfer of pollinia to a receptive stigma is probably a rare event (relative to transfer of pollen grains), the resulting fertilization produces an entire follicle of seeds. Asclepias seeds are dispersed by wind and tend to germinate only in disturbed soil patches. Most of the seemingly suitable germination microsites within scrub are not utilized. A. curtissii seeds are intolerant of litter cover and are unable to lie dormant in the soil.
Ecology Comments: The sap of Asclepias curtissii is thick, sticky, and white. It contains low levels of cardenolides, alkaloid chemicals which are toxic to vertebrates in high concentrations (Putz and Minno 1987).

In a study by Putz and Minno (1987), deer were the major herbivores at the outset of the season, with grasshoppers removing some flowers. Aphids were present throughout the season, but were mostly restricted to actively growing plant tissue. Fulgoroids, cerambycids, and the larvae of lepidoptera appeared later in the season. Much of the stem loss during the latter part of the season was due to queen butterfly herbivory, rather than deer.

Terrestrial Habitat(s): Shrubland/chaparral
Habitat Comments: This plant grows only on the leached, excessively drained, white sand that supports scrub, sand pine scrub, and scrubby flatwoods. Associates include Florida rosemary (Ceratiola ericoides), Chapman oak (Quercus chapmanii), myrtle oak (Q. myrtifolia), sand live oak (Q. geminata) and other characteristic scrub species. Rarely do plants of this species grow together, and often several acres of scrub will appear to have no more than two or three widely scattered specimens of this rare milkweed. Asclepias curtissii has a great affinity for soil disturbance. It tends to be artificially abundant along the edges of fire lanes, sand roads, and other disturbed areas.
Economic Attributes
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Economically Important Genus: Y
Management Summary
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Stewardship Overview: 1. Locate and preserve sites where Curtiss' milkweed exist.

2. Transplant plants to sites where few individuals exist or where the Curtiss' milkweed formerly was present.

3. Establish management programs, such as fire and perhaps small localized disturbance to promote its germination and spread, and to maintain natural openings in the scrub.

Restoration Potential: Curtiss' milkweed may recover if existing known populations are secured and management programs favor seed germination and seedling establishment.
Preserve Selection & Design Considerations: To maintain this species, large contiguous acreage of scrub-type habitat should be acquired in the full range of the species.
Management Requirements: Fire management programs should be implemented in scrubs containing or having the potential to contain (e.g. adjacent seed source) Asclepias curtissii. Include soil disturbance along with fire as a component of natural diversity (Minno 1986).

Maintain scrub with fire. This should be sufficient to maintain this species.

Monitoring Requirements: Monitoring is needed to answer questions in this category, but priority is low. Presence/absence status surveys may suffice at this time.

Management Programs: The scrub habitat of this species is being actively managed at Archbold Biological Station through a fire management program. At other state and Nature Conservancy sites, management programs for the habitat are being developed.
Monitoring Programs: Monitoring being conducted by Maria Minno at Archbold Biological Station under a two year grant from the Florida Game and Fresh Water Fish Commission's Nongame Wildlife Program. For more information contact Maria Minno and Archbold Biological Station, Lake Placid, Florida.
Management Research Programs: Research is being done in the areas of distribution, density, pollination and reproductive behavior, and responses to localized disturbances and fires.
Management Research Needs: Further research needs to be done on habitat and microsite preference, and seed dispersal and germination requirements. Propagation techniques need to be established for reestablishing populations (Minno 1986).
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: 25Oct1994
NatureServe Conservation Status Factors Author: KARL BERTRAM & RONALD MYERS, TALL TIMBERS RESEARCH STATION, TALLAHASSEE, FL (9/88); A. WILDMAN, TNC-HO (10/94).
Management Information Edition Date: 20Sep1988
Management Information Edition Author: KARL BERTRAM & RONALD MYERS, TALL TIMBERS RESEARCH STATION, TALLAHASSEE, FL (9/88).
Element Ecology & Life History Edition Date: 25Oct1994
Element Ecology & Life History Author(s): K. BERTRAM & R. MYERS, TALL TIMBERS RES STA, TALLAHASSEE, FL 9/88; A. WILDMAN, TNC-HO 10/94

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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  • 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.

  • Minno, M. 1986. Quarterly report. The pollination biology and ecology of Curtiss' Milkweed (Asclepias curtissii). Visiting investigator report, Archbold Biological Station. 18 p.

  • Putz, F. E., and M. Minno. 1987. The pollination biology and ecology of Curtiss' milkweed (Asclepias curtissii). The Nature Conservancy. Fire Management and Research Program. Tallahassee, Florida.

  • Small, J.K. 1933. Manual of the southeastern flora. Two volumes. Hafner Publishing Company, New York.

  • Ward, D.B., ed. 1979. Rare and endangered biota of Florida. Vol. 5: Plants. Univ. Presses of Florida, Gainesville.

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