Asclepias tonkawae
| Asclepias tonkawae | |
|---|---|
 | |
| Asclepias tonkawae in flower, note the recurved lobes | |
Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Embryophytes |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Gentianales |
| Family: | Apocynaceae |
| Genus: | Asclepias |
| Species: | A. tonkawae |
| Binomial name | |
| Asclepias tonkawae D.P.Duran, J.Ksepka, S.A.Davis, Godwin & R.A.S.Laroche | |
Asclepias tonkawae, the skirt milkweed, is a species of flowering plant in the family Apocynaceae. It is endemic to the U.S. state of Texas, where it occurs in sandy upland habitats.[1][2]
Taxonomy
The species was formally described in 2025 by Daniel P. Duran and collaborators following a phylogenomic study of Asclepias tomentosa.[2] The species was previously included within Asclepias tomentosa, but genetic and morphological evidence supported its recognition as a distinct species.[2]
Phylogenomic analyses revealed that Texas populations formed a deeply divergent lineage, reciprocally monophyletic with respect to eastern populations of A. tomentosa.[2] Population genetic analyses showed high levels of differentiation (FST ≈ 0.296–0.357), supporting species-level separation.[2]
Description
Asclepias tonkawae is a perennial herb growing up to about 55 cm (22 in) tall from a tuberous rootstock.[2] Stems are pubescent and may be unbranched or branch after damage. Leaves are variable in shape, ranging from narrowly lanceolate to ovate, with pubescence on both surfaces and pinnate-reticulate venation.[2]
The inflorescences consist of terminal or upper axillary umbels bearing 12–25 flowers. The flowers have a green to pinkish or purplish corolla with strongly reflexed lobes that are appressed to the pedicel, a key feature distinguishing the species from related taxa.[2] Fruits are elongated follicles up to 15 cm (5.9 in) long.[2]
Distribution and habitat
The species is restricted to eastern Texas, where it has been recorded from several counties including Anderson, Franklin, Henderson, Houston, and others.[2] It occurs in xeric upland habitats associated with sandy soils, particularly the Carrizo and Sparta formations.[2]
Asclepias tonkawae is typically found in post oak savannas and sandhill habitats, often along sand ridges and ancient marine terraces.[2] It can persist in disturbed areas and is capable of vegetative regeneration from root fragments.[2]
Etymology
The specific epithet tonkawae honors the Tonkawa people, whose historic and present-day lands overlap with the species' distribution.[2] The species has been given the common name "skirt milkweed" in reference to its distinctive corolla morphology.[2]
Conservation
Because of its limited geographic range and habitat specificity, Asclepias tonkawae has been assessed as critically imperiled (G1/S1) using NatureServe criteria.[2]
Threats to the species include habitat conversion to pasture, urban development, forestry practices such as pine monoculture, herbicide use, and suppression of natural fire regimes.[2] Some populations occur within protected areas, where appropriate management may support their persistence.[2]
References
- ↑ "Asclepias tonkawae". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 23 March 2026.
- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Duran, Daniel P.; Ksepka, Jason E.; Davis, Scott A.; Godwin, William; Laroche, Robert A. S. (2025). "Phylogenomics reveals deep divergences and cryptic species within a rare sand-dwelling milkweed, Asclepias tomentosa". Ecology and Evolution. 15 (8) e71942. doi:10.1002/ece3.71942. PMC 12333076. PMID 40785997.