Flora of North America species comparison

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Asclepias cordifolia

Asclepias subverticillata

heart-leaf milkweed, purple milkweed

horsetail milkweed, poison milkweed, western whorled or horsetail or poison or whorled milkweed
Habit Herbs. Herbs.
Stems

1–20, ascending to spreading, unbranched, 25–100 cm, glabrous, glaucous, rhizomes absent.

1–8, erect, sometimes branched, few to many arrested vegetative branches usually present, 20–90 cm, puberulent with curved trichomes in a line to glabrate, not glaucous, rhizomatous.
Leaves

opposite, sessile, stipular colleters absent;

blade ovate to lanceolate, 3.5–11 × 1.8–8 cm, chartaceous, base cordate, clasping, margins entire, apex acute, mucronate, venation brochidodromous to eucamptodromous, surfaces glabrous, glaucous, margins minutely ciliate, laminar colleters absent.

3–4-whorled, sometimes opposite on vegetative branches, sessile, with 1 stipular colleter on each side of leaf base on a ciliate interpetiolar ridge;

blade linear, 3–13 × 0.1–0.4 cm, chartaceous, base cuneate, margins entire, apex acute, mucronate, venation obscure, surfaces glabrous, margins ciliate or eciliate, laminar colleters absent.
Inflorescences

terminal, branched, sometimes also extra-axillary at upper nodes, pedunculate, 5–20-flowered;

peduncle 0.3–6.5 cm, apically sparsely pilose to glabrate, with few bracts.

extra-axillary, pedunculate, 9–25-flowered;

peduncle 0.7–3.5 cm, puberulent with curved trichomes on 1 side, with 1 caducous bract at the base of each pedicel.
Pedicels

16–37 mm, sparsely pilose.

5–12 mm, puberulent with curved trichomes.
Flowers

erect to pendent;

calyx lobes elliptic to lanceolate, 3–5 mm, apex acute, pilose;

corolla red-violet, lobes reflexed with spreading tips, oval, 6–7 mm, apex acute, glabrous;

gynostegial column 1–1.5 mm;

fused anthers brown, cylindric, 1.5–2 mm, wings right-triangular, open at tip, apical appendages deltoid;

corona segments white, tinged pink to red-violet at base, sessile, tubular, 2–3 mm, exceeded by style apex, base saccate, apex truncate, oblique, glabrous, internal appendage absent;

style apex shallowly depressed, pink to red-violet.

erect;

calyx lobes lanceolate, 2–2.5 mm, apex acute, puberulent with curved trichomes to glabrate;

corolla pale green to cream, sometimes pink- or tan-tinged, lobes reflexed with spreading tips, elliptic, 3.5–4.5 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;

gynostegial column 0.8–1.2 mm;

fused anthers green, columnar, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;

corona segments cream, sometimes green- or pink-tinged or striped, stipitate, cupulate, dorsally flattened, 1.5–2 mm, exceeded by style apex, margins entire, apex obtuse, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous;

style apex shallowly depressed, green to greenish cream.
Seeds

ovate, 8–9 × 5–7 mm, margin not winged, faces reticulate-rugulose;

coma 3–3.5 cm.

ovate, 5–8 × 3.5–5 mm, margin winged, faces smooth;

coma 2–2.5 cm.
Follicles

erect on upcurved pedicels, lance-ovoid, 7.5–10.5 × 1.5–1.8 cm, apex long-acuminate, smooth, glabrous, glaucous.

erect on straight pedicels, narrowly fusiform, 6–8.5 × 0.5–0.9 cm, apex acuminate to attenuate, smooth, minutely puberulent with curved trichomes to glabrate.
2n

= 22.

Asclepias cordifolia

Asclepias subverticillata
Phenology Flowering Mar–Jul(–Aug); fruiting Jun–Sep. Flowering (Apr–)May–Oct; fruiting (Jun–)Jul–Dec.
Habitat Hill­sides, canyons, ridge tops, streamsides, seeps, basalt, serpentine, gabbro, granite, shale, limestone, talus slopes, gravel, alluvium, oak woodlands, mixed ever­green, douglas-fir, pine, pine-oak, and riparian forests, chaparral, timberline meadows, grasslands. Hills, ridges, mesas, slopes, flats, depressions, ciénegas, wet meadows, pastures, canyons, streamsides, arroyos, pond and lake margins, playas, bajadas, limestone, igneous rocks, sandstone, gypsum, clay, sandy, silty, and gravel soils, prairies, desert scrub, mesquite, juniper, and desert grasslands, pine savannas, chaparral, oak, pine-oak, pinyon-juniper, and riparian woodlands, pine and mixed-conifer forests.
Elevation 50–2200(–2800) m. (200–7200(–9200) ft.) 800–2700 m. (2600–8900 ft.)
Distribution
from FNA
CA; NV; OR
[WildflowerSearch map]
[BONAP county map]
from FNA
AZ; CO; KS; MO; NM; OK; TX; UT; WY; Mexico (Chihuahua, Coahuila, Durango, Guanajuato, Nuevo León, San Luis Potosí, Sonora, Zacatecas)
[WildflowerSearch map]
[BONAP county map]
Discussion

Fresh leaves and stems of Asclepias cordifolia are often slightly or strongly colored bluish, grayish, or purplish. This is one of the few American species of Asclepias with cavitate corona segments that lack adaxial appendages. Such species were segregated along with diverse African species in Gomphocarpus R. Brown, a polyphyletic segregate (M. Fishbein et al. 2011; D. Chuba et al. 2017). Asclepias cordifolia is a distinctive species unlike any other within its range. It is phylogenetically and geographically isolated, although not highly derived morphologically. In Nevada, A. cordifolia is restricted to the Sierra Nevada, in Carson City, Douglas, and Washoe counties. Its range extends to northern California and southwestern Oregon.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Asclepias subverticillata and A. verticillata are amply distinct away from the zone of contact from Texas to Montana. The most reliable characters for distinguishing these species are the absence of a marginal corona segment tooth and presence of arrested vegetative branches in A. subverticillata. The greater frequency of multistemmed plants and completely glabrous leaves are also characteristic of A. subverticillata. However, absence of vegetative branches in A. subverticillata is common, especially in young or poorly developed plants. It can be difficult to confidently identify incomplete specimens or immature plants in the narrow zone of parapatry. Gene flow between the species has not been investigated, and the muddy species boundaries could be attributable to past or ongoing introgressive hybridization. The identity of some populations in New Mexico, the Texas Panhandle, and western Kansas have been debated, and further study is needed to determine whether they belong to one of the parental species or are advanced generation hybrids. Asclepias subverticillata barely enters Kansas (Grant, Hamilton, Morton, Seward, Stanton, and Stevens counties) and Oklahoma (Beaver and Cimarron counties). It also appears to be rare at the northeastern end of its range in Wyoming (Carbon County), where it is thought to be extirpated. There are few occurrences of A. subverticillata disjunct from the main range and within the range of A. verticillata. There is a single, adventive population along a railroad in St. Louis, Missouri, documented in 1962 and last observed in 1970 (V. Mühlenbach 1979); it is unknown whether this population persists. Asclepias subverticillata hybridizes with A. pumila. These hybrids are usually readily detected because the parental species are distinct in leaf arrangement and internode length (whorled and distant nodes in A. subverticillata versus alternate and congested in A. pumila). Such hybrids often have mixed phyllotaxy and have been documented in northern New Mexico. Reports of A. subverticillata from Idaho are based on misidentifications of A. fascicularis and are discussed under that species. Searches for A. subverticillata in southeastern Idaho have documented only A. fascicularis in that region (Lynn Kinter, Idaho Game and Fish, pers. comm.). Like other southwestern milkweed species with cream flowers (for example, A. nyctaginifolia, A. subulata), tarantula hawk wasps (Pompilidae, Pepsinae) are avid floral visitors to A. subverticillata, in spite of tiny flowers presenting minute quantities of nectar.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 14. FNA vol. 14.
Parent taxa Apocynaceae > Asclepias Apocynaceae > Asclepias
Sibling taxa
A. albicans, A. amplexicaulis, A. angustifolia, A. arenaria, A. asperula, A. brachystephana, A. californica, A. cinerea, A. connivens, A. cryptoceras, A. curassavica, A. curtissii, A. cutleri, A. eastwoodiana, A. elata, A. emoryi, A. engelmanniana, A. eriocarpa, A. erosa, A. exaltata, A. fascicularis, A. feayi, A. hallii, A. hirtella, A. humistrata, A. hypoleuca, A. incarnata, A. involucrata, A. labriformis, A. lanceolata, A. lanuginosa, A. latifolia, A. lemmonii, A. linaria, A. linearis, A. longifolia, A. macrosperma, A. macrotis, A. meadii, A. michauxii, A. nummularia, A. nyctaginifolia, A. obovata, A. oenotheroides, A. ovalifolia, A. pedicellata, A. perennis, A. prostrata, A. pumila, A. purpurascens, A. quadrifolia, A. quinquedentata, A. rubra, A. rusbyi, A. ruthiae, A. sanjuanensis, A. scaposa, A. solanoana, A. speciosa, A. sperryi, A. stenophylla, A. subulata, A. subverticillata, A. sullivantii, A. syriaca, A. texana, A. tomentosa, A. tuberosa, A. uncialis, A. variegata, A. verticillata, A. vestita, A. viridiflora, A. viridis, A. viridula, A. welshii
A. albicans, A. amplexicaulis, A. angustifolia, A. arenaria, A. asperula, A. brachystephana, A. californica, A. cinerea, A. connivens, A. cordifolia, A. cryptoceras, A. curassavica, A. curtissii, A. cutleri, A. eastwoodiana, A. elata, A. emoryi, A. engelmanniana, A. eriocarpa, A. erosa, A. exaltata, A. fascicularis, A. feayi, A. hallii, A. hirtella, A. humistrata, A. hypoleuca, A. incarnata, A. involucrata, A. labriformis, A. lanceolata, A. lanuginosa, A. latifolia, A. lemmonii, A. linaria, A. linearis, A. longifolia, A. macrosperma, A. macrotis, A. meadii, A. michauxii, A. nummularia, A. nyctaginifolia, A. obovata, A. oenotheroides, A. ovalifolia, A. pedicellata, A. perennis, A. prostrata, A. pumila, A. purpurascens, A. quadrifolia, A. quinquedentata, A. rubra, A. rusbyi, A. ruthiae, A. sanjuanensis, A. scaposa, A. solanoana, A. speciosa, A. sperryi, A. stenophylla, A. subulata, A. sullivantii, A. syriaca, A. texana, A. tomentosa, A. tuberosa, A. uncialis, A. variegata, A. verticillata, A. vestita, A. viridiflora, A. viridis, A. viridula, A. welshii
Synonyms Acerates cordifolia, Gomphocarpus cordifolius A. verticillata var. subverticillata
Name authority (Bentham) Jepson: Fl. W. Calif., 384. (1901) (A. Gray) Vail: Bull. Torrey Bot. Club 25: 178. (1898)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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