Asclepias curassavica
Asclepias subverticillata
blood flower, bloodflower milkweed, hierba de la cucaracha, tropical milkweed, wild ipecacuanha
horsetail milkweed, poison milkweed, western whorled or horsetail or poison or whorled milkweed
1–several, erect, sparsely to moderately branched, 30–150 cm, minutely pilosulous in a line to glabrate, not 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.
persistent or gradually caducous from the base, opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole on a ciliate interpetiolar ridge;
petiole 4–25 mm, puberulent with curved trichomes in a line to glabrate;
blade elliptic or oval to linear, 4–18 × 0.3–4.5 cm, membranous, base cuneate, margins entire, apex acute to acuminate to attenuate, venation eucamptodromous to faintly brochidodromous, surfaces sparsely puberulent with curved trichomes on veins abaxially, sparsely puberulent with curved trichomes on veins to glabrate adaxially, margins 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.
extra-axillary, pedunculate, 5–22-flowered;
peduncle 0.5–8 cm, puberulent with curved trichomes in a line, with 1 caducous bract at the base of each pedicel.
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.
7–20 mm, puberulent with curved trichomes.
5–12 mm, puberulent with curved trichomes.
erect;
calyx lobes linear-lanceolate, 3–4 mm, apex acute, puberulent with curved trichomes;
corolla red, sometimes yellow in throat (to wholly orange or yellow in cultivars), lobes reflexed with spreading tips, elliptic to oval, 6–9 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 2–2.5 mm;
fused anthers yellowish green to tan, cylindric, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments yellow to orange, stipitate, tubular, dorsally somewhat flattened, 3.5–4 mm, exceeding style apex, apex obtuse to acute, glabrous, internal appendage falcate, exserted, arching over style apex, glabrous;
style apex shallowly depressed, yellow.
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.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose to smooth;
coma 2.5–3 cm.
ovate, 5–8 × 3.5–5 mm, margin winged, faces smooth;
coma 2–2.5 cm.
erect on straight pedicels, fusiform, 6–10 × 0.5–1.2 cm, apex acuminate to attenuate, smooth, glabrous.
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.
= 22.
Asclepias curassavica
Asclepias subverticillata
Asclepias curassavica is the only non-native Asclepias species naturalized in the flora area. It is very commonly cultivated, originally for its strikingly colored flowers and their attraction of Lepidoptera and Hymenoptera. Recently, they have been valued also as a host plant for monarch butterflies. Cultivars with pure orange or pure yellow flowers are readily available. The species develops rapidly from seed and can be grown as an annual (in the horticultural sense) anywhere in the region. Though often described as an annual, like all species of Asclepias, it has a perennial habit. It may persist through mild winters at least as far north as Oklahoma but has only become established in frost-free areas of the southern United States.
(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.)
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