Asclepias texana
Asclepias uncialis
Texas milkweed
dwarf milkweed, wheel milkweed
1–numerous, erect, sparsely to moderately branched in upper half, 25–90 cm, puberulent with curved trichomes in a line, not glaucous, rhizomes absent.
1–13, decumbent, unbranched or branched near base, 4–10 cm, puberulent with curved trichomes, not glaucous, rhizomatous.
opposite, petiolate, with 1 or 2 stipular colleters on each side of petiole on a ciliate interpetiolar ridge;
petiole 5–20 mm, puberulent with curved trichomes;
blade ovate to lanceolate or elliptic, 2–7 × 0.5–3 cm, chartaceous, base cuneate to obtuse, margins entire, apex acute to acuminate, venation eucamptodromous, surfaces puberulent with curved trichomes on veins abaxially, sparsely puberulent with curved trichomes on veins to glabrate adaxially, margins ciliate, laminar colleters absent.
opposite and alternate, petiolate, with 1 stipular colleter on each side of petiole;
petiole 1–5 mm, puberulent with curved trichomes to pilosulous;
blade linear to lanceolate, 1.7–5 × 0.2–1 cm, chartaceous, base cuneate, margins entire, apex attenuate, venation obscure, surfaces puberulent on midvein with curved trichomes, margins densely ciliate, laminar colleters absent.
extra-axillary at upper nodes, some appearing terminal, pedunculate, 14–31-flowered;
peduncle 0.9–3 cm, puberulent with curved trichomes in a line, with 1 caducous bract at the base of each pedicel.
terminal and extra-axillary at upper nodes, sessile, 3–7-flowered, bracts few.
7–14 mm, puberulent with curved trichomes in a line.
10–18 mm, densely puberulent with curved trichomes.
erect;
calyx lobes narrowly lanceolate, 1.5–2 mm, apex acute, puberulent with curved trichomes;
corolla white, sometimes tinged green, lobes reflexed with spreading tips, elliptic, 3.5–5 mm, apex acute to obtuse, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers brown, columnar, 1.5–2 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments white, sometimes tinged pink, stipitate, cupulate, dorsally rounded, 2–3 mm, equaling to slightly exceeding style apex, apex obtuse, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous;
style apex shallowly depressed, white.
erect;
calyx lobes elliptic, 2–2.5 mm, apex acute, puberulent with curved trichomes;
corolla red-violet, lobes reflexed with spreading tips, oval, 3–5 mm, apex acute, glabrous;
gynostegial column 0.2–0.5 mm;
fused anthers brown, cylindric, 1–1.5 mm, wings narrowly right-triangular, apical appendages ovate, erose;
corona segments red-violet dorsally, white to orange proximally, sessile, cupulate, 1–2 mm, exceeded by style apex, apex truncate with a proximal tooth on each side, glabrous, internal appendage lingulate, barely exserted from cavity, glabrous;
style apex shallowly depressed, pink to red-violet.
ovate, 6–7 × 4–5 mm, margin winged, faces smooth or sparsely papillose;
coma 2–3 cm.
broadly ovate, 7–8 × 5–6 mm, margin winged, erose, faces rugulose, lepidote;
coma 1.5–2 cm.
erect on straight pedicels, narrowly fusiform, 9–13 × 0.5–1 cm, apex long-acuminate to attenuate, smooth, glabrous.
erect on upcurved pedicels, ovoid, 3–5 × 0.8–1.5 cm, apex acuminate, smooth, minutely puberulent with curved trichomes.
Asclepias texana
Asclepias uncialis
In the flora area, Asclepias texana has a disjunct distribution on the Edwards Plateau and in the mountains of the Big Bend region. Although commonly occurring in canyons and riparian areas, A. texana is quite drought tolerant in cultivation. The tidy, bushy habit, long flowering stems topped by bright white spherical umbels, and rapid growth from seed make this a suitable candidate for horticultural use. It is known to be hardy to at least USDA Zone 7.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias uncialis is by far the most widespread of the four diminutive, red-violet-petaled milkweeds of western North America (species 57–60). It typically has much narrower leaves than the other three species, and is extraordinarily cryptic in the absence of flowers in its characteristic short-grass prairie habitat, where its leaves closely mimic dominant grama grasses, particularly Bouteloua gracilis. Although it is widespread, it is encountered commonly only in southeastern Colorado and has only been recorded at single sites in Oklahoma (Cimarron County) and Texas (Andrews County), where the species should be considered to be of conservation concern. It is considered to be of concern in Colorado and New Mexico, but it is possible that this cryptic species is more common than has been recorded. Nonetheless, it appears that it has declined in northern Colorado. An 1873 specimen (C. C. Parry 246 [GH]) from Wyoming is the only documented record from that state and is from a highly disjunct location (attributed to Sweetwater County). It is possible that the reported location was in error; otherwise, it appears that A. uncialis has been extirpated from Wyoming, which is excluded from the range of the species in this treatment.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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