Asclepias brachystephana
Asclepias linearis
bract milkweed, short-crowned milkweed, shortcrown milkweed
slim milkweed
4–25, erect, unbranched or branched near base, 20–40 cm, tomentulose, not glaucous, rhizomes absent.
1–4, erect, often branched, arrested vegetative branches absent, 30–75 cm, puberulent with curved trichomes in lines, not glaucous, rhizomatous.
opposite to subopposite, petiolate, with 1 or 2 stipular colleters on each side of petiole;
petiole 2–8 mm, tomentulose;
blade linear-lanceolate, 5–15 × 0.3–1.3 cm, chartaceous, base cuneate to rounded, margins often obscurely crisped, apex acute, mucronate, venation brochidodromous, surfaces tomentulose to glabrate, midvein puberulent with curved trichomes, margins minutely ciliate, laminar colleters absent.
opposite, sessile, with 1 or 2 stipular colleters on each side of leaf base on a ciliate interpetiolar ridge;
blade linear, 3–8 × 0.1–0.3 cm, chartaceous, base cuneate, margins entire, apex acute, mucronate, venation obscure, surfaces glabrous abaxially, puberulent with curved trichomes adaxially, especially on midvein, to glabrate, margins ciliate, laminar colleters absent.
extra-axillary, pedunculate, 4–15-flowered;
peduncle 0.2–1.5 cm, tomentose, with 1 caducous bract at the base of each pedicel.
extra-axillary at upper nodes, pedunculate, 7–20-flowered;
peduncle 1–1.5 cm, puberulent with curved trichomes on 1 side, with 1 caducous bract at the base of each pedicel.
9–15 mm, tomentose.
6–8 mm, puberulent with curved trichomes on 1 side.
erect;
calyx lobes ovate-lanceolate, 2–3 mm, apex acute, tomentulose;
corolla red-violet, sometimes green with red tinge, lobes reflexed, ovate, 4–6 mm, apex acute, minutely pilosulous;
gynostegium subsessile;
fused anthers brown, cylindric, 2–2.5 mm, wings right-triangular, closed, apical appendages ovate;
corona segments red-violet to pink basally, white apically, sessile, tubular, 1.5–2 mm, greatly exceeded by style apex, apex truncate, oblique, with a proximal tooth on each side, glabrous, internal appendage lingulate, slightly exserted, sharply inflexed towards gynostegium, glabrous;
style apex shallowly depressed, red-violet.
erect to pendent;
calyx lobes linear-lanceolate, 1.5 mm, apex acute, pilosulous;
corolla green, tan, or pink, tinged red or brown, lobes reflexed with spreading tips, elliptic, 3–4 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1–1.2 mm;
fused anthers green, columnar, 1.2–1.5 mm, wings narrowly right-triangular, closed, apical appendages deltoid;
corona segments cream, stipitate, cupulate, dorsally flattened, 1.5 mm, exceeded by style apex, apex rounded, margin with a proximal tooth, glabrous, internal appendage acicular, exserted, arching over style apex, glabrous;
style apex shallowly depressed, cream.
oval to ovate, 6–7 × 4–6 mm, margin winged, faces papillate-tomentulose with dendritic scales;
coma 2–2.5 cm.
ovate, 6–7 × 4–5 mm, margin winged, faces smooth;
coma 2–3 cm.
erect on upcurved pedicels, lance-ovoid, 5–7 × 1.2–1.8 cm, apex acuminate, shallowly ribbed, conspicuously striate, tomentulose.
erect on straight pedicels, narrowly fusiform, 5–8.5 × 0.4–0.7 cm, apex acuminate to attenuate, smooth, sparsely pilosulous to glabrate.
Asclepias brachystephana
Asclepias linearis
Asclepias brachystephana is a blue-gray, bushy herb with ascending foliage, few-flowered umbels of small, red and white flowers, and conspicuously striped follicles. It is unlike any other milkweed. Nonetheless, herbarium specimens are commonly confused with those of A. asperula because the herbage of A. brachystephana turns green on drying, and the leaves of A. asperula subsp. asperula are often of similar size and shape. However, leaf arrangement in A. asperula is alternate rather than opposite. The flowers of A. brachystephana are remarkably similar to, and convergent with, those of A. cutleri, A. eastwoodiana, A. ruthiae, A. sanjuanensis, and A. uncialis (M. Fishbein et al. 2011). In Arizona, A. brachystephana is restricted to the portion of the southeastern corner of the state with Chihuahuan floristic affinities, in Cochise, Graham, Pima, and Santa Cruz counties.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Although the range of Asclepias linearis is quite restricted, it is very common in grassland habitats on the coastal plain of southeastern Texas. Disjunct populations occur in the Dallas-Fort Worth area. It is similar in most respects to A. verticillata with the normally whorled leaves of that species the most reliable character distinguishing it from A. linearis. Although the ranges of these species overlap in the vicinity of Houston and Dallas-Fort Worth, and mixed populations have been reported, putative hybrids have not been documented, although they would be difficult to discern.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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