Asclepias texana
Asclepias sperryi
Texas milkweed
sperry's 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.
few–numerous, erect to ascending, branched at base, 5–20 cm, minutely puberulent with curved trichomes to glabrate, 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, sessile, with 1 stipular colleter on each side of leaf base;
blade filiform, 2–5 × 0.05–0.1 cm, membranous, base cuneate, margins revolute, apex acute, mucronate, venation obscure, surfaces glabrous, margins minutely ciliate at base, 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.
extra-axillary, sessile, 1–2-flowered, with 1 caducous bract at the base of each pedicel.
7–14 mm, puberulent with curved trichomes in a line.
4–10 mm, minutely puberulent with curved trichomes in a line.
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 ovate, 2–3 mm, apex acute, glabrous;
corolla pale greenish yellow tinged with purple, lobes spreading, ovate, 4–5 mm, apex acute, glabrous;
gynostegium sessile;
fused anthers brown, cylindric, 1.5–2 mm, wings deltoid, apical appendages broadly ovate;
corona segments pale greenish yellow to white (sometimes tinted purple), sessile, chute-shaped, sharply inflexed, 2–3 mm, equaling to exceeded by style apex, apex truncate, subcaudate, hirtellous, internal appendage an included crest, hirtellous;
style apex shallowly depressed, green.
ovate, 6–7 × 4–5 mm, margin winged, faces smooth or sparsely papillose;
coma 2–3 cm.
ovate, 5–6 × 3–4 mm, margin thickly winged, faces rugulose;
coma 2–2.5 cm.
erect on straight pedicels, narrowly fusiform, 9–13 × 0.5–1 cm, apex long-acuminate to attenuate, smooth, glabrous.
erect on upcurved pedicels, fusiform, 5–7 × 0.5–0.7 cm, apex attenuate, smooth, glabrous.
Asclepias texana
Asclepias sperryi
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 sperryi is one of the least known milkweeds. It is exceedingly cryptic and easily mistaken for a small clump of grass, perhaps of Bouteloua; it is likely to be far more common than documented. However, very few observations or collections have been made in recent decades, and conservation assessment is warranted. Its range is restricted to limestone mountains of the Chihuahuan Desert in the Big Bend region of Texas, in Brewster and Pecos counties, and adjacent areas of Coahuila, entirely within the range of its sister species, A. macrotis. It is the only species of Asclepias that regularly produces a single flower per umbel.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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