Asclepias michauxii
Asclepias humistrata
Michaux's milkweed
pinewoods milkweed, sandhill milkweed, sandhill or pinewoods or pink-vein milkweed
1–4 (rarely more), spreading to decumbent or ascending, unbranched, 15–30 cm, minutely puberulent with curved trichomes, not glaucous, rhizomes absent.
1–10, decumbent or ascending to erect, unbranched, 20–50 cm, glabrous, glaucous, rhizomes absent.
opposite or alternate, sessile, often ascending and appearing secund, with 0 or 1 stipular colleter on each side of leaf base;
blade narrowly linear, 4–9 × 0.1–0.4 cm, chartaceous, base cuneate, margins entire, apex acute, venation faintly eucamptodromous to obscure, surfaces glabrous, margins remotely ciliate to glabrate, laminar colleters absent.
opposite, sessile, with 0 or 1 stipular colleter on each side of leaf base;
blade ovate, 4–11 × 2.5–8 cm, subsucculent, base cordate, clasping, margins entire, apex obtuse, mucronulate, venation eucamptodromous to brochidodromous, surfaces glabrous, glaucous, laminar colleters absent.
terminal, sometimes also extra-axillary at upper nodes, sessile or pedunculate, 6–28-flowered;
peduncle 0–4 cm, minutely puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel.
terminal, sometimes branched, and extra-axillary at upper nodes, pedunculate, 7–37-flowered;
peduncle 2.6–5.5 cm, glabrous, glaucous, with 1 bract at the base of each pedicel.
9–12 mm, minutely puberulent on 1 side with curved trichomes.
18–26 mm, glabrous.
erect, calyx lobes narrowly lanceolate, 2.5–3 mm, apex acute, sparsely puberulent with curved trichomes to glabrate;
corolla green to tan, tinged pink or red, inconspicuously striate, lobes reflexed with spreading tips, elliptic, 4–5 mm, apex acute, glabrous;
gynostegial column 0.5–1 mm, fused anthers green, broadly cylindric, 1.5–3 mm, wings narrowly right-triangular, open at tip, apical appendages ovate;
corona segments cream, often pink-striped, to magenta, stipitate, cupulate, margins not strongly incurved, 2.5–3.5 mm, slightly exceeding style apex, apex obtuse, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, glabrous;
style apex shallowly depressed, pale to deep pink.
erect to spreading;
calyx lobes lanceolate, 2–3 mm, apex obtuse, glabrous;
corolla pink or red to pinkish green or reddish green, lobes reflexed, sometimes with spreading tips, oval, 5.5–6 mm, apex acute to obtuse, glabrous;
gynostegial column 0.5–1 mm;
fused anthers brown, cylindric, 1.2–1.5 mm, wings right-triangular, tips closed, apical appendages broadly ovate;
corona segments pink to nearly white at base, white at apex, yellowing with age, sessile, conduplicate, dorsally rounded, 3–3.5 mm, slightly exceeding style apex, base subsaccate, apex truncate with a proximal tooth on each side, glabrous, internal appendage ensiform, slightly incurved, slightly exserted, glabrous;
style apex shallowly depressed, pink.
ovate, 7–8 × 5–6 mm, margin winged, faces smooth;
coma 1.5–2.5 cm.
ovate to oval, 8–8.5 × 5–6 mm, margin winged, faces papillose-rugulose;
coma 3–3.5 cm.
erect on straight pedicels, narrowly fusiform, 7.5–12.5 × 0.5–0.7 cm, apex long-attenuate, smooth, minutely puberulent with curved trichomes.
erect on upcurved pedicels, lance-ovoid, 8–12 × 0.8–1.7 cm, apex long-acuminate to attenuate, smooth, glabrous, glaucous.
Asclepias michauxii
Asclepias humistrata
Asclepias michauxii occurs with, and bears an overall similarity to, A. longifolia. They are distinguished easily in flower by the cavitate corona segments with exserted appendages of A. michauxii. Commonly, A. michauxii has decumbent stems with secund leaves, unlike A. longifolia. In fruit, A. michauxii is distinguished easily by straight pedicels. Like A. longifolia, A. michauxii barely enters Louisiana, east of the Mississippi River (Livingston, Saint Tammany, and Tangipahoa parishes), and is considered to be of conservation concern in that state.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Asclepias humistrata is a distinctive milkweed unlike any other in its range. Its decumbent habit with vertically oriented leaves, bearing strongly contrasting white or pink venation, is unmatched by any other sandhill species. It is apparently closely related to the highly disjunct A. cordifolia of the Pacific Northwest, suggesting an unusual biogeographic history (M. Fishbein et al. 2011). It shares with this species bluish, grayish, or purplish glaucous herbage. Asclepias humistrata often exhibits remarkably high fruit set and, perhaps as a consequence, often grows in large, dense populations. It is reported as possibly extirpated from Louisiana, where it was documented from Washington Parish. Asclepias amplexicaulis Michaux, an illegitimate synonym, created confusion between this species and A. amplexicaulis Smith, a similarly glaucous, cordate-leaved species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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