Asclepias michauxii
Asclepias asperula
Michaux's milkweed
Antelope horns, spider milkweed
1–4 (rarely more), spreading to decumbent or ascending, unbranched, 15–30 cm, minutely puberulent with curved trichomes, not glaucous, rhizomes absent.
1–40, erect to decumbent, unbranched or branched at base, 15–60 cm, puberulent with curved trichomes, not 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.
alternate to subopposite, petiolate, with 1–3 stipular colleters on each side of petiole;
petiole 2–4 mm, puberulent with curved trichomes to pilosulous;
blade lanceolate to linear, 5–17 × 0.4–3.7 cm, chartaceous, base cuneate, margins entire, apex attenuate to acute, mucronate, venation eucamptodromous to brochidodromous, surfaces puberulent with curved trichomes to glabrate, more densely so on veins, margins ciliate, 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, sessile or pedunculate, 10–60-flowered;
peduncle 0–22.5 cm, puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel.
9–12 mm, minutely puberulent on 1 side with curved trichomes.
16–30 mm, puberulent with curved trichomes to pilose.
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 ovate to linear-lanceolate, 3–5 mm, apex acute, pilosulous to puberulent with curved trichomes;
corolla pale green, sometimes tinged red abaxially, campanulate, lobes ascending and exceeding corolla segments, ovate to oval, 7–10 mm, apex acute, puberulent with curved trichomes at apex abaxially, glabrous adaxially;
gynostegium sessile;
fused anthers brown and green, turbinate, 2–2.5 mm, wings trapezoidal, widest above middle, closed, apical appendages ovate, erose;
corona segments reddish purple and white, sessile, clavate-tubular, 4.5–7 mm, slightly exceeded by to equaling style apex, deflexed at base, margins connivent, apex incurved, rounded, upper margin and cavity papillose, internal appendage a low internal crest, papillose;
style apex depressed, green.
ovate, 7–8 × 5–6 mm, margin winged, faces smooth;
coma 1.5–2.5 cm.
ovate, 5–8 × 4–6 mm, margin winged, remotely erose, faces minutely rugulose-papillose, minutely hirtellous;
coma 2.5–4 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, 6–11.5 × 1–2.5 cm, apex short- to long-acuminate, weakly to strongly arcuate, shallowly rugose-ribbed, ribs sometimes muricate, striate, pilosulous.
Asclepias michauxii
Asclepias asperula
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.)
Subspecies 2 (2 in the flora).
With terminal umbels of large, green and purple flowers, Asclepias asperula is highly distinctive and in flower can be confused only with its sister species, A. viridis. Distinguishing characteristics and the existence of interspecific hybrids are discussed under A. viridis. Large bees, notably Bombus and Xylocopa, are commonly observed visiting the flowers of A. asperula.
The subspecies of Asclepias asperula are strongly differentiated away from their region of contact, which extends from south of the Texas Panhandle to the extreme tip of the Oklahoma Panhandle. In the region of contact, their distinguishing traits intermix. The common occurrence of intermediates and apparent introgressants argues against elevation of the subspecies to the specific rank. There is a surprising gap in the distribution of the species as a whole on the Llano Estacado in eastern New Mexico and the Texas Panhandle that may contribute to the differentiation of the subspecies.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Corona segments reddish purple with white upper margin, 5–7 mm; follicle ribs inconspicuously muricate at apex or not at all. | subsp. asperula |
1. Corona segments white, dorsally reddish purple, 4.5–6 mm; follicle ribs sparsely to densely muricate for most of the length. | subsp. capricornu |
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