Asclepias brachystephana
Asclepias arenaria
bract milkweed, short-crowned milkweed, shortcrown milkweed
sand milkweed
4–25, erect, unbranched or branched near base, 20–40 cm, tomentulose, not glaucous, rhizomes absent.
1–8, spreading or decumbent to erect, unbranched or rarely branched near base, 20–100 cm, tomentose, 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, petiolate, with 1 or 2 stipular colleters on each side of petiole plus 0–4 in axil;
petiole 7–17 mm, tomentose;
blade oblong or obovate to ovate or oval, 4.2–11.5 × 2.5–7.5 cm, subcoriaceous, base rounded or truncate to subcordate, margins often undulate or crisped, apex truncate to rounded (rarely acute), sometimes emarginate, often mucronate, venation brochidodromous, surfaces tomentose to nearly glabrate, margins ciliate, 12–24 laminar colleters.
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 (sometimes appearing terminal), sessile or pedunculate, 14–51-flowered;
peduncle 0–2 cm, tomentose, with 1 caducous bract at the base of each pedicel.
9–15 mm, tomentose.
15–25 mm, densely tomentose.
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 lanceolate, 2.5–3 mm, apex acute, densely tomentose;
corolla green to yellowish green, sometimes tinged reddish or purplish, lobes reflexed with spreading tips, oval, 7–8 mm, apex acute, glabrous abaxially, minutely papillose at base adaxially;
gynostegial column 1–2 mm;
fused anthers green, obconic, 2–2.5 mm, wings right-triangular, closed, apical appendages ovate;
corona segments cream to greenish cream or ochroleucous, subsessile, conduplicate, flaring at base, 3.5–4 mm, exceeding style apex, apex truncate to rounded, emarginate, minutely papillate, proximal margin toothed, internal appendage falcate, exserted, sharply incurved over style apex, apex upturned, minutely papillose.
oval to ovate, 6–7 × 4–6 mm, margin winged, faces papillate-tomentulose with dendritic scales;
coma 2–2.5 cm.
oval, 9–12 × 6–8 mm, margin winged, faces minutely rugulose;
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 upcurved pedicels, lance-ovoid, 5.5–10 × 2–2.8 cm, apex acuminate, smooth, pilosulous.
Asclepias brachystephana
Asclepias arenaria
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.)
Asclepias arenaria is the milkweed most consistently associated with pure sand soils in the western Great Plains. It is predictably found at the bases of stabilized and semi-stabilized dunes. Flowers of this species are visited by a variety of Hymenoptera, notably several species of large wasps, including tarantula hawk wasps (Pepsinae, Pompilidae) and scoliid wasps (Scoliidae), as well as by Lepidoptera. Non-flowering shoots of A. arenaria may produce linear leaves; they are easily overlooked and not identified as belonging to this species unless one is aware of this variation, especially when they are produced on rhizomes distant from shoots with typical foliage. This trait is found in several other broad-leaved milkweeds (for example, A. erosa, A. welshii). Asclepias arenaria is rare and considered to be of conservation concern in Wyoming, where it has been recorded from only two sites in Goshen County.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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