Asclepias brachystephana
Asclepias engelmanniana
bract milkweed, short-crowned milkweed, shortcrown milkweed
Engelmann's milkweed
4–25, erect, unbranched or branched near base, 20–40 cm, tomentulose, not glaucous, rhizomes absent.
1 or 2 (rarely more), erect, sometimes branched, 40–160 cm, glabrous, not glaucous, rhizomes absent.
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.
alternate, sessile, drooping, with 1 stipular colleter on each side of leaf base;
blade linear, conduplicate, 5–19 × 0.15–0.3 cm, chartaceous, base cuneate, margins entire, apex acute, venation faintly brochidodromous to obscure, surfaces sparsely puberulent with curved trichomes 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, sessile or pedunculate, 14–23-flowered;
peduncle occasionally branched, 0–2 cm, pilosulous or puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel.
9–15 mm, tomentose.
8–11 mm, pilose.
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 spreading;
calyx lobes lanceolate, 3–4 mm, apex acute, pilosulous;
corollas tan to russet abaxially, pale green to greenish cream or ochroleucous to tan adaxially, lobes reflexed with ascending tips, elliptic, 4–5 mm, apex acute, glabrous;
gynostegial column 0.5–1.5 mm;
fused anthers brown, broadly barrel-shaped, 2–2.5 mm, wings crescent-shaped and narrowly open throughout, apical appendages narrowly pandurate, conduplicate, not obscuring corpuscula;
corona segments cream to tan or yellow, sessile, chute-shaped, 2–3 mm, equaling style apex, base saccate and auriculate, apex retuse to nearly truncate, glabrous, internal appendage absent or obscure, glabrous;
style apex depressed, green to yellowish green.
oval to ovate, 6–7 × 4–6 mm, margin winged, faces papillate-tomentulose with dendritic scales;
coma 2–2.5 cm.
ovate, 8–9 × 5–6 mm, margin winged, faces minutely papillose and rugulose;
coma 2–2.5 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, 6–10 × 1.2–2 cm, apex long-acuminate, smooth, pilosulous.
Asclepias brachystephana
Asclepias engelmanniana
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 engelmanniana is usually a tall herb with drooping leaves and spherical umbels of greenish yellow flowers rising above surrounding grassland plants. In spite of its distinctive appearance, it is quite similar to its close relatives, A. rusbyi and A. stenophylla. The yellowish green coronas, squat flowers, upcurved fruiting pedicels, and drooping leaves distinguish A. engelmanniana from A. stenophylla, which has more slender flowers with creamy coronas, straight pedicels in fruit, and spreading to ascending leaves. Despite ranges with only little overlap and few if any mixed populations, these two species are often confused, especially in the absence of flowers. Compared to its close relative, A. engelmanniana is distributed further west, in mixed- and short-grass prairies. A report of A. engelmanniana from South Dakota has not been confirmed, and reports from Iowa appear to have been based on misidentified specimens of A. stenophylla. Reports from Arkansas are unconfirmed and also very likely to be based on misidentifications. Asclepias engelmanniana is considered to be of conservation concern in Wyoming, where it has been recorded only from Goshen County. Asclepias rusbyi has been inconsistently distinguished from A. engelmanniana (for example, E. Sundell 1994), although the differences elucidated by R. E. Woodson Jr. (1954) are sound. These species are readily distinguished by the characters in the key and appear to have allopatric ranges. Reports of A. engelmanniana from Arizona, western New Mexico, Nevada, Utah, southwestern Colorado, and Sonora, Mexico, all pertain to A. rusbyi.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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