Asclepias brachystephana
Asclepias albicans
bract milkweed, short-crowned milkweed, shortcrown milkweed
candelilla, wax milkweed, white-stem milkweed
4–25, erect, unbranched or branched near base, 20–40 cm, tomentulose, not glaucous, rhizomes absent.
5–40 (usually 1–few), erect to ascending, branched, especially in lower half, 140–400 cm, sparsely pilose to glabrate, thickly 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.
ephemeral, rarely present on flowering stems, opposite, sessile, with 0 or 1 stipular colleter on each side of leaf base;
blade filiform, 1.5–2.5 × 0.1 cm, succulent, base cuneate, margins entire, apex acute, mucronate, venation obscure, surfaces pilosulous, 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.
terminal, branched, also extra-axillary at leafless upper nodes, pedunculate, 8–50-flowered;
peduncle 0.2–4.5 cm, pilose, with 1 caducous bract at the base of each pedicel.
9–15 mm, tomentose.
8–16 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 pendent;
calyx lobes lanceolate to linear-lanceolate, 2.5–3 mm, apex acute, densely pilose;
corolla ochroleucous to greenish cream, sometimes tinged red, faintly striate, lobes reflexed or sometimes spreading, oval, 4.5–6 mm, apex acute, glabrous;
gynostegial column 1–1.8 mm;
fused anthers brown, cylindric, 1.8–2 mm, wings right-triangular, closed, apical appendages ovate, erose;
corona segments cream, often tinged pink, yellow, or green, shiny, sessile, conduplicate, 2–3 mm, exceeded by style apex, base saccate, apex truncate, oblique, glabrous, internal appendage falcate, exserted, sharply inflexed towards style apex, densely papillate;
style apex shallowly depressed, ochroleucous to green.
oval to ovate, 6–7 × 4–6 mm, margin winged, faces papillate-tomentulose with dendritic scales;
coma 2–2.5 cm.
naviculate, lanceolate, 5–7 × 2.5–3 mm, margin narrowly winged, faces papillose and rugulose, concave face with a low keel;
coma 1.5–2 cm.
erect on upcurved pedicels, lance-ovoid, 5–7 × 1.2–1.8 cm, apex acuminate, shallowly ribbed, conspicuously striate, tomentulose.
spreading to pendulous on spreading to pendulous pedicels, fusiform to lance-ovoid, 5.5–12 × 0.7–1.8 cm, apex acuminate, smooth, pilosulous.
Asclepias brachystephana
Asclepias albicans
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 albicans reaches the greatest height of any Asclepias species in the flora area and among congeners can be confused only with A. subulata, the only other shrubby, leafless milkweed in the region. In the absence of flowers, it may be difficult to distinguish these species. In addition to the key characters, A. albicans often differs by thicker, waxier stems. The species are also ecologically divergent: A. albicans is most commonly found on rocky slopes and ridges (usually basalt or granite), and A. subulata is usually found on flats and in arroyos, often in sandy soils. However, A. albicans can occur on bajadas and in arroyos, often distant from the mountains and ridges harboring source populations. These species have extensively overlapping ranges but rarely hybridize at widely scattered locations in Arizona, California, and Baja California Sur. Hybrids are identified by intermediate floral morphology, especially corona size and shape. The range of A. albicans is within the limits of the Sonoran Desert. In Arizona, it is found in La Paz, Maricopa, Mohave, Pima, Pinal, and Yuma counties; in California only in Imperial, Riverside, San Bernardino, and San Diego counties.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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