Asclepias albicans

Shrubs. Stems 5–40 (usually 1–few), erect to ascending, branched, especially in lower half, 140–400 cm, sparsely pilose to glabrate, thickly glau­cous, rhizomes absent. Leaves 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. Inflorescences 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. Pedicels 8–16 mm, pilose. Flowers 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. Follicles spreading to pendulous on spreading to pendulous pedicels, fusiform to lance-ovoid, 5.5–12 × 0.7–1.8 cm, apex acuminate, smooth, pilosulous. Seeds 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.

Phenology: Flowering and fruiting year-round.
Habitat: Mountain slopes, ridge tops, bajadas, flats, arroyos, granite, basalt, tuff, coarse rocky soils, cracks in boulders, sand, desert scrub.
Elevation: 50–800 m.

Distribution

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• Legacy Map

Ariz., Calif., Mexico (Baja California, Baja California Sur, Sonora).

Discussion

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.

Selected References

None.

Lower Taxa

None.