Asclepias albicans
Asclepias labriformis
candelilla, wax milkweed, white-stem milkweed
Utah milkweed, Utah or labriform or Jones' or poison milkweed
5–40 (usually 1–few), erect to ascending, branched, especially in lower half, 140–400 cm, sparsely pilose to glabrate, thickly glaucous, rhizomes absent.
1–10, erect, unbranched (rarely distally), 15–70 cm, sparsely puberulent with curved trichomes to glabrate, not glaucous, rhizomatous.
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.
alternate (subopposite), sessile or petiolate, with 1 or 2 stipular colleters on each side of petiole plus 4–8 in axil;
petiole 0–7 mm, glabrous;
blade linear-lanceolate to lanceolate, often falcate, 6–14.5 × 0.5–2 cm, chartaceous, base cuneate, margins entire, apex attenuate to acute, mucronate, venation brochidodromous (often faintly), surfaces glabrous, midvein sometimes sparsely puberulent with curved trichomes abaxially, margins eciliate, 0–12 laminar colleters.
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.
extra-axillary, pedunculate, 6–28-flowered;
peduncle 0.2–2.5 cm, tomentose to glabrate, with 1 caducous bract at the base of each pedicel.
8–16 mm, pilose.
15–25 mm, tomentose to glabrate.
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.
erect to pendent;
calyx lobes lanceolate, 3–4 mm, apex acute, sparsely pilose or tomentulose to glabrate;
corolla ochroleucous, lobes reflexed, tips sometimes spreading, oval to elliptic, 6–7 mm, apex acute, glabrous abaxially, minutely hirtellous at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers green to yellowish green, obconic, 1.5–2 mm, wings narrowly right-triangular, tip distended, closed, apical appendages ovate;
corona segments ochroleucous to cream, substipitate, conduplicate, dorsally rounded, nearly tubular, 2.5–3.5 mm, slightly exceeding style apex, apex truncate with proximal tooth on each side, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, glabrous;
style apex shallowly depressed, cream or green.
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.
ovate to oval, 12–13 × 8–9 mm, margin winged, faces obscurely rugulose to smooth;
coma 1.5–2 cm.
spreading to pendulous on spreading to pendulous pedicels, fusiform to lance-ovoid, 5.5–12 × 0.7–1.8 cm, apex acuminate, smooth, pilosulous.
pendulous on spreading to pendulous pedicels, ovoid, 3.5–5.5 × 1.2–2 cm, apex acuminate, smooth, tomentulose to glabrate.
Asclepias albicans
Asclepias labriformis
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.)
Asclepias labriformis is endemic to Utah (Emery, Garfield, Grand, Uintah, and Wayne counties) and is found in a remarkably narrow northeast–southwest band from the terraces surrounding the San Rafael Swell west of Green River, across Waterpocket Fold, to arroyo beds below the Kaiparowits Plateau southeast of Escalante. It shares pendulous follicles with several other milkweed species inhabiting sandy habitats, such as its close relative A. welshii, and more distant relatives A. cutleri and A. subulata. Asclepias labriformis is reputed to be one of the milkweeds that is most poisonous to livestock (J. M. Benson et al. 1979).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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