Asclepias albicans
Asclepias latifolia
candelilla, wax milkweed, white-stem milkweed
broad-leaf milkweed, corn-kernel 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, 25–100 cm, puberulent with curved trichomes or thinly tomentose to glabrate, sometimes 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.
opposite, sessile or petiolate, with 1–4 stipular colleters on each side of petiole, sometimes also in axil;
petiole 0–4 mm, thinly tomentose to glabrate;
blade oval or oblong to ovate or orbiculate, 5.5–14 × 3–14 cm, subsucculent to coriaceous, base cordate, sometimes clasping, margins entire, apex truncate to rounded, sometimes emarginate, mucronate, venation brochidodromous, surfaces thinly tomentose to glabrate, sometimes glaucous, margins minutely ciliate to glabrous, 24–80 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, sessile or pedunculate, 20–59-flowered;
peduncle 0–2.5 cm, puberulent with curved trichomes to pilosulous, with 1 caducous bract at the base of each pedicel.
8–16 mm, pilose.
15–35 mm, densely 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, 4–5 mm, apex acute, tomentose to glabrate;
corolla green, lobes reflexed, elliptic to oval, 7–9 mm, apex acute, glabrous abaxially, papillose at base adaxially;
gynostegial column 1–1.5 mm;
fused anthers green, cylindric, 3–3.5 mm, wings right-triangular, closed, apical appendages ovate;
corona segments cream, sometimes dorsally yellow, aging yellow, stipitate, conduplicate, dorsally rounded, 3–5.5 mm, equaling to slightly exceeding style apex, apex truncate, oblique, papillose, internal appendage falcate, exserted, sharply inflexed over style apex, papillose;
style apex shallowly depressed, 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, 7–8 × 5–6 mm, winged, faces minutely rugulose to smooth;
coma 3–4 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.
erect on upcurved pedicels, ovoid, 6.5–9.5 × 2–3 cm, apex obtuse to apiculate, smooth, minutely pilosulous to thinly tomentulose.
= 22.
Asclepias albicans
Asclepias latifolia
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 latifolia is a distinctive species of the western Great Plains and Colorado Plateau, rising above short grasses and appearing as squat, leafy pagodas. It is most likely to be confused with A. arenaria (which is restricted to sandy substrates) due to the overlapping leaf shapes and floral colors of these species. Asclepias latifolia favors clayey, often rocky soils, but can be found also on sandy soils, especially on the Colorado Plateau, outside the range of A. arenaria. These species can be distinguished by habit (erect in A. latifolia versus erect to decumbent in A. arenaria), vestiture (more uniformly and persistently hairy in A. arenaria), petioles (absent or nearly so in A. latifolia versus present in A. arenaria), and the flower and seed characters included in the key. Asclepias speciosa in the absence of reproductive structures is also commonly confused with A. latifolia, but the leaves of A. speciosa are distinctly petiolate, persistently hairy, and typically taper to the apex. There is an apparent gap in the distribution of A. latifolia on the eastern Colorado Plateau, in northwestern New Mexico and southwestern Colorado, but the disjunct portions of the range are not accompanied by phenotypic divergence. Asclepias latifolia is limited in Nebraska to southwestern counties (Deuel, Dundy, Franklin, and Hayes), but it is apparently not uncommon there. Likewise, it is common in its limited range in Utah (Garfield, Grand, Kane, San Juan, and Wayne counties).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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