Asclepias cordifolia
Asclepias amplexicaulis
heart-leaf milkweed, purple milkweed
blunt-leaf milkweed, blunt-leaf or clasping or sand milkweed, clasping milkweed
1–20, ascending to spreading, unbranched, 25–100 cm, glabrous, glaucous, rhizomes absent.
1 or 2+, erect, unbranched, 35–175 cm, glabrous, glaucous, rhizomes absent.
opposite, sessile, stipular colleters absent;
blade ovate to lanceolate, 3.5–11 × 1.8–8 cm, chartaceous, base cordate, clasping, margins entire, apex acute, mucronate, venation brochidodromous to eucamptodromous, surfaces glabrous, glaucous, margins minutely ciliate, laminar colleters absent.
opposite, sessile, with 1 stipular colleter on each side of leaf base;
blade broadly ovate or oval to oblong, 6–14 × 3–7 cm, chartaceous, base cordate, clasping, margins often crisped, apex rounded to truncate, emarginate, or obtuse, sometime mucronate, venation eucamptodromous to brochidodromous, surfaces glabrous, glaucous, margins minutely ciliate, 6–16 laminar colleters.
terminal, branched, sometimes also extra-axillary at upper nodes, pedunculate, 5–20-flowered;
peduncle 0.3–6.5 cm, apically sparsely pilose to glabrate, with few bracts.
terminal (extra-axillary at upper nodes), pedunculate, 18–53-flowered;
peduncle occasionally branched, 5–40 cm, glabrous, glaucous, with 1 caducous bract at the base of each pedicel.
16–37 mm, sparsely pilose.
20–55 mm, puberulent with curved trichomes.
erect to pendent;
calyx lobes elliptic to lanceolate, 3–5 mm, apex acute, pilose;
corolla red-violet, lobes reflexed with spreading tips, oval, 6–7 mm, apex acute, glabrous;
gynostegial column 1–1.5 mm;
fused anthers brown, cylindric, 1.5–2 mm, wings right-triangular, open at tip, apical appendages deltoid;
corona segments white, tinged pink to red-violet at base, sessile, tubular, 2–3 mm, exceeded by style apex, base saccate, apex truncate, oblique, glabrous, internal appendage absent;
style apex shallowly depressed, pink to red-violet.
erect to spreading;
calyx lobes narrowly lanceolate, 3–5 mm, apex attenuate, sparsely pilosulous to glabrate;
corolla green, often tinged red, purple, or bronze, lobes reflexed, lanceolate, 8–11 mm, apex acute, glabrous;
gynostegial column 1.5–2.5 mm;
fused anthers green, obconic, 2.5–3.5 mm, wings right-triangular, open at base, apical appendages rhomboid;
corona segments reddish purple to cream, stipitate, tubular, 4–6 mm, exceeding style apex, apex truncate, erose, glabrous, internal appendage falcate, exserted, sharply inflexed over style apex, glabrous;
style apex shallowly depressed, green.
ovate, 8–9 × 5–7 mm, margin not winged, faces reticulate-rugulose;
coma 3–3.5 cm.
ovate, 9–10 × 6–7 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
erect on upcurved pedicels, lance-ovoid, 7.5–10.5 × 1.5–1.8 cm, apex long-acuminate, smooth, glabrous, glaucous.
erect on upcurved pedicels, fusiform to narrowly lance-ovoid, 9–16 × 1–2 cm, apex long-acuminate, smooth, pilosulous.
= 22.
Asclepias cordifolia
Asclepias amplexicaulis
Fresh leaves and stems of Asclepias cordifolia are often slightly or strongly colored bluish, grayish, or purplish. This is one of the few American species of Asclepias with cavitate corona segments that lack adaxial appendages. Such species were segregated along with diverse African species in Gomphocarpus R. Brown, a polyphyletic segregate (M. Fishbein et al. 2011; D. Chuba et al. 2017). Asclepias cordifolia is a distinctive species unlike any other within its range. It is phylogenetically and geographically isolated, although not highly derived morphologically. In Nevada, A. cordifolia is restricted to the Sierra Nevada, in Carson City, Douglas, and Washoe counties. Its range extends to northern California and southwestern Oregon.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The common name sand milkweed refers to a strong association of Asclepias amplexicaulis with sandstone substrates and sandy soils. The clasping leaves and long-peduncled terminal inflorescence of A. amplexicaulis are distinctive among all co-occurring milkweeds. Western populations of A. amplexicaulis, primarily from prairies, usually have paler flowers with creamy coronas, whereas those from forest openings in the eastern and southeastern United States usually have pink to maroon coronas. The species is rare on the northwestern and northeastern margins of its range, where it is considered to be of conservation concern in Minnesota, Nebraska, New Hampshire, Rhode Island, Vermont (only in Chittenden County), and West Virginia. Hybrids with A. exaltata, A. purpurascens, and A. syriaca are known, but are local and not documented often. Presumed hybrids can be recognized by possessing intermediate floral and vegetative characteristics. Asclepias × intermedia Vail probably applies to the hybrid with A. syriaca based on Vail’s protologue (A. M. Vail 1904), but the holotype (E. P. Bicknell s.n. [NY]) is damaged, making the assignment tentative. The homonym A. amplexicaulis Michaux was applied to A. humistrata in the past, resulting in some taxonomic confusion between these species and the misidentification of herbarium specimens.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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