Asclepias stenophylla
Asclepias cinerea
narrow-leaf milkweed, slimleaf milkweed
ashy milkweed, Carolina milkweed
1 or 2 (rarely more), erect to spreading, rarely branched, 15–85 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
1, erect, unbranched (rarely branched), 20–100 cm, minutely puberulent in a line with curved trichomes to glabrate, not glaucous, rhizomes absent.
alternate, subopposite, or opposite, sessile or petiolate, with 1 stipular colleter on each side of petiole;
petiole 0–1 mm, spreading to ascending, glabrate;
blade linear, conduplicate, 5–16 × 0.1–0.5 cm, chartaceous, base cuneate, margins entire, apex acute, venation faintly brochidodromous to obscure, surfaces sparsely puberulent with curved trichomes, especially on midvein, to glabrate, margins ciliate, laminar colleters absent.
opposite, sessile, with 1 or 2 stipular colleters on each side of leaf base;
blade filiform, 2–9 × 0.1–0.15 cm, membranous, base cuneate, margins entire, apex acute, mucronate, venation obscure, surfaces glabrous, laminar colleters absent.
extra-axillary, sessile or pedunculate, 9–28-flowered;
peduncle 0–1.3 cm, sometimes branched at apex, puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel.
terminal, branched, and extra-axillary at upper nodes, pedunculate, 2–8-flowered;
peduncle 0.5–1.7 cm, puberulent with curved trichomes on 1 side, with 1 caducous bract at the base of each pedicel.
5–12 mm, puberulent with curved trichomes to pilosulous.
10–25 mm, minutely puberulent with curved trichomes on 1 side.
erect to pendent;
calyx lobes lanceolate, 1.5–2.5 mm, apex acute, puberulent with curved trichomes to pilosulous;
corolla pale green to greenish cream, lobes reflexed with spreading tips, elliptic, 3–5 mm, apex acute, minutely puberulent with curved trichomes at apex abaxially, glabrous adaxially;
gynostegial column 0–0.5 mm, fused anthers green, truncately obconic, 1.5–2 mm, wings narrowly crescent-shaped, wide open at base, apical appendages deltoid;
corona segments cream, often green-tinged, sessile, chute-shaped, margins incurved, appressed to anthers, 3–3.5 mm, equaling style apex, base saccate, auriculate, apex truncate, glabrous, internal appendage a short crest, the segment appearing 3-toothed, glabrous;
style apex shallowly depressed, green.
spreading to pendent;
calyx lobes lanceolate, 1.5–2 mm, apex acute, glabrous;
corolla cream, tinged gray, pink, or purple, faintly striate, lobes reflexed with spreading tips, elliptic, 4–5 mm, apex acute to obtuse, glabrous;
gynostegial column 0–0.5 mm;
fused anthers green, cylindric, 1.5–2 mm, wings narrowly right-triangular, open, apical appendages deltate;
corona segments cream, tinged gray, pink, or purple, sessile, conduplicate, dorsally flattened, 2–3 mm, equaling style apex, apex truncate with a proximal tooth on each side, glabrous, internal appendage a laterally flattened, included crest, glabrous;
style apex shallowly depressed, white.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
ovate, 6–7 × 4–5 mm, margin thickly winged, faces sparsely papillose;
coma 2.5–3 cm.
erect on straight pedicels, fusiform, 9–13 × 1–1.2 cm, apex long-acuminate, smooth, pilosulous.
erect on straight pedicels, fusiform, 8–12 × 0.3–0.7 cm, apex long-attenuate, smooth, glabrous.
Asclepias stenophylla
Asclepias cinerea
Although Asclepias stenophylla is a distinctive species, it is difficult to distinguish from A. engelmanniana in the absence of flowers or fruits, where their ranges overlap in the Great Plains. The drooping leaves of A. engelmanniana can reliably distinguish that species from A. stenophylla. Asclepias stenophylla is also often mistaken for A. verticillata, but the nearly appendageless corona segments and alternate or opposite (versus whorled) leaves readily separate A. stenophylla from that species. Because of its slender habit, linear leaves, and small clusters of greenish cream flowers held close to the stem, it can be overlooked in its grassland habitats. Asclepias stenophylla is widespread and common in its core habitat of Ozark glades and dry sites in tallgrass in Missouri, and in mixed-grass prairies from South Dakota to Texas. It is quite rare at the margins of its range in Arkansas (Baxter County), Illinois (Adams, Calhoun, and Pike counties), Iowa (Guthrie, Plymouth, and Sioux counties), Louisiana (Winn Parish), Minnesota (Houston County), Montana (Carter County), and Wyoming (Crook and Weston counties). In Colorado, it exhibits an interesting disjunction between Yuma County in the east and the Front Range of the Rocky Mountains, where it is sporadic, but impacted by development and considered to be of conservation concern. A report from North Dakota has not been confirmed.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Similarities between Asclepias cinerea and A. feayi are discussed under the latter species. Asclepias cinerea inhabits flatwoods mostly north of the range of A. feayi, co-occurring only in Clay County as far as is known. Asclepias cinerea is sympatric with another similar species, A. viridula, across northern Florida. That species tends to grow in wetter woods and meadows than A. cinerea. In flower, they are easily distinguished by the spreading to pendent flowers, ashy lavender corollas, and corona segments with included, crestlike appendages of A. cinerea (versus erect to spreading flowers, green to brownish corollas, and corona segments with exerted, falcate appendages of A. viridula). Asclepias cinerea barely enters southeastern Alabama (Covington, Geneva, and Houston counties), and the species is considered to be of conservation concern in that state. Emergence and flowering of this species appears to be stimulated by precipitation events and/or fire.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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