Asclepias stenophylla
Asclepias lanuginosa
narrow-leaf milkweed, slimleaf milkweed
asclépiade laineuse, side-cluster milkweed, small-green milkweed, woolly milkweed
1 or 2 (rarely more), erect to spreading, rarely branched, 15–85 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
1 or 2 (rarely more), erect to spreading, unbranched, 7–20 cm, densely hirtellous to pilose, not glaucous, rhizomatous.
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 or alternate, petiolate, with 1 stipular colleter on each side of petiole;
petiole 1–2 mm, hirtellous;
blade oblong or lanceolate to narrowly lanceolate, 4–8 × 0.5–2.7 cm, chartaceous, base cuneate to rounded or subcordate, margins entire, apex acute to obtuse, venation eucamptodromous to reticulodromous, surfaces hirtellous, margins ciliate, 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, usually solitary, pedunculate, 17–50-flowered (rarely more);
peduncle 1–3 cm, densely hirtellous to pilose, with 1 caducous bract at the base of each pedicel.
5–12 mm, puberulent with curved trichomes to pilosulous.
9–13 mm, hirtellous to pilose.
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.
erect to spreading;
calyx lobes narrowly lanceolate, 1.5–2 mm, apex acute, hirtellous;
corolla greenish cream, sometimes purple-tinged, lobes reflexed, oblong, 3–5 mm, apex acute, glabrous;
gynostegial column 0–0.2 mm;
fused anthers green, broadly cylindric, 1.5–2 mm, wings triangular, widest below middle, closed, apical appendages ovate;
corona segments cream to greenish cream, sessile, chute-shaped, margins incurved, appressed to column, 2–3.5 mm, exceeded by style apex, base saccate, apex rounded, glabrous, internal appendage absent or obscure, glabrous;
style apex shallowly depressed, green to greenish cream.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
ovate, 6–7 × 4–5 mm, faces minutely rugulose;
comose.
erect on straight pedicels, fusiform, 9–13 × 1–1.2 cm, apex long-acuminate, smooth, pilosulous.
erect on upcurved pedicels, fusiform, 8–10 × 0.8–1.5 cm, apex long-acuminate, smooth, hirtellous to pilose.
= 22.
Asclepias stenophylla
Asclepias lanuginosa
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.)
Asclepias lanuginosa is highly cryptic due to its small stature and early flowering. It resembles a short, hirtellous form of A. viridiflora. In addition to the differences in vestiture, A. lanuginosa can be distinguished from that species by the terminal inflorescence and the cream-colored corona segments. Due to severe habitat loss in the tallgrass prairie region, A. lanuginosa has apparently declined and is of conservation concern over much of its range, that is, in Illinois, Iowa, Kansas, North Dakota, South Dakota, and Wisconsin. It is more secure in Nebraska, but an overall re-assessment of the status of this species is warranted. The only report from Montana is from the “Yellowstone expedition,” which may not have been collected in the state. R. E. Woodson Jr. (1954) considered A. lanuginosa Kunth (a later homonym) to be the correct name for a Mexican species, A. otarioides E. Fournier. He soon realized that A. lanuginosa Nuttall has priority, but prior usage and his extensive annotations produced lingering confusion over the correct name of the Mexican species. Torrey’s replacement name for this species, A. nuttalliana, is illegitimate, as it was superfluous on publication.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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