Asclepias stenophylla
Asclepias californica
narrow-leaf milkweed, slimleaf milkweed
California milkweed, round-hood milkweed
1 or 2 (rarely more), erect to spreading, rarely branched, 15–85 cm, puberulent with curved trichomes, not glaucous, rhizomes absent.
1–20+, decumbent to erect, rarely branched, 15–90 cm, densely tomentose, 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 or petiolate, stipular colleters absent;
petiole 0–17 mm, densely tomentose;
blade ovate to lanceolate or oval, 5–18 × 2.5–10.5 cm, chartaceous, base cordate to truncate, margins often minutely erose, apex acuminate, venation eucamptodromous to faintly brochidodromous, surfaces densely tomentose to glabrate, 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, sometimes branched, and extra-axillary at upper nodes, sessile or pedunculate, 5–21-flowered;
peduncle 0–2.5 cm, densely tomentose, with 1 caducous bract at the base of each pedicel.
5–12 mm, puberulent with curved trichomes to pilosulous.
15–40 mm, densely tomentose.
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 linear to narrowly lanceolate, 4–6 mm, apex acute, densely tomentose;
corolla green or tan (sometimes tinged pink) to pinkish purple, red-violet at base, lobes reflexed with spreading tips, oval, 8–11 mm, apex acute, densely tomentose abaxially, pilose at base adaxially;
gynostegial column 2–3.5 mm;
fused anthers dark brown, columnar, 2–2.5 mm, wings right-triangular, closed, apical appendages deltoid;
corona segments red-violet, sometimes pale at apex, sessile, conduplicate, dorsally rounded, 3–6 mm, exceeded by style apex, base slightly to strongly saccate, margins connivent, apex rounded to truncate, slightly to strongly oblique, papillose, internal appendage absent;
style apex planar, green.
ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose;
coma 2.5–3 cm.
broadly oval to orbiculate, 9–12 × 8–11 mm, margin very narrowly winged, faces rugulose;
coma 1.5–2.5 cm.
erect on straight pedicels, fusiform, 9–13 × 1–1.2 cm, apex long-acuminate, smooth, pilosulous.
sometimes paired, erect on upcurved pedicels, ovoid, 5–12.5 × 2–3 cm, apex apiculate to acuminate, longitudinally ridged, densely tomentose.
Asclepias stenophylla
Asclepias californica
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.)
Subspecies 2 (2 in the flora).
Asclepias californica is one of the showiest milkweed species in the flora, with red-violet flowers set off by the dense, white, wooly vestiture of the rest of the plant. It is available from California nurseries but can be difficult to maintain in cultivation. An old report of the species from Baja California Sur cannot be confirmed and likely stems from a misidentification or erroneous location. Although the coronas are notoriously variable within the recognized subspecies, the key characters reliably distinguish northern and southern population systems. However, intermediates can be found in the contact zone, in Kern County.
Gomphocarpus tomentosus (Torrey) A. Gray (not Burchell 1822) is an illegitimate name found in some older regional floras that pertains here.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Corona segments 4–6 mm, apex usually rounded, opening extending from apex to base more than halfway, often more than three-quarters. | subsp. californica |
1. Corona segments 3–4 mm, apex truncate or rounded, opening extending from apex to base less than, rarely up to, halfway. | subsp. greenei |
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