18. Asclepias cryptoceras S. Watson, Botany (Fortieth Parallel). 283, plate 28, figs. 1–4. 1871.
[E F]
Pallid or jewel milkweed
Herbs. Stems 1–16, prostrate to decumbent, unbranched, 8–25 cm, glabrous, glaucous, rhizomes absent. Leaves opposite, sessile or petiolate, stipular colleters absent; petiole 0–8 mm, glabrous, sometimes with a few long hairs at the base; blade broadly ovate or oval to orbiculate or obovate, 3–7 × 1.8–6 cm, subsucculent, base cuneate or obtuse to cordate or truncate, margins entire, apex rounded to obtuse or acute, mucronate, venation eucamptodromous to faintly brochidodromous, surfaces glabrous, sometimes sparsely strigose on midvein abaxially, glaucous, margins ciliate, laminar colleters absent. Inflorescences terminal, and usually extra-axillary at uppermost node, sessile, 3–10-flowered, with 1 caducous bract at the base of each pedicel. Pedicels 16–35 mm, glabrous. Flowers ascending to pendent, calyx lobes linear-lanceolate, 5–8 mm, apex acute, sparsely strigose to pilosulous; corolla pale green to yellowish green, tinged red abaxially, lobes reflexed with spreading to ascending tips, oval, 8–14 mm, apex acute, glabrous abaxially, papillose at base and minutely hirtellous at tips adaxially; gynostegium sessile; fused anthers dark brown, sometimes green at apex, broadly cylindric, 1.8–3 mm, wings right-triangular with rounded apex, closed, apical appendages deltoid; corona segments red-violet to pinkish purple, sessile, conduplicate, dorsally rounded, 5–8 mm, slightly exceeded by to exceeding style apex, base subsaccate, margins connivent, apex truncate, oblique, with recurved, papillose teeth, papillose, internal appendage absent; style apex slightly depressed, pale green. Follicles sometimes paired, erect on upcurved pedicels, ovoid, 4.5–6 × 1.5–1.8 cm, apex apiculate, smooth, sometimes obscurely ribbed, glabrous, glaucous. Seeds ovate, 8–9 × 6–7 mm, margin very narrowly winged, faces rugulose; coma 2–2.5 cm.
Subspecies 2 (2 in flora): w United States.
Asclepias cryptoceras is one of the most striking milkweeds, with oversized flowers for its small stature. It is widely distributed in the western United States, but it is common nowhere, and occurrences are sporadic. The populations of this species fall into two morphologically discrete entities—those in Arizona, Colorado, southeastern Nevada, Utah, and Wyoming, and those in Idaho, Oregon, and Washington. Plants with intermediate flowers (corona shape and size) are found in eastern California and much of Nevada. The intermediate populations were shown by K. Weitemier (2016) to be genetically similar to subsp. davisii and are treated as such here. Bumblebees (Bombus spp.) have been observed to be avid visitors to the flowers of A. cryptoceras.
