Serpentine milkweed

Gomphocarpus purpurascens A. Gray, Proc. Amer. Acad. Arts 10: 76. 1874, not A. Richard 1850; Solanoa purpurascens Greene 1890, not Asclepias purpurascens Linnaeus 1753

Herbs. Stems 1–15, prostrate, unbranched (rarely branched), 15–40 cm, densely puberulent with curved trichomes to tomentose, not glaucous, rhizomes absent. Leaves opposite, petiolate, stipular colleters absent; petiole 5–10 mm, densely puberulent with curved trichomes; blade ovate to nearly orbiculate, 3.5–6 × 3–4 cm, subsucculent, base obtuse to cordate, margins entire, apex obtuse to acute or rounded, venation eucamptodromous, surfaces pilosulous, more densely so abaxially, especially on veins, becoming glabrate adaxially, margins inconspicuously ciliate, laminar colleters absent. Inflorescences terminal and extra-axillary, pedunculate, 20–55-flowered; peduncle 1.5–9 cm, tomentose, with 1 caducous bract at the base of each pedicel. Pedicels 10–13 mm, tomentose to pilose. Flowers erect to spreading; calyx lobes lanceolate, 2–3 mm, apex acute, pilose to tomentose; corolla pale pink to red, lobes reflexed with spreading tips, oval, 5–6 mm, apex acute, glabrous; gynostegium sessile; fused anthers yellow to brown or green, broadly barrel-shaped, 1.5–2 mm, wings deltoid, widest at middle, closed, apical appendages ovate; corona segments pinkish cream to cream, subsessile, conduplicate, dorsally rounded, spreading away from anthers, 2–3 mm, greatly exceeded by style apex, apex truncate, glabrous, internal append­age absent; style apex shallowly depressed, cream to green. Follicles erect on upcurved pedicels (at least until maturity), lance-ovoid, 6–10 × 2–3 cm, apex obtuse to acuminate, longitudinally ridged, pilosulose or tomentulose to glabrate. Seeds ovate, 6–8 × 5–6 mm, margin very narrowly winged, faces rugulose; coma 2–2.5 cm.

Flowering (Apr–)May–Aug; fruiting Jun–Jul. Slopes, streamsides, canyons, barrens, serpentine, rocky and deep soils, chaparral, cypress and mixed-conifer woodlands, pine and mixed-conifer forests, meadows; 200–2000 m; Calif.

Asclepias solanoana is a delightful and unique milk­weed that is endemic to rugged, serpentine barrens in the northern Coast Range of California. The plants hug the ground, the stems seeming to crawl outward propelled by the highly unusual metallic, grayish or bluish green, ovate leaves. Bright pinkish rose balls of floral buds are held above, and are followed by variegated spheres of cream, pink, green, and brown flowers with a vague resemblance to heads of Abronia (Nyctaginaceae). It is often the only conspicuous plant species on highly exposed, south-facing slopes. S. P. Lynch (1977) docu­mented Hymenoptera (carpenter bees, Xylocopa, bumblebees, Bombus, and honeybees, Apis) to be the main pollinators of A. solanoana. It is considered threatened by extractive industries and recreation at some sites. A naturally occurring population has been reported from southern Oregon and needs confirmation.

SELECTED REFERENCE Lynch, S. P. 1977. The floral ecology of Asclepias solanoana Woods. Madroño 24: 159–177.