Asclepias hypoleuca

Herbs. Stems 1 (rarely 2 or 3), erect, unbranched, 25–100 cm, puberulent with curved tri­chomes to pilosulous, not glau­cous, rhizomes absent. Leaves opposite, petiolate, with 1 stip­ular colleter on each side of petiole; petiole 2–6 mm, puberulent with curved trichomes to pilosulous; blade ovate or lanceolate to oblong, elliptic, or oval, 5.5–11.5 × 1–5 cm, chartaceous, base cuneate or obtuse to trun­cate, margins entire, apex obtuse to rounded, mucro­nate, venation eucamptodromous, sur­faces tomentose abaxially, pilosulous or tomentulose to glabrate adax­ially, margins ciliate, 8–12 laminar colleters. Inflorescences terminal and extra-axillary, pedunculate, 12–35-flowered; peduncle 3.5–10.5 cm, puberulent with curved trichomes to tomentulose, with 1 caducous bract at the base of each pedicel. Pedicels 15–21 mm, densely puberulent with curved trichomes or pilosulous to tomentulose. Flowers erect to pendent; calyx lobes lanceolate, 3–4 mm, apex acute, pilose; corolla green, sometimes red-tinged abaxially, deep maroon to greenish red or green adaxially, lobes reflexed, tips usually spreading, oblong to elliptic, 8–10 mm, apex acute, pilosulous abaxially, glabrous adaxially; gynostegial column 1–1.5 mm; fused anthers brown, broadly cylindric, 2–2.5 mm, wings right-triangular, open at tip, apical appendages ovate, erose; corona segments deep maroon to greenish red or yellowish green, subsessile, conduplicate, 7–9 mm, greatly exceeding style apex, apex truncate, spreading and long-tapering with a proximal tooth on each side, glabrous, internal appendage absent or a low crest, glabrous; style apex shallowly depressed, green. Follicles erect on upcurved pedicels, fusiform, 9–11.5 × 1.2–1.4 cm, apex long-attenuate, smooth, sometimes faintly striate, pilosulous to tomentulose. Seeds ovate, 6–7 × 4–5 mm, margin winged, faces minutely rugulose; coma 3–3.5 cm.

Phenology: Flowering Jun–Sep; fruiting Aug–Sep.
Habitat: Slopes, flats, lake shores, streamsides, granite, gneiss, andesite, rocky soils, pine, pine-oak, oak, and mixed-conifer forests.
Elevation: 1900–2800 m.

Distribution

• Generated Map
• Legacy Map

Ariz., N.Mex., Mexico (Chihuahua, Sonora).

Discussion

Asclepias hypoleuca grows at higher elevations in the sky-island mountain ranges than any other milkweed. It has been documented from the Chiricahua, Huachuca, Rincon, Santa Catalina, Santa Rita, and White moun­tain ranges in Arizona (Cochise, Pima, and Santa Cruz counties) and the Mogollon Mountains and Black Range in New Mexico (Catron and Grant counties). Because of its limited, high-elevation distribution, and the threats of changing climate, its conservation status in the flora area merits assessment. The bicolored leaves exhibit coloration similar to co-occurring silverleaf oak (Quercus hypoleucoides).

Selected References

None.

Lower Taxa

None.