Asclepias macrotis

Illustrator: Barbara Alongi

Copyright: Flora of North America Association

Subshrubs, densely cespitose. Stems few–numerous, erect to ascending, branched at base, 10–35 cm, minutely puberulent with curved trichomes in a line to glabrate, not glaucous, rhizo­matous. Leaves opposite, ses­sile, with 1 stipular colleter on each side of leaf base; blade fili­form, 2.5–7 × 0.05–0.15 cm, membranous, base cune­ate, margins revolute, apex acute, mucronate, vena­tion obscure, surfaces glabrous, margins minutely ciliate at base, laminar colleters absent. Inflorescences extra-axillary, sessile or pedunculate, 2–7-flowered; peduncle 0–0.8 cm, puberulent with curved trichomes, with 1 caducous bract at the base of each pedicel. Pedicels 6–10 mm, minutely puberulent with curved trichomes in a line. Flowers erect; calyx lobes lanceolate, 2–2.5 mm, apex acute, glabrous; corolla greenish cream tinged with red, lobes reflexed with spreading tips, oval, 4–5 mm, apex acute, glabrous; gynostegial column 0.5–1 mm; fused anthers brown, cylindric, 1–1.5 mm, wings right-triangular, closed, apical appendages broadly ovate; corona segments cream to greenish cream, reddish brown at base or as a dorsal stripe, subsessile, con­duplicate, 4–5 mm, exceeding style apex, apex truncate, long-caudate, crisped, with a proximal tooth on each side, hirtellous, internal appendage falcate, exserted, inflexed towards style apex, hirtellous; style apex shallowly depressed, green. Follicles erect on upcurved pedicels, fusiform, 4.5–6 × 0.5–0.7 cm, apex attenuate, smooth, glabrous. Seeds ovate, 6–8 × 2.5–4 mm, margin thickly winged, faces rugulose; coma 2–2.5 cm.

Phenology: Flowering May–Oct; fruiting Jun–Oct.
Habitat: Mesas, hills, slopes, flats, canyon rims and bottoms, arroyo margins, limestone, sandstone, shale, rhyolite, gypsum, caliche, cracks in bedrock, talus, gravel and sandy soils, oak, pine-oak, juniper, and pinyon-juniper woodlands, chap­arral, shrubby grasslands, desert grasslands, prairies.
Elevation: 1100–2200 m.

Distribution

• Generated Map
• Legacy Map

Ariz., Colo., N.Mex., Okla., Tex., Mexico (Chihuahua, Coahuila, Sonora).

Discussion

With a suffruticose, cespitose, intricately branched habit, the only other milkweed with which Asclepias macrotis can be confused is the rarely encountered A. sperryi, which is restricted to the Big Bend region of Texas in the flora area. Although A. macrotis ranges across western Texas, it appears to be absent from Big Bend; no mixed populations of these species are known, and hybridization is neither known nor suspected. Its distribution in Colorado is limited to the southeastern corner of the state and in Oklahoma to the extreme tip of the Panhandle, in Cimarron County. In Arizona, it is more common but limited to the three southeastern counties: Cochise, Pima, and Santa Cruz. The elongate, curled apices of the corona segments are unique, and the small, drab flowers are quite elegant.

Selected References

None.

Lower Taxa

None.