Plant: perennial herb; stems erect, unbranched or with a few lateral shoots from the middle and upper nodes, 20-70 cm tall, finely pubescent in lines above the petioles or becoming glabrous Leaves: opposite, subsessile, the petioles 1-6 mm long, the blades linear to narrowly lanceolate or elliptic, 4-12 cm long, 2-11(-15) mm broad, attenuate at apex and base, glabrous on both surfaces, or with a few hairs on the margins and midvein below INFLORESCENCE: UMBELS lateral in the upper portion of the stem, one per node, or infrequently single and appearing terminal, 2-3 cm broad, the peduncles 1-6 cm long Flowers: small; calyx lobes ca. 2.5 mm long; corolla white or flushed with pale purple, the lobes 5-6 mm long; hoods white, erect-ascending, obovoid-oblong, 2.5-3.4 mm long, 1.6-2.2 mm broad along the sloping apex, about as long as to slightly longer than the gynostegium, obtuse-rounded above, the horns digitate, attached near the base of the hoods, exserted ca. 2 mm and arching over the stigma head; anther wings 1.6-2 mm long; corpusculum ca. 0.2 mm long, the pollinia 1.1-1.2 mm long Fruit: FOLLICLES erect on erect pedicels, 5-9 cm long Misc: Riparian woodlands and canyons, mts; 1050-1750 m (3500-5700 ft); May-Aug REFERENCES: Sundell, Eric. 1994. Asclepiadaceae. J. Ariz. - Nev. Acad. Sci. Volume 27, 169-187.

Sundell 1993, Wiggins 1964, Woodson 1954, Nabhan et al 2015

Duration: Perennial Nativity: Native Lifeform: Forb/Herb General: Slender plants with multiple unbranched, erect stems arising from the fibrous roots, somewhat suffrutescent, 20-70 cm tall, finely pubescent lines above petioles but becoming glabrous. Leaves: Opposite, subsessile, on petioles 1-6 mm long, the blades linearly to narrowly lanceolate to elliptic, these 4-12 cm long, 2-11 mm wide, apex and base narrowing to a point, glabrous above and below, moderately revolute to plane. Flowers: Umbels lateral in upper part of stem at upper nodes, appearing terminal, 2-3 cm across, with peduncles 1-6 cm long, the flowers small with calyx lobes about 2.5 cm long, the corolla white, commonly with a pinkish tinge, the lobes 5-6 mm. Fruits: Erect, slender follicles on pedicels 5-9 cm long. Ecology: Found in riparian woodlands, floodplain meadows, cienega edges, canyons and arroyo bottoms from 3,500-7,000 ft (1067-2286 m), flowers May-August. Distribution: s AZ to s TX, south through Sonora, Chihuahua and mountainous regions throughout MEX to Chiapas. Notes: The narrow leaves are distinctive, can be confused with A. incarnata, but distinguished by the white flowers as opposed to bright purple in the other species, along with the solitary umbel in the upper nodes. Can flower sporadically throughout the year. The species is rare in Arizona and limited to the borderlands there, but said to be very frequent in the Mexican uplands (Woodson 1954). It is known monarch host plant. Ethnobotany: Unknown Etymology: Asclepias is named for the Greek god of healing Asklepios, while angustifolia means narrow leaves. Synonyms: None Editor: SBuckley 2011, 2014, AHazelton 2015