Herbs 2–30 cm. Leaves: petiole 1–2 cm; blade narrowly lance­olate to ovate, 3.5–9 × 1–5 cm, base rounded to truncate or shallowly cordate, margins cili­ate, apex acute to obtuse, sur­faces more densely eglandular-hairy on veins and margins, glandular hairs restricted to veins and margins, laminar colleters 6–12. Inflores­cences 3–10-flowered; peduncle 0–7 mm. Pedicels 0.5–1 cm. Flowers: calyx lobes slightly recurved, lanceolate, 3–4 mm; corolla scarcely reticulate distally at margins, tube 1.5–2 mm, glabrous, lobes narrowly lanceolate, 3–4 mm, abaxially sparsely to moderately villous, adax­ially densely villous; corona segments much shorter than style apex, apex truncate with 2 marginal teeth; apical anther appendages lanceolate; style apex elongate, yel­low, domelike, 1–1.5 mm, shallowly 2-lobed. Follicles unknown.

Flowering Jul–Sep. Terrace of wide canyon bottom at base of mountains, pine-oak-juniper woodlands; 1700 m; Ariz.; c, n Mexico.

Pherotrichis schaffneri is known in the flora area only from the southern Huachuca Mountains in Cochise County. It had been documented by a single 1882 collection (Lemmon 2816), and the existence of P. schaffneri in the United States was questioned until it was rediscovered by J. Ksepka in 2015 (Ksepka s.n. [OKLA]), 133 years later. The site is an unremarkable patch of open woodland on a lower canyon slope, sur­rounded by thousands of acres of seemingly suitable habitat. Despite the apparent rarity of P. schaffneri in Arizona, it has not been afforded conservation status, in part because Lemmon’s locality in the United States was unconfirmed and also because of unresolved taxonomic questions (see below). Although P. schaffneri is not uncommon in the northern Sierra Madre Occidental in Mexico, it is exceedingly rare in the United States, where conservation status seems warranted.

The Lemmon collection from the Huachuca Mountains served as a syntype for Pherotrichis schaffneri; however, this name was lectotypified by another syntype (Schaffner 63, lectotype GH) from San Luis Potosí, Mexico (W. D. Stevens 2005). The names Matelea balbisii (A. Gray) Woodson and P. balbisii A. Gray are most commonly applied to P. schaffneri throughout its range but are illegitimate as they are based on Asclepias villosa Balbis, a later homonym of A. villosa Miller, as shown by Stevens. It is questionable whether the population in Arizona and morphologically similar populations in Chihuahua, Durango, and Sonora, Mexico, are conspecific with the populations in San Luis Potosí represented by the type of P. schaffneri. Additional work building on the revisionary study by L. Lozado Pérez (2003) will be required to resolve this question.