As noted by Panero (2007), Perymenium Schrad. is a rather large genus with 50 or more species, most of them located in Mexico, these last treated by Turner (2014), in which five species were recorded for the state of Sonora, or along its boundaries.

Perennial herbs to 1 m high (roots not examined). Mid-stems pubescent with upwardly appressed minute hairs. Leaves ovate-lanceolate, opposite throughout, mostly 6-10 cm long, 1.5-2.5 cm wide, pubescent like the stems, 3-nervate from near the base, their margins entire or nearly so; petioles 5-10 mm long. Capitulescence a terminal array of 10-30 heads, 4-8 cm across. Heads ca. 8 mm high, 4 mm wide, their ultimate peduncles 1-3 cm long. Involucral bracts broadly ovate, 3-4 seriate, rounded to obtuse at apex, the upper margins sparsely ciliate. Receptacle convex. Pales linear, 4-7 mm long. Ray florets, 8-11, pistillate, fertile; ligules yellow, 6-8 mm long, 1-2 mm wide. Disc florets, 15-20 per head; corollas yellow, glabrous, 4-5 mm long; tubes ca. 1.5 mm long; throats ca. 3 mm long; lobes ca. 0.5 mm long. Achenes of ray and disc florets similar, 2-sided, bearing a pappus of short, readily deciduous, bristles 1-3 mm long.

Type: MEXICO. Sonora: Mpio. Bacanora, Restaurant el Torreoncito, 11.8 km (by air) WSW of Bacanora, 28°56′59″N, 109°31′01″W, 949 m. “Foothills thorn scrub. Common herbaceous perennial on roadside,” 30 Jul 2014, T.R. Van Devender et al. 2014-365 (Holotype: TEX). Fig. 1.

Fig. 1. 

The type specimen of Perymenium vandevenderorum B.L. Turner located at TEX.

Additional specimens examined: MEXICO. Sonora: Las Tierras de Jimenez, Sierra de Murrieta, 28°33′33″N, 109°31′33″W, “Open woodland on limestone ridge. Occasional herbaceous perennial” 1 Aug 2014, T.R. Van Devender et al. 2014-331 (TEX).

This novelty is readily recognized by its robust habit and entire leaves, the latter strikingly different from closely related taxa, namely Perymenium nesomii B.L. Turner of nearby southwestern Chihuahua that appears to be its nearest relative; indeed, it will key to, or near, that species in my treatment of the genus for Mexico, the taxon endemic to the Cascada de Basaseachic of SW Chihuahua. Perymenium vandevenderorum is readily identified by its larger, more branched habit, entire leaves (vs. serrate) and somewhat larger heads. Distribution of the two species is shown in Fig. 2.

Fig. 2. 

Distribution of Perymenium vandevenderorum and P. nesomii in Mexico.

The collectors of the plants concerned describe the material as perennial herbs, but they appear to be more nearly like sub-shrubs, only the upper parts of the collections mounted, as noted above and shown on the type itself.

It's a pleasure to name the novelty for my close friend, Thomas R. van Devender and his wife Ana Lila Reina, who collected both of the above cited specimens.