3. Pennellia tricornuta (Rollins) R. A. Price, C. D. Bailey & Al-Shehbaz, Novon. 11: 339. 2001.
Arabis tricornuta Rollins, J. Wash. Acad. Sci. 29: 478. 1939
Stems simple or few from base, 1.5-9 dm, pubescent proximally, trichomes simple and long-stalked, 2-3-rayed. Basal leaves usually persistent; petiole 0.5-3 cm; blade oblanceolate, 3-9 cm × 3-23 mm, margins dentate, surfaces pubescent, trichomes stalked, 2-4-rayed. Cauline leaves (distal) sessile; blade linear, 2.7-7.5 cm × 1-9 mm, surfaces glabrous or sparsely pubescent. Racemes secund, 2-6 dm in fruit. Fruiting pedicels ascending, arcuate, 7-11 mm. Flowers: sepals purple or green, oblong, 2.3-4 × 0.8-2.1 mm, (subequal); petals lavender apically, spatulate, (2.7-)3.3-4.5 × (0.5-) 1-1.5(-1.7) mm, (equal); filaments (1.7-)2-2.8(-3.3) mm; anthers 0.9-1(-1.3) mm. Fruits divaricate-ascending, straight or curved, 3.3-6.5 cm × 2-2.5 mm, latiseptate; valves glabrous; septum opaque; ovules 40-50 per ovary; style obsolete to 0.2 mm. Seeds uniseriate, flattened, winged, oblong, 2.4-2.8 × 1.2-1.9 mm; seed coat not mucilaginous when wetted; cotyledons accumbent.
Flowering Jul-Sep. Steep rocky slopes, under pines, road and sand banks; of conservation concern; 1300-2800 m; Ariz.
Pennellia tricornuta is known from Cochise, Pima, and Santa Cruz counties. It was recognized by R. C. Rollins (1941, 1993) under Arabis, but as shown by Price, Bailey & Al-Shehbaz and by S. Fuentes-Soriano (2004), it clearly belongs to Pennellia.