84. Eriogonum arborescens Greene, Bull. Calif. Acad. Sci. 1: 11. 1884.
Santa Cruz Island wild buckwheat
Shrubs, erect to spreading, 6-15(-20) × 5-30 dm, glabrous and cinereous, reddish. Stems spread-ing to erect, occasionally with persistent leaf bases, up to 3/4 or more height of plant; caudex stems absent; aerial flowering stems erect, stout, solid, not fistulose, 0.5-1(-1.5) dm, glabrous. Leaves cauline, 1 per node; petiole 0.1-0.5 cm, tomentose; blade linear to narrowly oblong, 2-4(-5) × 0.1-0.4(-0.6) cm, white-tomentose abaxially, cinereous to glabrate and greenish adaxially, margins often revolute. Inflorescences cymose, 5-10 × 5-15(-20) cm; branches dichotomous, glabrous; bracts 1-3, leaflike, lanceolate to oblong, 0.5-2 × 0.3-1.5 cm. Peduncles absent or erect, stout, 0.1-0.5 cm, cinereous. Involucres 1 per node, campanulate, 2-3 × 2.5-4 mm, cinereous; teeth 5-7, erect, 0.5-1.5 mm. Flowers 2-3.5(-4) mm; perianth white to pinkish, villous abaxially; tepals connate proximally, monomorphic, oblanceolate to narrowly obovate; stamens exserted, 3-5 mm; filaments glabrous. Achenes brown, 2.5-3.5 mm, glabrous. 2n = 40.
Flowering Apr-Oct. Rocky slopes and canyon walls, coastal scrub communities; of conservation concern; 10-600 m; Calif.
Eriogonum arborescens is local and occasionally rare on Santa Cruz, Santa Rosa, and Anacapa islands in Santa Cruz and Ventura counties. The species is cultivated, and populations have become naturalized on the mainland from San Mateo County south to San Diego, in large part because of planting along highways. Every effort should be made to remove these naturalized populations from the mainland.