Shrubs, 50-200 cm (freely branched, broomlike) . Stems erect, fastigiate, striate-angular, green, glabrous, resinous. Leaves cauline (proximal withering and sparse by flowering); sessile; blades (1-nerved) broadly oblanceolate to obovate or spatulate, 10-35 × 5-15 mm (thick, firm), bases attenuate , margins entire or irregularly serrate (teeth 1-4, distal leaves entire), apices obtuse to acute, faces glabrous, gland-dotted, resinous. Heads (sessile or short-pedunculate on lateral branches) in crowded paniculiform arrays. Involucres funnelform to campanulate; staminate 3-5 mm, pistillate 3-5 mm. Phyllaries ovate to linear-lanceolate, 1-5 mm, margins scarious, erose, medians green, apices rounded to acute, glabrous, gland-dotted, resinous. Staminate florets 24-33; corollas 2-3.5 mm. Pistillate florets 15-30; corollas 1.6-2.7 mm. Cypselae 1-2 mm, prominently 10-nerved, glabrous; pappi 1.7-3.1 mm. 2n = 18. Flowering Jul-Oct. Gravelly or sandy streambeds, dry washes, grasslands; 100-1800 m; Ariz., Calif., Nev., Utah; Mexico (Baja California, Sonora). Baccharis sergiloides is recognized by its fastigiate, broomlike habit, and large obovate leaves that often wither before flowering. It differs from B. sarothroides in its larger leaves, more or less sessile and lateral heads, and smaller florets and fruits.

Plant: Shrub < 2 m, glabrous, generally sticky; stems: branches generally many, erect, often leafless at flower Leaves: cauline, alternate, simple, barely petioled, < 35 mm, oblanceolate to obovate, 0-4-toothed; principal vein 1 INFLORESCENCE: primary inflorescence a head, each resembling a flower; heads in a panicle; involucre funnel- to bell-shaped, of staminate heads 2.2-4 mm, of pistillate heads 3-4.5 mm; phyllaries in 4-6 series, lanceolate, hard, glabrous, generally sticky, tip rounded to acute; receptacle conic to convex, generally smooth, glabrous to puberulent, chaff sometimes 0 in staminate plants Flowers: Staminate flowers (11)24-33; corollas 2.2-3.3 mm, white to pink-tinged; ovary much reduced; pappus 2-3 mm, of bristles < involucre; Pistillate flowers 15-30; corollas 1.6-2.7 mm, thread-like, ± whitish Fruit: achenes, cylindric, 1-1.5 mm, glabrous; ribs 10; pappus 1.7-3.1 mm, of many bristles > involucre Misc: Gravelly or sandy streambeds; 600-1575 m.; May-Oct