Subshrubs or shrubs, 60-200 cm (loosely branched, rounded and bushy, ± herbaceous distal to woody bases). Stems erect, simple, slender, wandlike, striate, villous or glabrate, glandular or egland-ular. Leaves present at flowering; sessile; blades linear to oblong or oblanceolate, 8-55 × 1-13 mm, bases cuneate, margins sharply serrate (teeth fine, sharp, bristly), apices obtuse, faces densely villous or adaxial sometimes glabrate or glabrous. Heads (50-100+) in compact paniculiform or corymbiform arrays. Involucres campanulate; staminate 4-6 mm, pistillate 6-8.5 mm. Phyllaries lanceolate, 2-6 mm, margins scarious, medians green (villous), apices acute to acuminate, ciliate, sometimes glandular. Staminate florets 19-26; corollas 4-7 mm. Pistillate florets 20-30; corollas 3.5-5 mm. Cypselae 2.5-3.6 mm, 5-nerved, villous, viscid; pappi 7-8.5 mm.

Baccharis plummerae is recognized by the bushy habit, wandlike, densely villous or glabrate stems, narrowly oblong leaves with sharply serrate margins, and densely villous or glabrate leaves, phyllaries, and cypselae. It is morphologically similar to B. malibuensis.