Brickellia sect. Xerobrickellia Robinson (1917: 31)

Schilling, Edward E., Scott, Randall W. & Panero, Jose L., 2015, A revised infrageneric classification for Brickellia (Asteraceae, Eupatorieae), Phytotaxa 234 (2), pp. 151-158 : 157

9. Brickellia sect. Xerobrickellia Robinson (1917: 31) . Lectotype (here chosen):— Brickellia longifolia S. Watson.

Species:— Brickellia baccharidea A. Gray ; B. brandegeei B.L. Rob. ; B. californica A. Gray ; B. cardiophylla B.L. Rob. ; B. dentata Sch.Bip. ; B. desertorum Coville ; B. floribunda A. Gray ; B. knappiana* Drew ; B. laciniata A. Gray ; B. longifolia S. Watson ; B. multiflora* Kellogg ; B. rhomboidea Greene ; B. rusbyi A. Gray.

Geographic distribution:—Primarily in the Sierra Madre Oriental, northern Sonoran Desert, or on the Colorado Plateau or, if more widespread, in some combination of these areas. The basally diverging species of the section, B. cardiophylla is exceptional in occurring in the Trans-Volcanic Belt region (Nayarit-Jalisco states). Many of the species are principally mid-elevation (1100–2600 m) montane in distribution, although B. rhomboidea (1–100m) and B. brandegeei (100–300 m) are near sea-level endemics; B. baccharidea (500–1600 m) bridges into the Lower Sonoran region in a few localities and B. californica drops into the Sonoran Desert region across its widespread distribution.

Phenology:—Predominantly fall flowering, but B. cardiophylla is again exceptional, flowering March–May.

Habitat:—Mostly rocky desert hillsides, or pine-oak forest ( B. floribunda , B. rusbyi ).

Endemism:—Six species are narrow endemics ( B. cardiophylla , B. rhomboidea , B. brandegeei , B. dentata , B. longifolia , B. desertorum ); four have somewhat expanded distributions (regional endemics: B. rusbyi , B. floribunda , B. laciniata , B. baccharidea ) whereas only B. californica can be considered widespread.

Morphological trends:—The leaves are petiolate, but the species of drier and lower elevations have shorter petioles. The leaves ovate-rhomboid, becoming narrower and smaller in species of drier and lower regions; larger leaves have the first pair of lateral veins diverging from the midrib above the leaf margin. Flower number per head is 50–60 in B. cardiophylla and B. rhomboidea and 28–30 in B. brandegeei , but fewer (13–ca. 25) in most other species (3–7 in B. longifolia ; 8–12 in B. desertorum ) that are often found in somewhat lower and drier habitats. Pendulous heads arose twice: once in the common ancestor of B. rusbyi and B. floribunda and, again, in B. baccharidea and B. californica .

Taxonomic issues:—The widespread and variable B. californica and its relationship with B. desertorum remain in need of study.