Brickellia sect. Brickellia

Schilling, Edward E., Scott, Randall W. & Panero, Jose L., 2015, A revised infrageneric classification for Brickellia (Asteraceae, Eupatorieae), Phytotaxa 234 (2), pp. 151-158 : 153-155

2. Brickellia sect. Brickellia .

Species:— Brickellia cordifolia Elliott ; B. enigmatica B.L. Turner ; B. grandiflora Nutt. ; B. hastata* Benth. ; B. hymenochlaena A. Gray ; B. jaliscensis McVaugh ; B. magnifica McVaugh ; B. megaphylla M.E. Jones ; B. monocephala B.L. Rob. ; B. nutanticeps S.F. Blake ; B. odontophylla A. Gray ; B. robinsoniana* S.F. Blake ; B. simplex A. Gray ; B. stolonifera* B.L. Turner ; B. urolepis S.F. Blake.

Geographic distribution:—Mostly Sonora, Chihuahua and Coahuila and radiating out from this center to Baja California Sur ( B. megaphylla ), down into the Central Plateau (Durango, Zacatecas) and into the Trans Volcanic Region (Jalisco, Michoacan, Mexico), B. hymenochlaena extends down the east coast (Hidalgo, Puebla) back into Oaxaca whereas B. monocephala extends west along the coast into Guerrero and southern Oaxaca; B. cordifolia is disjunct in eastern U.S. Mostly at mid to high elevation 1600–2500 m (– 3500 m, B. nutanticeps ), except B. megaphylla and two species that extend into the U.S. ( B. cordifolia , B. grandiflora ).

Phenology:—Late summer–fall (Aug–Oct) except for B. magnifica (March–April).

Habitat:—Pine-oak forest except for B. megaphylla (rocky hillsides and canyons of southern Baja California).

Endemism:—Seven rather narrow endemics; four regional endemics ( B. hymenochlaena, Sierra Madre Oriental : eastern Nuevo Leon, Tamaulipas, eastern San Luis Potosi, Hidalgo, Puebla, Veracruz and eastern Oaxaca; B. monocephala , Central Plateau and adjoining highlands:, western Durango, Zacatecas, Jalisco, Michoacan, Mexico, and e. Hidalgo; B. nutanticeps, Trans Volcanic Region, Michoacan, Mexico, Morelos, Guerrero, Oaxaca; and B. simplex , northeastern Sonora, Chihuahua, Coahuila, and southern Arizona), & one widespread ( B. grandiflora ).

Morphological trends:—Perennial herbs or subshrubs; leaves mostly opposite, mostly ovate, cordate to truncate, larger leaves with naked basal veins, the lateral veins marginal at the point of divergence from the base of the midrib, mostly petiolate; heads nodding (except for B. cordifolia and B. jaliscensis ; these two species are also the exceptions to the correlation of species from pine-oak forests having nodding heads); heads with numerous flowers, 25+, except for B. jaliscensis 10–20.

Taxonomic issues:—The species of this section appear to be well delimited based on morphology and distribution. Curious are the close affinities between B. megaphylla and B. hymenochlaena which both have closely packed corymbs; B. odontophylla and B. simplex which are quite similar and distinguished by the number of heads and their leaf margins; B. odontophylla with its nodding, secund heads and alternate, long-petiolate, subcordate leaves bears a striking similarity to elements of B. secundiflora .

3. Brickellia sect. Coleosanthus (Cass.) E.E. Schill. & R. Scott. , stat. nov. Coleosanthus Cassini (1817: 67). Type:— Brickellia cavanillesii (Cass.) A. Gray

Species:— Brickellia amplexicaulis B.L. Rob. ; B. aramberrana B.L. Turner ; B. argyrolepis B.L. Rob. ; B. atarjea* B.L. Turner ; B. betonicifolia A. Gray ; B. brachyphylla (A. Gray) A. Gray ; B. cavanillesii (Cass.) A. Gray ; B. cuspidata A. Gray ; B. cylindracea A. Gray & Engelm. ; B. gentryi* B.L. Turner ; B. glandulosa (La Llave) McVaugh ; B. glomerata Fernald ; B. hinckleyi Standley ; B. lanata A. Gray ; B. lemmonii A. Gray ; B. lewisii B.L. Turner ; B. oligadenia (B.L. Rob.) B.L. Turner ; B. oliganthes A. Gray ; B. orizabensis Klatt ; B. palmeri A. Gray ; B. paniculata B.L. Rob. ; B. parvula A. Gray ; B. pendula A. Gray ; B. peninsularis Brandegee ; B. pringlei A. Gray ; B. secundiflora A. Gray ; B. seemannii* A. Gray ; B. serboana* B.L. Turner ; B. squarrosa* B.L. Rob. & Seaton ; B. tomentella A. Gray ; B. venosa B.L. Rob. ; B. wendtii B.L. Turner ; B. wislizeni A. Gray ; B. worthingtonii B.L. Turner.

Brickellia sect. Coleosanthus is the largest section of the genus, and includes three major clades which we denote here as the B. secundiflora clade, the B. lewisii clade, and the B. wendtii clade (named for the first diverging taxon in each lineage from the molecular phylogenetic tree; Schilling et al. 2015).

Geographic distribution:—The B. secundiflora clade is rooted in three other widespread species besides B. secundiflora ; B. argyrolepis (Chiapas and south), B. oliganthes (Sierra Madre Occidental, Trans Volcanic Belt and Sierra Madre Sur) , and B. paniculata (from Tamaulipas across to Sinaloa and south along the Sierra Madre Occidental, across much of the Trans Volcanic Belt, and south through Oaxaca and Chiapas to Guatemala). Other somewhat widespread species include B. cavanillesii , B. tomentella , and B. pendula which have distributions centered in the Trans Volcanic Belt and Sierra Madre Sur and are interspersed with the endemic species B. aramberrana (Nuevo Leon), B. palmeri (San Luis Potosi) and B. orizabensis (Veracruz, northern Oaxaca, and Guerrero). The B. lewisii clade is composed primarily of narrow endemics or species with limited distributions. Only the morphologically and genetically variable species, B. lemmonii , has any breadth to its distribution. Brickellia lewisii (Basaseachi, Chihuahua), B. worthingtonii (Durango), B. wislizeni (Chihuahua, northern Durango) and B. cylindracea (central Texas) are endemics. This clade’s center appears to be in northern Sierra Madre Occidental (Chihuahua, Durango, Sonora) and to be primarily confined to pine-oak habitats except for B. peninsularis which occurs in the lowlands of Baja California Sur and B. cylindracea which is found in riparian habitats of central Texas. The B. wendtii clade appears to have radiated from north-eastern Mexico (Coahuila) west into Sonora, Chihuahua, the adjoining U.S., across to northern Baja California ( B. betonicifolia , B. pringlei ) south into Durango, Jalisco, and Colima ( B. lanata ; B. cuspidata endemic to Jalisco). Several species have radiated into the tropical deciduous forests along both coasts: B. glandulosa (widespread from central-eastern Mexico to Nicaragua), B. glomerata (western Trans Volcanic Belt to the Pacific Slopes of Michoacan, Guerrero, and Oaxaca), B. oliganthes (Nayarit and Jalisco to Veracruz), and B. oligadenia (Jalisco to Guerrero). Three species, B. lemmonii , B. brachyphylla , and B. parvula make up a subclade with distributions extending from eastern Arizona to western Texas. Most species of B. sect. Coleosanthus can be found in mid elevations between 1000–2000 m with some extending to 2500 m; exceptions include B. peninsularis which occurs from sea level to 300 m in southern Baja California Sur, and the widespread B. oliganthes which occurs from sea level to 1500 m.

Phenology:—The majority of species flower in fall to winter, Aug–Jan, but B. oligadenia flowers Jan–May while B. oliganthes appears to flower in all seasons.

Habitat:—Pine-oak and tropical deciduous forests to desert grasslands, canyons, and riparian areas.

Morphological trends:—Perennial herbs or woody subshrubs, leaves opposite, blades lanceolate to ovate or elliptic, bases often cordate to truncate, petiolate, heads often in paniculiform arrays, nodding or erect, involucre bracts strongly imbricate, florets 15–35 or numerous per head, pappus bristles mostly barbellate (sub-plumose to plumose in B. hinckleyi and B. brachyphylla ). Taxa found primarily in pine-oak habitats ( B. orizabensis , B. pendula , B. argyrolepis , B. secundiflora , B. aramberrana , B. tomentella , B. cavanillesii ) all have nodding heads, although B. palmeri appears to be an exception in having erect heads despite favoring pine-oak habitats. Brickellia oliganthes and B. paniculata of low to mid elevations (tropical deciduous forests) have erect heads. Only B. lewisii and B. worthingtonii have clearly nodding heads among those taxa which compose the B. lewisii clade; B. wislizeni occupies pine-oak forests in Chihuahua and northern Durango, but has erect heads.

Taxonomic issues:—The circumscription and relationships of the morphologically and genetically variable B. pendula need further assessment; Turner (1997) suggested it has a close relationship with B. argyrolepis , but in the molecular phylogenetic analysis samples of B. pendula were placed near B. orizabensis and B. paniculata . Another morphologically variable species needing detailed study is B. lemmonii (four varieties recognized by Turner 1990, 1997) which was not shown to be monophyletic in results reported by Schilling et al. (2015). The relationships and circumscription of B. hinckleyi and B. brachyphylla are also problematic; B. hinckleyi var. terlinguensis (Flyr) B.L. Turner was first treated as a variety of B. brachyphylla .