Branched Foliar Trichomes of Lobelioideae (Campanulaceae) and the Infrageneric Classification of Centropogon

The morphology of branched foliar trichomes in Lobelioideae (Campanulaceae) was studied via scanning electron microscopy. Trichomes of this type are found only in the Neotropical endemics Burmeistera, Centropogon, and Siphocampylus, and in the Hawaiian endemic Cyanea. The 37 species examined included all species with branched trichomes in Burmeistera, Centropogon sect. Burmeisteroides, Centropogon sect. Niveopsis, Centropogon sect. Wimmeriopsis, Cyanea, and Siphocampylus, plus about one-fourth of the 100 species comprising Centropogon sect. Siphocampyloides. Trichomes observed conformed to eight structural types. Dendritic, multangulate, multangulate-dendritic, echinoid, and furcate hairs were found only in Centropogon sect. Siphocampyloides, Cyanea, and Siphocampylus. Echinoid-dendritic hairs were confined to Centropogon sect. Burmeisteroides, stellate hairs to Centropogon sect. Wimmeriopsis, and multiseriate-multangulate hairs to Burmeistera and Centropogon sect. Niveopsis. Within Centropogon, the distribution of trichome types is consistent with the currently accepted classification of the genus. Correlations with other data, both morphological and molecular, suggest that branched trichomes have evolved in the subfamily repeatedly, perhaps as many as 11 times.