| A monographic treatment, based on field and herbarium studies, is provided for Paepalanthus subg. Xeractis. This represents the first monographic study conducted of this large genus since Ruhland's (1903) treatment. Subgenus Xeractis is distinguished by its involucral bracts usually exceeding the capitulum and by the male corollas hairy within. Some of its species are found to show markedly primitive characters such as leaflike bracts, deeply divided male corollas, and sepals with stomata. On the basis of floral characters, six species are removed from the subgenus. Five species, four varieties, and one form are newly described, with the total number of taxa recognized totalling 27 species, eleven varieties, and two forms. These are grouped into four newly described sections and two series, which are distinguished on the basis of habit, leaf anatomy, involucral bract color, and floral pubescence and pigmentation. In addition, 12 putative hybrids were collected in the field or identified from herbarium material. Substantial introgression was found in one of these hybrid cases.;Paepalanthus subg. Xeractis is wholly endemic to the Serra do Espinhaco of Minas Gerais, Brazil, a mountain range about 370 km long, which supports high diversity and endemism in many angiosperm taxa. Most species have very small ranges, and the collective patterns of their distribution suggest a division of the Serra do Espinhaco into four floristic regions: the Diamantina plateau; the northern Serra do Cipo; the southern Serra do Cipo; and the southern Serra do Espinhaco. The species diversity is highest and the species distributions smallest in the very poor quartzitic soils of the Serra do Cipo. Within the Serra do Cipo, the species occurring in seasonally wet habitats on shallow or poorly drained soils are the most problematic, characterized by reticulate variation patterns, and otherwise showing indications of recent diversification. |
