A monograph, based on field and herbarium studies, is provided for Paepalanthus subg. Xeractis, which is distinguished by involucral bracts usually exceeding the capitulum and by male corollas hairy within. Some of the species show markedly primitive characters, such as leaflike bracts, deeply divided corollas in male flowers, 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: P. anamariae, P. clausenii, P. digitiformis, P. lanuginosus, P. revolutus, P. augustus var. picensis, P. mollis var. itambeensis, P. superbus var. gracilis, P. uncinatus var. rectus, and P. chlorocephalus f. parviflorus. In addition, three new combinations are proposed: P. argenteus var. elatus, P. calvulus, and P. superbus var. niveo-niger. Subgenus Xeractis comprises twenty-seven species, including eleven varieties and two forms. These are grouped into the newly described sections Chrysostegis, Gymnostegis, Pleurophyllon, and Xeractis, the last divided into series Albidi and Fuscati.
The sections and series are distinguished on the basis of habit, leaf anatomy, involucral bract color, and floral pubescence and pigmentation. In addition, twelve putative hybrids were collected in the field or identified from herbarium material. Substantial introgression was found in one of these instances of hybridization. Subgenus Xeractis is wholly endemic to the Serra do Espinhaço of Minas Gerais, Brazil, a mountain range about 370 km long, which supports high diversity and endemism in many angiosperm taxa. Most species have a very small range, and the collective patterns of their distribution suggest a division of the Serra do Espinhaço into four floristic regions: the Diamantina plateau; the northern Serra do Cipó; the southern Serra do Cipó; and the southern Serra do Espinhaço. The species diversity is highest ancnd the species distributions narrowest in the very poor quartzitic soils of the Serra do Cipó. Within the Serra do Cipó, the species occurring in seasonally wet habitats on shallow or poorly drained soils are the most problematic; they are characterized by reticulate variation patterns and otherwise show indications of recent diversification.
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