The establishment of the new genus Altoparadisium and a reevaluation of Arthropogon (Poaceae, Paniceae)

Altoparadisium is described as a new genus of Paniceae based on A. chapaden se, sp. nov., from the campo rupestre habitats of Goias, Brazil. Altoparadi sium chapadense is illustrated and fully described morphologically and anat omically.; It is extremely unusual in the Paniceae in possessing only two s pikelet bracts and in having spikelet reduction from the apex as well as th e base. The bracts are interpreted to be homologous to an upper glume and l ower lemma. The only flower is interpreted to be homologous to the upper fl ower of a typical panicoid spikelet. It is a C-4 grass with Kranz anatomy, distinctive Kranz cells, and typical panicoid bicellular microhairs. In ord er to establish the phylogenetic relationships of Altoparadisium, it was in cluded in a cladistic analysis of Arthropogon and related genera. We conclu de that: (1) Arthropogon as traditionally circumscribed is polyphyletic; (2 ) Arthropogon scaber is the sister species of Altoparadisium chapadense; it is therefore transferred to this genus as Altoparadisium scabrum and illus trated for the first time; (3) Arthropogon bolivianus and A. rupestris are reduced to varieties of Altoparadisium chapadense; (ii) Arthropogon piptost achyus is recognized as originally described, i.e., as the monotypic genus Achlaena; (5) Arthropogon lanceolatus should probably be included in a new, monotypic genus, but because its phylogenetic relationships remain unresol ved, such a new name is not yet proposed. The recircumscribed genera Arthro pogon and Achlaena are briefly summarized, and a key to their species and v arieties is provided.