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. chapadense, sp. nov., from the campo rupestre habitats of Goias, Brazil. Altoparadisium chapadense is illustrated and fully described morphologically and anatomically. It is extremely unusual in the Paniceae in possessing only two spikelet bracts and in having spikelet reduction from the apex as well as the base. The bracts are interpreted to be homologous to an upper glume and lower lemma. The only flower is interpreted to be homologous to the upper flower of a typical panicoid spikelet. It is a C4grass with Kranz anatomy, distinctive Kranz cells, and typical panicoid bicellular microhairs. In order to establish the phylogenetic relationships of Altoparadisium, it was included in a cladistic analysis of Arthropogon and related genera. We conclude 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 illustrated for the first time; (3) Arthropogon bolivianus and A. rupestris are reduced to varieties of Altoparadisium chapadense; (4) Arthropogon piptostachyus 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 unresolved, such a new name is not yet proposed. The recircumscribed genera Arthropogon and Achlaena are briefly summarized, and a key to their species and varieties is provided.