Infrageneric phenetic relations in new world Panicum (Poaceae: Panicoideae: Paniceae): a numerical analysis

Abstract

Numerical studies based on 64 characters placed 188 American species of the genus Panicum L. in 23 sections clustered in five major groups. The same major groups were obtained when the five characters that define the subgenera were excluded from the analyses. Groups 1 and 2 included C4 species. Species with an outer parenchymatous sheath in group 1 corresponded to subg. Panicum, whereas species with a single mestome sheath in group 2 corresponded to subg. Agrostoides. Group 3 included the intermediate C3–C4 species belonging to subg. Steinchisma. C3 sections were clustered together but arranged in a different way than previous classifications. Group 4 included sections from subg. Phanopyrum with basic chromosome number x = 10, whereas group 5 included the other sections of Phanopyrum with x = 9 together with sections from subg. Dichanthelium also with x = 9. The two subgroups of subg. Phanopyrum are not only different in chromosome number but also in inflorescence type and upper anthecium ornamentation. On the other hand the x = 9 sections of Phanopyrum remain in the same cluster with sections from subg. Dichanthelium in numerical analyses where basic chromosome number is removed. These results suggest the possibility of sinking Dichanthelium into Phanopyrum and then split the latter when more cytological data become available. Kranz syndrome and basic chromosome number were the characters with the highest contribution to the delimitation of the major groups. On the basis of these results different existing hypotheses on the classification of the genus Panicum are discussed. Key words: Panicum, numerical taxonomy.