A Peculiar Amphitropical Genus of Paniceae (Poaceae, Panicoideae)

The genus Louisiella (Poaceae, Paniceae) is reviewed. This African monotypic genus was originally circumscribed on the basis of morphological characters. Recent phylogenetic studies have shown its affinity with an American species of Panicum, P. elephantipes. Molecular, morphological, and anatomical characters of Louisiella fluitans and P. elephantipes were analyzed. Both species share vegetative and reproductive characters, including habit, ligules, blades, inflorescence, and spikelet features, such as a reduced lower glume, lanceolate upper glume and lower lemma both longer than the upper anthecium, lower palea reduced or absent, and lower flower absent, upper anthecium indurate, and a caryopsis with a linear hilum. Anatomically, both taxa are Kranz of the PS-subtype, with specialized chloroplasts on the outer parenchymatous sheath. The molecular phylogenetic analysis also corroborates the relationship between these species, with a 100% bootstrap support. As a result, we conclude that P. elephantipes has to be transferred to Louisiella, making that genus amphitropical in distribution. Affinities of Louisiella with other genera of Paniceae are also discussed. Finally, two lectotypes are designated for Panicurn fistulosum and Digitaria megapotamica.