Studies on structural variations of spikelets in several genera of the tribe Paniceae (Poaceae)

Abstract

The present treatment deals with different structural variations of the spikelets in the following genera of the tribe Paniceae (Poaceae): Anthaenantiopsis Mez ex Pilg., Axonopus P. Beauv., Digitaria Haller, Lasiacis (Griseb.) Hitchc., Panicum L., Paspalum L., Reimarochloa Hitchc. and Urochloa P. Beauv. This tribe shows a reductive tendency in the development of the spikelets, mainly in morphological and reproductive characters, with regards to the number of flowers and bracts of the spikelets (glumes, lemmas and paleas) and "sexuality" of the flowers. Typical biflowered spikelets is the most common pattern among the studied genera; three-flowered spikelets are always present in Panicum quadriglume (Döll) Hitchc. and Lasiacis anomala Hitchc., being occasional in Anthaenantiopsis fiebrigii Parodi, A. perforata (Nees) Parodi var. perforata, Panicum crateriferum Sohns and P. grumosum Nees. Extension of the rachilla above the upper anthoecium is common in biflowered spikelets of Lasiacis and Urochloa, being exceptional in Panicum and Anthaenantiopsis. This study also concludes that there is variation in the "sexuality" of the flowers in the spikelets: the lower flower may be perfect, staminate or neutral, while the upper one is always perfect in the biflowered ones. In the three-f1owered spikelets, the lower flower may be staminate or neutral, the medium one perfect, staminate or neutral, while the upper flower is always perfect. The occurrence of the extension of the rachilla is considered as a possible vestigial character, which represents the transition from many-flowered to few-flowered spikelets.