Spikelet Structure in Panicum australiense. (Poaceae): Taxonomic and Ecological Implications

Abstract

The rhachillar stipe in Panicum australiense is prolonged and expanded below the terminal floret to form a zygomorphic body. The diaspore ultimately detaches below this body, the mature fruit falling with the body as a swollen appendage on its base. This appendage, apparently, acts as an elaiosome and the means for myrmecochorous dispersal of the caryopsis. The upper rim of the appendage is irregular, extending into two acute lobes on the ventral side of the fruit. These lobes are not homologous with the two basal fruit appendages characterizing Ichnanthus. Australian Panicum species with a rhachillar appendage like that of P. australiense probably should constitute a genus of their own.