HAUSTORIAL SYNERGIDS - AN IMPORTANT CHARACTER IN THE SYSTEMATICS OF DANTHONIOID GRASSES (ARUNDINOIDEAE, POACEAE)

The mature ovule and megagametophyte of 42 grass species (23 genera), mostly from the taxonomically troublesome subfamily Arundinoideae, was investigated. Haustorial synergids, first described from the Arundine ae, are reported for a further 26 species (ten genera) of danthonioid grasses, a group for which they appear to be synapomorphic. The evolut ion of this character and a suite of associated integument and nucella r characters is discussed. The danthonioid clade, as defined by hausto rial synergids, includes Cortaderia (often treated as nondanthonioid) but excludes a number of taxa currently contained in the Arundineae. T he full extent of the group remains undetermined, however, since sever al of its potential members remain unstudied. The data provide some in dication of phylogenetic structure within the clade. At least two of t he species of Merxmuellera studied appear to occupy a basal position, while three do not, suggesting that this genus may be paraphyletic, or even polyphyletic. Also, the reduction or absence of synergid haustor ia in Prionanthium, Pentaschistis, and Pentameris is considered to be secondarily derived and weakly corroborates the monophyly of this gene ric duster as indicated by spikelet morphology.