THE MEGAGAMETOPHYTE IN ANARTHRIA (ANARTHRIACEAE, POALES) AND ITS IMPLICATIONS FOR THE PHYLOGENY OF THE POALES

The development and structure of the megagametophyte of Anarthria (Ana rthriaceae), Aphelia, and Centrolepis (Centrolepidaceae) are described . Anarthriaceae has tenuinucellate ovules and the Polygonum type of me gagametophyte development, both characters typical of the Poales. Howe ver, it lacks the anticlinally elongated nucellar epidermis and numero us large starch bodies observed in the megagametophyte of Centrolepida ceae, both characters also present in Restionaceae. This relatively ge neralized megagametophyte structure is consistent with data from the c hloroplast genome, which suggest that Anarthriaceae are not as closely related to Restionaceae as previously assumed. New data from the mega gametophyte are analyzed cladistically together with other available i nformation on the poalean families. The results show that there are tw o possible positions for Anarthriaceae: either as sister to Poaceae, J oinvilleaceae, Restionaceae, Ecdeiocoleaceae, and Restionaceae, or as sister to only the latter three families. The new data also allow a cr itical reevaluation of the phylogenetic position of Centrolepidaceae, which is either basal to the poalean clade (based on microgametophyte data), or embedded in the Restionaceae (based on anther structure and megagametophyte data).