FLORAL ANATOMY of XYRIDS (POALES): CONTRIBUTIONS TO THEIR REPRODUCTIVE BIOLOGY, TAXONOMY, and PHYLOGENY

Xyridaceae, Eriocaulaceae, and Mayacaceae form the xyrid clade, which is weakly supported in Poales. The floral anatomy of xyrid species was studied, to contribute to the understanding of the relationships within the group. Both Eriocaulaceae and Xyridaceae have petals with elongated epidermal cells with straight walls, epipetalous stamens, staminodes, anthers with longitudinal dehiscence, an endothecium with band-like thickenings, and a style vascularized by the dorsal carpellary bundles; these characteristics thus corroborate the close relationship of these groups indicated by phylogenetic analyses. Mayacaceae is distinguished by the presence of papillose epidermal cells in the petals, a reduced inner whorl of stamens, poricidal anthers, an endothecium lacking thickenings, a style and stigma vascularized by the dorsal and ventral carpellary bundles, and the presence of an obturator in the ovary wall. A reduction in the inner whorl of fertile stamens also occurs in Juncaceae and Cyperaceae, linking Mayacaceae to the cyperids. The stylar appendages of Orectanthe (Xyridaceae) have been shown to be nectariferous and anatomically similar to those of Abolboda, differentiating these two genera from Xyris (Xyridoideae) and confirming their placement in Abolbodoideae. Stylar appendages also occur in Eriocaulaceae, with the same function, position, and vascularization, and are therefore homologous structures, reinforcing the phylogenetic proximity between Eriocaulaceae and Xyridaceae.