Although the pollen morphology of Xyridaceae shows standard patterns that distinguish five genera, specific data of each genus are scarce or incompletely known. The pollen morphology of 17 Brazilian species of Xyris (Nematopus Section) based upon 47 specimens from Goiás and Minas Gerais States, Brazil, is presented. Micrographs of pollen grain structures were obtained using light and scanning electron microscopy. Pollen grains are characterized as monads, medium to large sized, ellipsoidal in polar view, flattened/convex in equatorial view and monosulcates. The sulci are pontoperculate and covered with an insulae type membrane. The sexine presents either a microreticulum or rugulae with perforations, and is thicker than the nexine. Although Xyris is a stenopalynous genus, characterized by monosulcate pollen grains, two groups of species were recognized based upon pollen size as well as pollen wall ornamentation features. Therefore, pollen data are of taxonomic value and useful to clarify the delimitation of the studied species.
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