Comparative pollen morphology and taxonomic considerations in Eriocaulaceae

Pollen morphology of 55 species from 10 of the 11 currently recognized genera of Eriocaulaceae (Actinocephlaus, Blastocaulon, Eriocaulon, Lachnocaulon, Leiothrix, Paepalanthus, Philodice, Rondonanthus, Syngonanthus and Tonina) has been studied using light and scanning electron microscopy. Species presented pollen grains in monads, which were small (Blastocaulon, Lachnocaulon, Philodice and Tonina) to medium sized (Eriocaulon, Leiothrix and Rondonathus), while the other genera presented pollen grains in both size classes. Apertures were sulci, mainly forming spirals, in one, two or three units in different features. The exine is thin, less than 3 µm in thickness; there are two types of supratectal processes, granulose and spinulose. The spinulose processes can be acute or obtuse, with side walls being straight, concave or convex. The pollen characteristics do not support the segregation of the genera Actinocephalus and Paepalanthus. The Syngonanthus species are the only ones to present two apertural patterns: spiraperturate and 2-zonasulcate. The spiraperturate species of Syngonanthus also possess similar characteristics to the genera Actinocephalus and Paepalanthus, so much so that it is not possible to distinguish them. The pollen morphology data support taxonomic arrangements at different levels: the separation of the family into two subfamilies, Eriocauloideae and Paepalanthoideae, the separation from Syngonanthus of sect. Eulepis by its 2-zonasulcate pollen grains and the segregation of Tonina fluviatilis, due to its grooved spines, into its own genus.