Pollen morphology of the aquatic Brazilian endemic genus Castelnavia Tul. & Wedd. (Podostemaceae)

Abstract

The utility of pollen characteristics for taxonomic and phylogenetic analysis of most genera of Podostemaceae has barely been examined. Herein we report on the diversity of pollen structure in Castelnavia (Podostemaceae), a genus of six species endemic to central and southern Brazil. Pollen grain was shed as three-colpate, planaperturate monads and ranged from 12.5 to 22.5 μm for the polar axis and from 12.5 to 20.0 μm for the equatorial axis. All species examined had polar and radially symmetrical pollen grains. Grains from Castelnavia fluitans, Castelnavia multipartita, and Castelnavia noveloi had an oblate spheroidal shape (PD/ED), those from Castelnavia monandra and Castelnavia pendulosa were subprolate, and those from Castelnavia princeps were prolate spheroidal. The polar view was subcircular for C. monandra and subtriangular for the other species. A fastigium was observed in C. fluitans and C. pendulosa whereas a costa was present in C. multipartita and C. princeps, with the colpus margin not thickened in the former species but prominently thickened in the latter. Castelnavia monandra and C. noveloi did not have a fastigium or costa. For all species spicules occurred on the exine (microechinate sexine) and were most conspicuous on the colpus membrane. There was little correspondence between variation in pollen structure and species relationships supported by phylogenetic analysis.