Floral structure and palynology of Podostemum weddellianum (Podostemaceae: Malpighiales)

The family Podostemaceae is exceptional among angiosperms because of its uncommon biology and morphology, the absence of double fertilisation and endosperm, and the obscure distinction between root, stem, and leaf. The highly modified morphology produced by reductions and specialisations is reflected in the multiple positions that the Podostemaceae has occupied in different classification systems. In the family, structural studies are mainly related to the vegetative body. In the genus Podostemum, structural data are related to the development and embryology of Podostemum ceratophyllum Michx., which, with P. weddellianum, has pre-anthesis cleistogamy. P. weddellianum is analysed for the first time with regard to floral structure and palynology. The presence of silica in the spathella, the apical septum in the ovary, dyads and pseudomonads, unimodal embryo sac and chasmogamous flowers with the possibility of self-pollination contribute to the characterisation of the Podostemoideae and the search for relationships among Podostemaceae and the clusioids.