Spore morphology and wall ultrastructure of Trachypteris species (Pteridaceae)

Trachypteris is a small genus consisting of four species native to America and Madagascar: Trachypteris induta, T. pinnata, T. gilliana, and T. drakeana. The spores of the genus were studied using light microscopy and scanning and transmission electron microscopy. They are trilete, triangular to globose, with equatorial diameter of 29-58 mu m and polar diameter of 26-53 mu m. The exospore is 0.5-1.1 mu m thick, plane, and two-layered. The perispore is 0.3-6.8 mu m thick and two-layered. Depending on the species, two different ornamentations were observed: cristated with partially fused cristae, and ridged with partially fused ridges, forming an incomplete reticulum. Globules immersed in the perispore were occasionally observed. The systematic value of the Trachypteris spores is discussed, and their morphology and ultrastructure are compared with those of other related cheilanthoid ferns. The palynological characteristics presented here may be useful for phylogenetic studies within the Pteridaceae, and particularly within the cheilanthoid ferns.