Abstract
Pteris (Pteridaceae) spores are usually trilete and can be distinguished by the perine ornamentation. The systematic value of spore morphology in Pteris is unclear, especially based on the renewed infrageneric classification of Pteris. In the present study, we used scanning electron microscopy (SEM) to understand spore characters in 57 Pteris species, one Onychium species, and two Astrolepis species; 40 species are reported here for the first time. The observed spore characters combined with published spore data, totaling 100 species from 16 sections of Pteris, were mapped onto a reconstructed phylogenetic tree. Seven characters (five proposed in previous studies), including an equatorial flange, laesural ridges, proximal ridges, distal ridges, tubercula on distal faces, coarse reticula on distal faces, and a row of extervermiculi between the distal face and equatorial flange, were analyzed to investigate spore morphology evolution in Pteris. However, the results showed no synapomorphies with other genera in Pteridaceae. Most of the characters were found to have arisen independently several times in different lineages or were even frequently reversed. Equatorial flanges and tubercula on distal faces are plesiomorphies and present in most Pteris species. Overall, the application of spore morphology in section circumscription is limited. Thus, we suggest combining spore morphology with leaf characters for Pteris infrageneric classification.
Highlights
Phylogenetic studies of the genus Pteris (Pteridaceae) have revealed its major lineages
The topology obtained was similar to that in previous studies [3]; the 180 Pteris species were grouped into three major clades with strong support (BPP = 1; Figs 1 and 2), corresponding to three subgenera, Campteria, Platyzoma, and Pteris [2]
Equatorial flanges, tuberculate distal faces, and reticulate distal faces show the fewest transitions among the seven selected characters
Summary
Phylogenetic studies of the genus Pteris (Pteridaceae) have revealed its major lineages. The monophyly of the genus Pteris has been confirmed using six cpDNA and one nuclear markers, and P. platyzomopsis Christenh. Br.) is included in this genus [1]. Pteris is classified into three subgenera and 16 sections [2]. Most leaf characters were shown to have arisen several times in different lineages or were even frequently reversed [3]. Homoplasy results show that the leaf morphological characters cannot circumscribe sections well, even when combined with the geographic distribution
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