Spore morphology and its systematic implication in Pteris (Pteridaceae).

Area of Science:

• Botany
• Paleobotany
• Evolutionary Biology

Background:

• Pteris (Pteridaceae) spores are typically trilete, with perine ornamentation aiding identification.
• The systematic significance of spore morphology in Pteris is debated, particularly with recent reclassifications.
• Previous studies on Pteris spore morphology have yielded inconclusive results for infrageneric classification.

Purpose of the Study:

• To investigate spore character evolution in Pteris using scanning electron microscopy (SEM).
• To evaluate the utility of spore morphology in Pteris infrageneric classification.
• To map spore characters onto a phylogenetic tree for evolutionary analysis.

Main Methods:

• SEM analysis of spores from 57 Pteris species, 1 Onychium, and 2 Astrolepis species.
• Compilation of spore data from literature, totaling 100 Pteris species across 16 sections.
• Phylogenetic mapping of seven spore characters, including equatorial flange, ridges, and ornamentation.

Main Results:

• No shared derived characters (synapomorphies) were found linking Pteris to other Pteridaceae genera based on spore morphology.
• Most analyzed spore characters evolved independently multiple times or showed frequent reversals across Pteris lineages.
• Equatorial flanges and distal tubercula were identified as ancestral traits (plesiomorphies) present in most Pteris species.

Conclusions:

• Spore morphology alone has limited application in defining Pteris sections.
• Independent evolution and reversals of spore characters reduce their reliability for classification.
• A combined approach using both spore and leaf morphology is recommended for Pteris infrageneric classification.