Seed morphology and its relationships with phylogeny, lifeform and distribution of African orchid species

Abstract

Abstract Variation in orchid seed size and shape can be linked to phylogenetic relationships, habitat preferences, germination behaviour or dispersal strategies. To investigate this, we compared 45 orchid species from 29 genera collected across different localities in Cameroon using optical microscopy. We categorized each species according to lifeform (38 epiphytic vs. 7 terrestrial), altitudinal range (11 mountain vs. 34 lowland) and geographic distribution (28 widespread vs. 17 range-restricted). We analysed seed morphology using phylogenetic signal tests, analysis of variance and principal component analysis. Our results confirm a clear distinction between epiphytic and terrestrial species, with intermediate morphologies observed in genera encompassing species with both lifeforms ( Cynorkis, Graphorkis, Habenaria and Liparis ). Certain traits, such as seed length and seed air space, show a strong phylogenetic signal, suggesting that these traits are more linked to ancient evolutionary history than to recent ecological adaptation. Among the 38 epiphytic species, no consistent relations were found between seed traits and either geographic range or altitudinal distribution. Our findings suggest that the variation observed in seed morphology among African orchids is influenced more by phylogenetic relationships than by present-day distribution.