Spore characterisation and its taxonomic significance in ferns from Lagos State, Nigeria

Abstract The gradual disappearance of ferns due to biodiversity loss occasioned by anthropogenic activities and global climate change necessitated the need to document and study palynologically pteridophytes in Lagos State. Their peculiar habitat is fast declining in many urban centres of the world, including Nigeria. Previous studies in Nigeria mainly addressed their distribution, with limited reports on their morphology and systematic significance. Hence, we conducted a field survey and characterised the spore morphology of the encountered ferns in Lagos State, Nigeria, using light microscopy (LM) and scanning electron microscopy (SEM). We recorded nine species belonging to nine genera and five families. The studied species varied in spore size, shape, and ornamentation. Spores’ sizes ranged between 30 μm × 32 μm in Nephrolepis biserrata and 122 μm × 127 μm in Ceratopteris cornuta. Symmetrically, they were bilateral or radial, and ranged in size between very large, large, and medium. Despite marginal differences in polar to equatorial diameter ratios (P/E ratios), the oblate-spheroidal shape class was found to be a synapomorphic character. We observed relationships between the spore shape and the corresponding aperture type. SEM revealed different spore ornamentation types – tuberculate, canaliculate, rugate/rugulate, reticulate, verrucate, tuberculate, and echinate. Our findings propose the potential use of spore P/E ratio and SEM as taxonomic diagnostic tools in Pteridophyte systematics. However, further studies with more representative species are needed to evaluate the factors influencing spore morphology and its taxonomic significance. Overall, this study provides insights into the systematics of ferns in Lagos State and would aid fern identification in palynology and palaeopalynology.