Inferring Taxonomic Relationships among Rhizophora Species in Nigeria Using Leaf Morphometrics and Pollen Information

Abstract

Leaf and pollen samples of Rhizophora individuals and the associated soil and water physico-chemical parameters were conducted to generate taxonomic relationships. Samples were collected across Niger Delta region between 2013-2016. Although, application of multiple nuclear genes to the molecular phylogeny, population genetics and hybrid identification has been used. However, there are no sufficient molecular markers to address these topics. Three hundred and sixty four (364) Rhizophora samples were obtained in all. Leaf length, leaf width, stipule length, petiole length, number of lateral nerves, space between lateral nerves, distance between internodes, distance of mid rib away from symmetry and number of foliages per twig was used to obtain morphological relationships. Standard laboratory methods were adopted. Morphologically, the result established five statistically significant differences in Rhizophora Operational Taxonomic Units (OTUs) with leaf length, stipule length, number of lateral nerves and distance between lateral nerves as characters that delimited one Rhizophora unit from the other. The study also proved specific character that separated each OTU and locations occupied by each. The result of the pollen analysis was used as complimentary evidence to morphology. The apertural morphoforms was tricolporate, while differences exist in exine patterns and pollen shapes. The application of ANOVA and Principal Component Analysis showed OTUs 1 and 2 as significantly different. Although, OTUs 3, 4 and 5 showed statistical difference among themselves, cluster analysis revealed close affinities. The influence of soil and water physico chemical parameters further confirmed the taxonomic distinctness of OTUs 1 and 2 and similarities among OTUS 3, 4 and 5. The finding is in contrast to the widely held notion that only three putative Rhizophora species exist in Nigeria. Genetic research into these five OTUs is recommended.