A Contribution of the Palynological Criteria in Evaluating The Relationships among Some Species of Apocynaceae Sensu Lato

Abstract

APOCYNACEAE sensu lato is an interesting family with respect to pollen diversification. The pollen grains of 19 species (representing four out of five subfamilies and 18 genera) of Apocynaceae were collected and investigated using LM & SEM. The specific objective of the present study is to shed light on the different pollen morphological characters of the species under investigation and to discuss whether pollen morphology is considered an additional fundamental tool that helps in explanation of the evolutionary trend within the family. The obtained pollen data are considered diagnostic at the specific level viz. pollen association, class, polarity, sculpture, orientation and attachment of the translator. Carissa macrocrpa (Rauvolfioideae) gathered with the studied species of Apocynoideae based on the presence of porate pollen. In Cryptostegia grandiflora, the pseudo-pollinarium is considered a link between monads (as in Rauvolfioideae and Apocynoideae) and the true pollinia (as in Asclepiadoideae). Pollen criteria facilitate the construction of dendrogram, a tentative presentation of phylogenetic relationship and an artificial key to achieve further delimitation between the species under investigation and discussing the interrelationships in the view of dicta of advancement. The palynological criteria in the present study reinforced the treatment of Apocynaceae s.l. as two distinct taxonomic families (Apocynaceae and Asclepiadaceae).