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Morphological and ultrastructural diversity of orbicules in relation to evolutionary tendencies in Apocynaceae s.l.
Minute granules of sporopollenin, called orbicules, can be observed on the walls of tapetum cells. Vinckier and Smets (pp. 647-662) investigate orbicules in 62 Apocynaceae s.l. species and uncover a correlation between orbicule typology and evolutionary tendencies in Apocynaceae s.l. palynology.
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