Comparative pollen morphology in Luxemburgieae (Ochnaceae): exploring a palynologically neglected tribe

This study investigated the pollen morphology of Luxemburgieae (Ochnaceae). The tribe includes two genera, Luxemburgia and Philacra. Luxemburgia is endemic to Brazil, with 20 species. Philacra comprises four species, occurring in Venezuela and the northern Amazon Basin. Morphologically, the two genera differ in leaf arrangement and fruit characteristics. This study examined the pollen grains of 16 species of Luxemburgia and two of Philacra using light and scanning electron microscopy. Examination revealed that pollen grains are isopolar and shed in monads, ranging from small to medium in size. Pollen shape ranged from prolate-spheroidal to subprolate or prolate, with predominantly small polar areas. All analyzed grains were tricolporate, with long colpi and various patterns of sexine ornamentation, including bireticulate, microreticulate-foveolate, reticulate, rugulate, and rugulate-microreticulate. Hierarchical clustering and principal component analysis identified three distinct groups but did not confirm the clear separation among sections of Luxemburgia or between Luxemburgia and Philacra. Morphological characters, such as pollen size, shape, and ornamentation pattern, showed significant overlap between species.