Pollen morphology of the tribe Morindeae (Rubiaceae)

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Abstract
This investigation represents a detailed account of the pollen morphology of 32 species from 10 genera in the tribe Morindeae (Rubiaceae). Light microscopy, scanning electron microscopy, and, for three species, transmission electron microscopy are used. Seven pollen types are established and described and a key to their identification constructed. The tribe is eurypalynous; with some exceptions the pollen grains are tricolporate, suboblate to spheroidal and medium-sized and have a reticulate or microreticulate sexine. The pollenmorphological variation within the different genera is discussed. Most of the genera are stenopalynous, whereas Morinda, in particular, is markedly eurypalynous. The importance of pollen morphology for the taxonomy in Morindeae is evident and this and other features are compared, in order to elucidate the problems of generic delimitation. The genera Appunia and Pogonolobus are re-established on the basis of pollen morphology and several other features.

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