Colleter morphology in Pavetta, Neorosea and Tricalysia (Rubiaceae) and its relationship to the bacterial leaf nodule symbiosis

Abstract

Buds removed from herbarium specimens were processed for light microscopic examination of colleter form and anatomy. Most Pavetta species have dendroid colleters and bacterial leaf nodules, a correlation also found in an earlier study of Psychotria. Colleters of Neorosea, another genus with leaf-nodulated species, are more like the standard rubiaceous type that predominates in the family except that they have irregular, bulging epidermal cells. Tricalysia, a nodule-free genus closely related to Neorosea, shows a range of colleter form from standard to dendroid, and some species have the Neorosea type of colleter. Such morphological correlation between the bacterial leaf nodule symbiosis in Pavetta and Psychotria and dendroid colleters may indicate a chemical change in colleter secretion. Apart from their involvement with the bacterial symbiosis, rubiaceous colleters have now been shown to vary sufficiently in certain taxa to be considered as additional useful taxonomic characters.