Morphological evidence for an extended tribe - Coccocypseleae (Rubiaceae-Rubioideae)

Coccocypselum is a small neotropical genus of creeping herbs belonging to t he Rubiaceae (Rubioideae). A recent macromolecular study suggested a previo usly unknown relationship between Coccocypselum and two other neotropical g enera, Declieuxia and Hindsia, but the morphological evidence for this rela tionship was obscure. In the present paper, morphological characters suppor ting the conclusions from macromolecular data are presented. The most impor tant similarities between Coccocypselum, Declieuxia, and Hindsia are found in their pollen and stipule morphology. Pollen of the three genera share a typical exine ornamentation, called a complex reticulum, which consists of a psilate suprareticulum and spinulate infrareticulum. In some specimens of Hindsia longiflora, a transitional stage between a complex reticulum and a simple, spinulate reticulum is encountered. The interpetiolar stipules of Hindsia, Declieuxia and Coccocypselum have an identical basic structure: th ey bear a central, colleter-tipped awn that extends downwards to the next n ode as a distinct stem ridge. Some less conspicuous similarities of habit, calyx, and corolla are also discussed. The morphological data are, in part, confirmed by distributional data, Declieuxia and Hindsia having a remarkab ly congruent centre of diversity in the southeast of Brazil. It is conclude d that the macromolecular data, combined with this new morphological and di stributional evidence, justify an extended tribe Coccocypseleae, comprising the genera Coccocypselum, Hindsia, and Declieuxia.