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Gomphocalyx and Phylohydrax (Rubiaceae): sister taxa excluded from Spermacoceae s.s., featuring a remarkable case of convergent evolution
Author(s) -
Dessein Steven,
Andersson Lennart,
Geuten Koen,
Smets Erik,
Robbrecht Elmar
Publication year - 2005
Publication title -
taxon
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 81
eISSN - 1996-8175
pISSN - 0040-0262
DOI - 10.2307/25065305
Subject(s) - tribe , rubiaceae , biology , taxon , ovary , pollen , sister group , botany , evolutionary biology , zoology , phylogenetics , genetics , gene , clade , sociology , anthropology
The genera Gomphocalyx and Phylohydrax (Rubiaceae) have been invariably placed in the tribe Spermacoceae s.s. based on the uniovulate ovary locules and pluriaperturate pollen grains. Sequence data from the rps 16 intron and the rbcL gene here presented exclude Gomphocalyx and Phylohydrax from Spermacoceae s.s. The two genera are closely related and their nearest relatives are found among members of the former tribe Hedyotideae. This position may be surprising at first, because the growth form of Phylohydrax is similar to some observed in Spermacoceae s.s. A detailed survey of morphological and anatomical characters shows, however, that the character states of the two genera are largely consistent with the hereproposed position in Hedyotideae. The creeping growth form, the uniovulate ovaries and the pluricolporate pollen grains of Gomphocalyx and Phylohydrax are the result of convergence between this pair of genera and Spermacoceae s.s. The taxonomic position of Lathraeocarpa , sometimes considered closely related to Gomphocalyx , is also discussed.