DOI: 10.3724/SP.J.1002.2008.00041

Journal of Systematics and Evolution 2008/46:1 PP.41-52

A hypothesis on cupule evolution and the evidence from molecular phylogenies and fossils

The cupule is the most distinguishable character of the Fagaceae and has been the focus of much research. Many hypotheses have been proposed for the origin, evolution and morphological features of the cupule. These were based on different types of evidence, but here we used molecular phylogenetic and fossil evidence. Our results supported the view that cupule valves originated from the outermost branches of the dichasium, and that cupules of the Fagaceae were distinct from other cupule-like organs with perianth origins in Fagales. There were three models of cupule evolution, each characterized by distinct evolutionary tendencies, single, dual and multi-directional respectively. Based on these models, we reconstructed the cupule's evolution using the consensus of four recent molecular phylogenies from different DNA fragments. Our results indicated that cupules had a monophyletic origin and that the Fagus cupule, with four cupule valves enclosing two triangular acorns, represented the ancestral type, the Trigonobalanus cupule was the inferior-ancestral type, and the Chrysolepis cupule which possesses inner valves, shared a common ancestor with other roundish cupules. Our conclusions are also unequivocally supported by fossil evidence, with affinity of extant homologous cupule. The consensus from four molecular phylogenetic hypotheses along with the age of fossil cupules that are similar to extant Fagaceae taxa indicate that the cupule evolved in multi-directions, and that the small triangular, narrow winged fruits surrounded by a dehiscent cupule was plesiomorphy, and that a bigger roundish fruit surrounded by an indehiscent cupule was apomorphy. All these results provide the new evidence to explore evolution and phylogeny of Fagaceae.

Key words:cupule, evolutionary hypotheses, Fagaceae, fossil, molecular phylogeny, origin.

ReleaseDate:2014-07-21 14:10:09

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