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The phytomelanin layer in traditional members of Bidens and Coreopsis and phylogeny of the Coreopsideae (Compositae)

Authors

  • Mesfin Tadesse,

    1. Dept of Evolution, Ecology and Organismal Biology, Museum of Biological Diversity, The Ohio State Univ., 1315 Kinnear Road, Columbus, OH 43212, USA.
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  • Daniel J. Crawford

    1. Dept of Evolution, Ecology and Organismal Biology, Museum of Biological Diversity, The Ohio State Univ., 1315 Kinnear Road, Columbus, OH 43212, USA.
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M. Tadesse, Dept of Evolution, Ecology and Organismal Biology, Museum of Biological Diversity, The Ohio State Univ., 1315 Kinnear Road, Columbus, OH 43212, USA. E-mail: tadesse.1@osu.edu

Abstract

The phytomelanin layer on the pericarp of cypselae (achenes) of many members of traditional Bidens and Coreopsis, both considered polyphyletic, was studied with the help of scanning electron (SEM) and light (LM) microscopes. It is found to be more prominent in taxa kept within Bidens than in Coreopsis. The black ‘peg-like’ phytomelanin found in traditional members of Bidens is also found in some members of Coreopsis. Some traditional members of Coreopsis display distinctive pericarp morphology but lack phytomelanin. The pericarp in Bidens is striated, i.e. it is interrupted by longitudinal bands of parenchyma through which the embryo emerges during seed germination. No striation was found in cypselae of traditional Coreopsis. Emergence of the seed in taxa with this type of pericarp morphology is observed to be by rupturing the carpel wall along the sutures. Characteristic morphology of the phytomelanin layer and other cellular secretions on the pericarp in representative species of these genera and segregates as well as the probable adaptive value of this layer and that of the parenchyma is discussed. Coreopsis sect. Tuckermannia (Nutt.) Blake, C. sect. Pugiopappus (A. Gray) Blake, and C. sect. Euleptosyne (A. Gray) Blake, are elevated to the genus Leptosyne DC., while Coreopsis sect. Electra (DC.) Blake is returned to Electra DC. A key to the segregate genera and the remaining sections of Coreopsis as well as new combinations and synonyms are provided.

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