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Faculty for Biology, Chemistry, and Earth Sciences

Department of Plant Systematics: Angiosperm Working Group - Prof. Dr. Sigrid Liede-Schumann

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Wolff, D; Liede-Schumann, S: Evolution of flower morphology, pollen dimorphism, and nectar composition in Arcytophyllum, a distylous genus of Rubiaceae, Organisms, Diversity & Evolution, 7(2), 106-123 (2007), doi:10.1016/j.ode.2006.02.005
A phylogenetic study of Arcytophyllum based on ITS was conducted and compared with an earlier study based on cpDNA. The position of the widespread A. thymifolium as sister to all other species was confirmed and several well-supported clades could be retrieved. The Central American A. lavarum is well embedded between exclusively or predominantly South American species. To understand the expression of heterostyly in the genus, we analyzed inter- and intraspecific variation in floral morphology, nectar, pollen-ovule-ratio and seed set of ten species in eleven populations. Stigma and anther levels differed significantly between the morphs in the species/populations investigated except for A. filiforme. Different expressions of heterostyly in Arcytophyllum seem independent of phylogenetic relationships. Nectar sugar composition was similar between the morphs. Nectar of most species presented a larger proportion of hexoses than of sucrose, only the most derived species, A. macbridei and A. vernicosum, have higher sucrose proportions. There is a significant positive correlation between corolla tube length and the proportion of sucrose. Pollen dimorphism, both with regard to the number (long-style > short-style) and to the size (short-style > long-style) was observed in all taxa investigated except for A. filiforme. According to the pollen-ovule-ratios the breeding systems range from facultative autogamy to facultative xenogamy, independent of phylogenetic relationsship. The main floral visitors of the species studied were Hymenoptera, Diptera and Coleoptera. Seed production did not differ significantly between the morphs in eight of the eleven species/populations investigated. There is, however a tendency in all species/populations (except for A. macbridei Peru) that the short-styled morph had a higher percentage of seeds per ovule indicating that the short-styled morphs display higher female reproductive success.
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