Systematics and reproductive biology of the genus Witheringia l'Her. (Solanaceae)

Date of Completion

January 2001

Keywords

Biology, Botany

Degree

Ph.D.

Abstract

Field and greenhouse observations and measurements, herbarium specimen analyses and chromosomal and reproductive biology studies involving over 5,000 specimens were done in order to understand the phylogenetic and evolutionary patterns of the genus Witheringia. Plants of Witheringia are mostly tropical herbs and shrubs, distributed from Mexico to Bolivia, usually found growing between sea level and 2200 m, but with a concentration of species in Central America, especially in Costa Rica and Panama (10 of 16 spp.). Witheringia solanacea, the type species, is also the most widespread, with an ample geographic distribution from southern Mexico to southern Bolivia and several Caribbean islands and an altitudinal range from 0–1900 m. Floral characteristics, including pollen quantity, size and viability, number of ovules and seeds imply a trend toward outcrossing, and insect pollination. These species further avoid selfing by dichogamy; all the studied taxa proved to be protogynous. Observations on flowers in situ at three biological reserves in Costa Rica showed bees to be the dominant floral visitors and presumed pollinators. All species of Witheringia had a chromosome number of n = 12. A total of 1466 reciprocal and self crosses was performed among 39 individuals of 14 species of Witheringia, and related genera, Brachistus, Cuatresia and Capsicum. These experiments confirmed that self incompatibility characterizes all species of Witheringia except two accessions of W. solanacea (from Costa Rica and Panama), which are self compatible. The only hybridization yielding viable seeds involved W. solanacea and W. asterotricha (reciprocal crosses were successful). Results of a phylogenetic analysis rearranged the generic boundaries of Witheringia by transferring three species to two different genera. A second analysis with the three species removed yielded strong support for Witheringia as a monophyletic genus. Brachistus, another tropical American genus proved to be the sister taxon of Witheringia. A key to Witheringia and related genera is provided. Furthermore, a key and detailed descriptions of Witheringia and its 12 species complement this biosystematic study. ^

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