Evolution of epiphytism in Solanaceae

Abstract

Epiphytes are non-parasitic plants that live above the ground without a connection to the soil. Epiphytes comprise about 10% of the world's vascular flora and show various adaptations to living without access to soil water, including aerial roots, tank life form, CAM photosynthesis, and different nutrient uptake efficiency rates. Details of the evolution of these adaptations and how and when epiphytes evolved remain poorly understood. This thesis explores the evolution of epiphytic life form in Solanaceae, where a minimum of three independent origins of epiphytic life form is found. Most of the c. 90 species of epiphytes in Solanaceae are found in the tribe Solandreae, including c. 80 species. Many of these species remain undescribed or taxonomically poorly understood. As part of the study, I built a robust and densely sampled phylogeny of Solandreae based on complete plastome data, showing that the group consists of 11 strongly supported clades corresponding to 9 previously identified genera and two undescribed genera (Chapter 2). The morphological evolution of 14 characters is discussed, including the epiphytic life form that has evolved a minimum of three times independently. Chapter 3 provides a synopsis of one of these 11 genera, Sarcophysa, with a morphological circumscription of the genus, distribution maps and taxonomic notes for all 20 species, and 14 new nomenclatural combinations required. Five new species remain to be described in the genus, and details of these are listed. Chapter 4 describes a new genus Doselia based on the molecular phylogenetic results, with three new combinations and one new species description, full species descriptions, distribution maps and a key to all species. Finally, Chapter 5 explores the evolution and diversity of the pollination syndromes using morphometrics in a phylogenetic context combined with field studies of flower visitors. Three pollination syndromes are found in the tribe: pollination by bats, bees, and hummingbirds. There is likely to be an additional group of “mixed” pollinated plants. All pollination syndromes have evolved multiple times independently, with frequent switching observed between the syndromes.

Altogether, this thesis provides new morphological, molecular phylogenetic, field-based data on the tribe Solandreae and demonstrate one of the most remarkable cases of floral evolution across Solanaceae. A total of 20 species remains to be described in the tribe and much more remains to be learnt from these silent kings and queens of the cloud forest canopies across Central and South America.