Oral Paper

         Phylogenomics

Phylogeography of an endemic Himalayan-Tibetan-Hengduan lineage of Lonicera (Caprifoliaceae)

Presenting Author
Mansa Srivastav
Description
Isoxylosteum is a small clade of Lonicera that is endemic to the Himalayan-Tibetan-Hengduan region. Five species complexes, containing from 5-11 species, have been recognized in this taxonomically difficult lineage. Despite its small size and restricted distribution, Isoxylosteum exhibits enormous ecological and morphological diversity. Its species are united by white to pink, radially symmetrical flowers, but they show exceptional variation with respect to nearly every other trait. The ovaries of different species may be completely free, or partially to fully fused; the bracteoles of adjacent flowers may fuse at the base of the flower pair or all four bracteoles of the pair may fuse to form a partial cupule; the style and stigma may be exserted or deeply seated within the corolla tube; the fruits may be blue, orange or red; and branches may or may not form thorns. Dramatic morphological variation can be found even within presumptive species. For example, within the Lonicera angustifolia complex, plant height can vary from two centimetres to nearly two meters, and the two flowers within a cyme can be free or fused completely with each other. Isoxylosteum taxa occupy a wide range of habitats from wet and dry temperate forests to cold deserts and wet alpine areas, over a wide elevational range. Due to such drastic ecological and morphological variation, some 25 species, subspecies, and varieties have been described. However, it has not been clear if these are just minor ecological or geographic variants or independently evolving lineages that deserve species status. Here we present a phylogeographic analysis of the clade based on collections from ~100 populations spanning its wide longitudinal range. We combine this with morphometric analyses and species distribution modelling to trace character evolution and resolve species boundaries. It appears that all populations and proposed taxa sort into four well supported clades, corresponding to four of the five proposed species complexes. Our analyses also shed light on biogeography and biome evolution in the Himalayan-Tibetan-Hengduan region.