Title

Preliminary Revision, Phylogenetics and and Studies of Leaf Anatomical Variation Along an Elevational Gradient in the Genus Schefflera (Araliaceae) in Sabah, Malaysia

Date of Award

4-2012

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Dr. Todd J. Barkman

Second Advisor

Dr. Steven L. Kohler

Third Advisor

Dr. Maarten Vonhof

Fourth Advisor

Dr. Gregory M. Plunkett

Abstract

The genus Schefflera of the ginseng family Araliaceae is widely distributed species in the tropics of both hemispheres and is especially abundant in mountainous areas in South America and Southeast Asia. Schefflera is the largest genus in this family and is classified into 18 subgeneric groups with more than 800 species worldwide. However, Schefflera in Borneo has never been systematically studied and remains poorly understood both taxonomically and ecologically. In this study a key is provided for 36 Schefflera species in Sabah, Malaysia and 20 new species of Schefflera are described. Previous phylogenetic work has shown that Schefflera is not a monophyletic group and there are five unrelated clades distributed throughout all the major lineages of Araliaceae. One of the clades recognized, the Asian clade, is the largest and possibly the most complex in Araliaceae with about 315 recognized species thus far. However, that study did not include any species from Borneo (except S. elliptica which is very widely distributed in Asia and S. tomentosa that can be found in west Malesia). Thus, the phylogenetic relationships of Schefflera in Borneo, (especially in Sabah and Sarawak, Malaysia), in relation to species from throughout the genus is still uncertain. Therefore, five DNA regions (two from the nuclear genome and three from the chloroplast genome); were used to test the monophyly of Schefflera in Borneo, to investigate how Schefflera taxa within Borneo are related to species from other parts of Asia and to observe how well the latest treatment for Bornean taxa reflects natural groupings of species. Phylogenetic analyses based on 226 newly generated DNA sequences showed that Schefflera in Borneo is not monophyletic and is made up of multiple lineages from within the Asian clade. Leaf anatomical and morphological traits were measured along an altitudinal gradient on Mount Kinabalu to understand how these traits vary. The result of this study showed that cuticle, palisade mesophyll, leaf thickness and LMA are strongly positively correlated with elevation.

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