Dissertations, Theses, and Capstone Projects

Date of Degree

9-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Gregory M. Plunkett

Committee Members

Lawrence M. Kelly

Damon P. Little

Renuka Sankaran

Robert P Anderson

Porter P Lowry

Subject Categories

Botany

Keywords

phylogeny, niche modeling, Sciodaphyllum, Sciodaphyllum basiorevolutum, Sciodaphyllum chachapoyense, Sciodaphyllum rufilanceolatum

Abstract

Since the end of the 19thcentury, ScheffleraJ.R. Forst. & G. Forst.has been recognized as the largest and most wide-ranging genus of Araliaceae. It can be found throughout the humid tropics and subtropics, is not particularly diverse at low elevations in the warmest regions, and a few taxa extend into warm-temperate areas. As currently circumscribed, the genus contains 605 described species and many hundreds more awaiting formal description. However, a succession of phylogenetic studies have confirmed that Schefflera, as currently circumscribed,is polyphyletic, comprising five geographically centered lineages scattered across the phylogenetic tree of Araliaceae, and informally referred to as “African-Malagasy Schefflera”, “Asian Schefflera”, “Melanesian Schefflera”, and “Neotropical Schefflera”, as well as Schefflera sensu stricto, which includes the generic type, Schefflera digitata J.R. Forst. & G. Forst. Phylogenetic analyses and subsequent synoptic revisions have been produced for the Melanesian Scheffleraclade, which is now treated as a reinstated and expanded Plerandra A. Gray,and the African-Malagasy Scheffleraclade, whose species have been divided into two reinstated genera, Astropanax Seem. and Neocussonia (Harms) Hutch. Apart from the small Schefflera sensu stricto clade, which includes only eight species, the two largest clades, from Asiaand the Neotropics, still require much attention. The work presented here is an effort to improve our knowledge of the Neotropical Schefflera clade, along with a study to see how ecological niche modeling can be used to improve IUCN threat assessments focused on a single species, Plerandra elegantissima, from the Melanesian Schefflera clade.

NeotropicalSchefflera comprises 205 described species, and many more awaiting formal description. As its informal name indicates, this clade is entirely restricted to the Neotropics, with centers of diversity along the Andes, in the Guyana Shield, in Brazil, and in the Caribbean. Chapter 1 presents the taxonomic history of Schefflera. As a contribution to the great need to increase our understanding of Neotropical Schefflera, Chapters 2 and 3 focus on a morphological grouping of Andean Schefflera species that share paniculate inflorescences with distinctive globose-capitate terminal units. In Chapter 2, a phylogenetic study tests the monophyly of this “globose capitate group” and provides a trait-evolution analysis of the terminal inflorescence units found among Neotropical Schefflera species.The results show that the globose-capitate group is not monophyletic and that the globose inflorescence units originated multiple times within Neotropical Schefflera, suggesting that they are the result of convergent or parallel evolution.Chapter 3 presents evidence that this inflorescence structure characterizes a total of 91 species, 71 of which were discovered during the course of this study. Three of these new species are described in Chapter 3, along with illustrations, distribution maps, and Red List threat assessments.

IUCN Red List assessments have been widely used as the standard for evaluating the risk of extinction for species worldwide. However, the conventional method of doing so is not the only one detailed in the IUCN guidelines. A method using ecological niche modeling (ENM) is detailed in Chapter 4, along with requirements that must be met to adhere to IUNC guidelines. As a test of this approach, the ENM method is applied to the Red List threat assessment of Plerandra elegantissima, a member of the Melanesian Schefflera clade, for which an assessment using the conventional method is already available. The two methods were compared, exploring the advantages and pitfalls of each approach. Both methods resulted in the same threat category for P. elegantissima as Endangered (EN), but with different values underpinning this result. However, the niche modeling method has the added benefit of providing ecological information that can potentially be used to find additional subpopulations of the plant, and can be used to help guide future fieldwork and inform conservation planning for this species. The potential of this method for the entire flora of New Caledonia is also discussed.

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