Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Lowell E. Urbatsch

Abstract

The current project undertakes the first molecular-based phylogenetic study of subfamily Epidendroideae (Orchidaceae). Approximately 1,200 nucleotide bases (from the 3$\sp\prime$ half of the ndhF chloroplast gene) for 34 orchid taxa, and a lilioid monocot, Clivia miniata, (Amaryllidaceae) were subjected to phylogenetic analysis using parsimony methods. Oryza sativa (Poaceae), a nonlilioid monocot was designated as outgroup. Using unweighted ndhF sequences, the strict consensus cladogram of 531 most-parsimonious trees supports the hypothesis that the large subfamily Epidendroideae is monophyletic, with Listera (Neottieae) as sister. Although subtribal-level relationships in subfamily Epidendroideae ate well resolved in this analysis, tribal-level relationships are resolved poorly. A set of 13 morphological characters were combined with unweighted ndhF sequences and used in parsimony analyses. Although the addition of these characters brings an increased level of resolution to the intertribal relationships in Epidendroideae, branch support for these relationships is weak. Six taxa in this study exhibit deletions that are not evenly divisible by three which results in extensive sequence frameshifts. This suggests that ndhF may be a pseudogene, in these six taxa. A maximum likelihood analysis was also undertaken to infer phylogenetic relationships for the taxa included in this study. To determine the maximum likelihood tree with the greatest log likelihood, an array of transversion weighing parameters and jumble seeds were used in this analysis. A tree with the greatest log likelihood value ($-$7,473.95) was discovered with a transversion parameter of 1.1. This maximum likelihood tree, suggests that subfamily Epidendroideae is monophyletic with Listera (Neottieae) as sister. Although trees discovered from these two methods of phylogenetic inference are congruent in many respects, topological differences typically occur on branches that define intertribal relationships among the epidendroids. It is hypothesized here that this lack of support is due to a rapid radiation of the epidendroids which coincided with anatomical, morphological, and physiological adaptations that allowed the epidendroids to pioneer xeric epiphytic microhabitats.

Pages

232

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