Phylogenetic analysis of the Aspleniaceae : an assessment of its taxonomy and distribution

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Type
Thesis
Author
Siti Khadijah Rambe
Supervisor
Lum, Shawn K. Y.
Abstract
Aspleniaceae is one of the biggest families of ferns and lycophytes, and comprises about 750 species widely distributed from the tropics to the temperate zone. As a consequence of a large number of species, the family has highly diverse morphological characters. Classification systems consisting of groups sharing the same phenotypic characteristics were limited by the absence of objective criteria for character weighting. Thus, a taxonomic study based on morphological characters might easily lead researchers to diverse opinions, which is partially caused by the differing abilities of the researchers to observe existing characters. In attempt to obtain a phylogenetically accurate taxonomic scheme for the genus, to better assess the evolution of character traits, and to understand the migratory history of the Aspleniaceae, this molecular study was conducted. The phylogeny of combined chloroplast rbcL and trnL-trnF non-coding intergenic regions of the Aspleniaceae was determined using an unpreceded number samples, 147, representing all continents except Antarctica. The current phylogeny revealed that most taxonomic characters that were proposed earlier for defining genera within the family were valid largely at the species level. In addition, the study found that very few characters carry taxonomical significance, and these are of the root and juncture. The jucture, located at the lateral sides of the rachis and which can be extended to the petiole, is formed by the excessive parenchyma cells. Subsequently, this study found that pleisiomorphic and apomorphic character stages of the root and juncture characterized the evolution of three proposed subgenera within Asplenium namely: subgenus Asplenium having pleisiomorphic characters for both root and juncture, subgenus Tarachia with pleisiomorphic characters for the root and apomorphic characters for the juncture, and subgenus Caenopteris having apomorphic characters for both root and junctures. The evolution of root and junctures suggested a differentiation between lithophytic and an epiphytic habitat preferences at the early nodes of Asplenium division. Evolutionary transitions from a lithophytic habit towards an epiphytic habit were supported by the phylogeny. The age of differentiation of the defined subgenera was estimated around 37 Mya which corresponds to the beginning of the reduction of the Boreotropical flora that culminated with the Quaternary glaciations. Both long-term and short-term climate variations as well as the proliferation of flowering plants were hypothesized as a potential trigger of the Asplenium early speciation events.
Date Issued
2010
Call Number
QK524.A7 Sit
Date Submitted
2010