Abstract
The Neotropics (Mexico to South Brazil) contains c. 30% of the world's plant diversity, but the origin of this diversity remains unclear. Several recent studies have suggested that a substantial portion of this diversity has resulted from the dispersal of taxa into that region. However, more data are needed to
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substantiate this claim. Guatteria (Annonaceae) is with c. 290 species the third largest genus of Neotropical trees. Its widespread distribution and frequent occurrence makes the genus an excellent model taxon to study diversification patterns. This dissertation reconstructed the evolutionary history of Guatteria and inferred three major events in the history of this genus: 1) A migration across the ocean from Central into South America before the closing of the Isthmus of Panama; 2) a major diversification of the lineage within South America; and 3) several migrations of South American lineages back into Central America via the closed Panamanian land bridge. Therefore, most of the species of Guatteria resulted from a major radiation that followed its dispersal into South America over 6 million years ago. This study provides further evidence that migration into the Neotropics was an important factor in the historical assembly of its biodiversity.
Next to this, the accepted classification of the species within Guatteria as well as the relationship between Guatteria and its small satellite genera (Guatteriopsis, Guatteriella and Heteropetalum) was investigated. Current classification of Guatteria is based on morphology and species are often difficult to tell apart. Because of this morphological complexity researchers have been reluctant to study these plants. Therefore, the last thorough study of this genus as a whole dates back to 1939. In this dissertation, an evolutionary tree containing c. 40% of the species of Guatteria was constructed. This was done on the basis of chloroplast DNA. Unfortunately, clear insight in most of the evolutionary relationships between species was not achieved. Therefore, a completely new classification of Guatteria would be premature. However, it is clear that the largest part of the currently accepted classification should be abandoned. Notwithstanding this, conclusions could be drawn on the morphological evolution of the genus. Furthermore, the closest relative of Guatteria could not be determined with certainty. This knowledge is necessary in order to understand the origin of the genus. A morphological nightmare for taxonomists in the past decades proves to some extent to be a mystery for molecular biologists, even today.
The Central American species of Guatteria are in general easier to tell apart than the South American representatives. In order to study these species, field work in Costa Rica and Panama was carried out. During this fieldwork five new species of Guatteria were discovered and named. These species were studied together with all the already known Central American species of Guatteria and the resulting Flora treatment is included in this dissertation. The descriptions of the species, accompanied by photographs, can be used by specialists and non-specialists to identify herbarium material of Central American Guatteria's.
Finally, the use of herbarium specimens in this molecular phylogenetic study was evaluated.
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