Malmea

Abstract: Results are presented of research on a family of flowering plants, the Annonaceae, species of which are found in tropical rainforest across the world. The project focussed on one group of species, the genus Cremastosperma, which is found in the South and Central American tropics. A taxonomic revision of Cremastosperma was made. Most of the species of Cremastosperma are found along the foothills of the Andes. Twenty-nine species were recognised, 13 of which were new to science. They are often narrow endemics, found only in areas such as the valleys of the Magdalena River in Colombia (e.g. C. magdalenae), and Maranon in Peru (e.g. C. bullatum). A resolved phylogeny can be used to infer the ancestral distributions of a clade, and possible factors behind its radiation. DNA sequences were compared in order to reconstruct the phylogeny of 19 of the 29 species of Cremastosperma. A number of clades were revealed. These included species distributed either west or east of the Andes mountain chain, providing further evidence to suggest the importance of the Andean orogeny as a vicariance event in the history of the evolution of Cremastosperma. Many other groups of plants share this ‘Andean-centred’ distribution, and the rising of the Andean mountain chain has thus been hypothesised to have caused the origin of a large proportion of the high biodiversity of the New World tropics. DNA sequences were used to reconstruct the relationships between species of four Andean-centred genera of Annonaceae, Cremastosperma, Klarobelia, Malmea and Mosannona, and to estimate how long ago those species shared common ancestors. The conclusion was drawn that the Andean-centred distribution patterns as observed are not the arbitrary result of the definition of poly-or paraphyletic groups. The timing of species diversifications in these groups was shown to coincide with the rise of the northern Andes, within the last 20-30 million years. Further research compared the timing of diversifications in Cremastosperma and Mosannona with those in two more widely distributed and species rich genera, Duguetia and Guatteria. The effects of taxon and character sampling on date estimates in these genera were assessed and compared. Higher sampling of crown group taxa of the species-rich genus Guatteria resulted in significantly older age estimations, representing a potentially serious bias in a widely used molecular dating method (nonparametric rate-smoothing). Molecular dating techniques should be assessed for sensitivity to levels of taxon sampling under differing conditions. Finally, an ancient paralogue of the widely used chloroplast marker trnL-F was discovered, the origin of which was inferred to have taken place in a common ancestor of the Annonaceae. The paralogue discovered evolves at a faster rate and appears to have complementary phylogenetic signal. It may be a useful phylogenetic marker. Although the exon appears to be intact, some intron sequences show signs of disruption of the secondary structure which is otherwise conserved across land plants. Function may thus have been lost. Future research should attempt to determine both the whereabouts and origin of both copies of trnL-F in the Annonaceae genome.

Abstract: Cluster analysis is used to reveal patterns of macromorphological variation in a species complex of Malmea (Annonaceae) distributed in eastern Mexico, Guatemala, Belize, and Honduras. Of 53 characters, 24 are important for the clustering of 238 herbarium specimens into 12 clusters. No cluster is exclusively specified by any character or combination of characters. Neither can any geographical pattern be detected, except for the clustering of specimens from Los Tuxtlas Tropical Biological Station, Veracruz. A new subspecies from this area, M. depressa subsp. abscondita, is described. Malmea gaumeri and M. leiophylla are brought into synonymy with M. depressa. Distribution patterns of Mexican and Central American taxa of Malmea are largely concordant with those of South American taxa, which spread into Cental America after the Pliocene closure of the Isthmus of Panama. A phytogeographical novelty is presented, however, as the distribution of M. depressa subsp. abscondita within the Sierra de los Tuxtlas shows an hitherto unknown pattern: the new subspecies is distributed only on the northeastern slopes of this mountain range, and is geographically separated from M. depressa subsp. depressa, which occurs only on the southwestern slopes.

Abstract: For better understanding of intrafamilial relations of Annonaceae, number and morphology of chromosomes were studied. Additional informations of 16 collections and previous reports were considered. An ascending series of n=7→8 was available in Annona spp., Malmea Tribe, Cleistopholis sp., Fusaea Tribe, Uvaria spp. Number n=9 was common in Polyalthia, Miliusa, Artabotrys (8→9) and Asimina. In n=7→8 lines, Uvaria and Desmos had primitive chromosome morphology. In n=8→9 lines Artabotrys showed primitive karyotypes, Miliusa and Asimina the most advanced ones.