Friday, January 12, 2007
Rafflesiaceae: Family found for gigantic flowers (+ Video)
The 200-year-old mystery of where some of the world's largest flowers sit in the botanical family tree has finally been solved by scientists.
To their surprise, the plants, which have up to 1m-wide (3ft), blood-red, rotten-flesh stinking flowers, belong to a group bearing tiny blooms.
The Rafflesiaceae were tricky to place because of their unusual features, the team reports in the journal Science.
Such traits include the fact that they are rootless, leafless and stemless.
...And the strange plants, which can be found growing on the jungle floor in southeast Asia, are also parasitic. Eschewing the process of photosynthesis, the Rafflesiaceae bed down in the tissue of the tropical grape vine, feasting upon the nutrients it provides.
...Charles Davis (lab), assistant professor of organismic and evolutionary biology at Harvard University and lead author of the Science paper, said: "These plants are so strange - almost extra-terrestrial - wherever they were placed [within the family tree] there would be a lot of explaining to do."
Continued at "Family found for gigantic flowers" (BBC Science News UK)
Based on the paper:
Floral Gigantism in Rafflesiaceae
Charles C. Davis et al.
Published Online January 11, 2007
Science DOI: 10.1126/science.1135260
Species of Rafflesiaceae possess the world's largest flowers (up to 1 m in diameter), yet their precise evolutionary relationships have been elusive, hindering our understanding of the evolution of their extraordinary reproductive morphology. We present results of phylogenetic analyses of mitochondrial, nuclear, and plastid data showing that Rafflesiaceae are derived from within Euphorbiaceae, the spurge family. Most euphorbs produce minute flowers, suggesting that the enormous flowers of Rafflesiaceae evolved from ancestors with tiny flowers. Given the inferred phylogeny, we estimate that there was a ca. 73-fold increase in flower diameter on the stem lineage of Rafflesiaceae, making this one of the most dramatic cases of size evolution reported for eukaryotes.
Video of Rafflesia 'in the wild':
Also see the 2004 open access/free paper from Proceedings of the National Academy of Sciences (PNAS):
Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world's largest flower
Todd J. Barkman et al.
PNAS | January 20, 2004 | vol. 101 | no. 3 | 787-792
All parasites are thought to have evolved from free-living ancestors. However, the ancestral conditions facilitating the shift to parasitism are unclear, particularly in plants because the phylogenetic position of many parasites is unknown. This is especially true for Rafflesia, an endophytic holoparasite that produces the largest flowers in the world and has defied confident phylogenetic placement since its discovery over 180 years ago. Here we present results of a phylogenetic analysis of 95 species of seed plants designed to infer the position of Rafflesia in an evolutionary context using the mitochondrial gene matR (1,806 aligned base pairs). Overall, the estimated phylogenetic tree is highly congruent with independent analyses and provides a strongly supported placement of Rafflesia with the order Malpighiales, which includes poinsettias, violets, and passionflowers. Furthermore, the phylogenetic placement of Mitrastema, another enigmatic, holoparasitic angiosperm with the order Ericales (which includes blueberries and persimmons), was obtained with these data. Although traditionally classified together, Rafflesia and Mitrastema are only distantly related, implying that their endoparasitic habits result from convergent evolution. Our results indicate that the previous significant difficulties associated with phylogenetic placement of holoparasitic plants may be overcome by using mitochondrial DNA so that a broader understanding of the origins and evolution of parasitism may emerge.
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