Revealing Relationships

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Science  06 Feb 2004:
Vol. 303, Issue 5659, pp. 731
DOI: 10.1126/science.303.5659.731b

Rafflesia, a genus of 16 species of parasitic plants inhabiting the tropical rainforests of Southeast Asia, harbors the world's largest flower—a giant 1 m across that attracts pollinating flies with its odor of rotting carrion. Despite its iconic status, Rafflesia's evolutionary history has remained uncertain; unraveling the phylogenetic relationships of parasitic plants is often tricky because many morphological and genetic features are lost or much modified in the transition to the parasitic life-style.

Barkman et al. used a comparison of mitochondrial DNA (mtDNA) sequences to place Rafflesia in its phylogenetic context among the angiosperms. Plant mtDNA tends to have lower mutation rates than other components of the plant genome and hence can yield more reliable phylogenies. Their approach places Rafflesia close to the Malpighiales, an order of flowering plants that includes the passion flowers—confirming at last the relationship first noted by Robert Brown (of Brownian motion) in 1822. Such analyses, applied to further groups of parasitic plants, will help to reveal the evolutionary pathways by which plants can switch from photosynthetic to parasitic mode. — AMS

Proc. Natl. Acad. Sci. U.S.A. 101, 787 (2004).

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