Rafflesiaceae

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Rafflesiaceae

Rafflesia kerrii flower

Scientific classification

Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Malpighiales
Family:	Rafflesiaceae Dum.

Genera

See text.

Illustration of a Rafflesiaceae species from Der Bau und die Eigenschaften der Pflanzen (1913).

Rafflesiaceae is a family of parasitic plants found in east and southeast Asia, including Rafflesia arnoldii, the plant with the largest flower of all plants. The plants are endoparasites of vines in the genus Tetrastigma (Vitaceae) and lack stems, leaves, roots, and any photosynthetic tissue. Only the flowers emerge from the roots or lower stems of the host plants.

Rafflesiaceae has been considered an unplaced family in the APG II system, while other authors placed it into the order Rafflesiales together with some other families of parasitic plants. More recent research places the family (in a restricted circumscription) in order Malpighiales (Barkman et al., 2004), and also does not consider the other families of the Rafflesiales order as related anymore (Nickrent et al., 2004).

The family sensu lato has traditionally included 9 genera, which have around 50 species altogether.

Genera

Apodanthes
Bdallophyton
Berlinianche
Cytinus
Mitrastemon
Pilostyles
Rafflesia
Rhizanthes
Sapria

The taxonomic treatment has been varied though, with various authors placing different genera in their own families (Meijer, 1997). More recent taxonomic works treat Rafflesiaceae as a family in the wide sense (Rafflesiaceae sensu lato) with four tribes first recognised by Harms (1935), and supported by Takhtajan et al. (1985).

Tribes

Rafflesieae: Rafflesia, Rhizanthes, Sapria
Apodantheae: Apodanthes, Pilosytles
Cytineae: Bdallophyton, Cytinus
Mitrastemeae: Mitrastema

[edit] Relationships

Recent research shows that Rafflesiaceae as traditionally circumscribed is polyphyletic. Rafflesiaceae is restricted to the genera Rafflesia, Rhizanthes, and Sapria. The other genera have been moved to families Apodanthaceae (Apodanthes, Berlinianche, Pilostyles), Cytinaceae (Bdallophyton, Cytinus), and Mitrastemonaceae (Mitrastema) (Nickrent et al., 2004), which follows the concept of Harms and Takhtajan et al.

New hypothesis of Rafflesiaceae derived from within Euphorbiaceae. Rafflesiaceae in red, Euphorbiaceae in black (redrawn from Davis et al., 2007).

Early work on higher-level relationships was able to place Rafflesiaceae (in the strict sense) within the order Malpighiales, but was not able to resolve the closest ancestor within the order^[1]. A more recent phylogenetic analysis found strong support for Rafflesiaceae being derived from within Euphorbiaceae, which is surprising as members of that family typically have very small flowers.^[2] According to their analysis, the rate of flower size evolution was more or less constant throughout the family except at the origin of Rafflesiaceae - a period of about 46 million years between when the group split from the higher Euphorbiaceae, and when the existing Rafflesiaceae split from each other - where the flowers rapidly evolved to become much larger before reverting to the slower rate of change. If this hypothesis is confirmed, in order to maintain monophyly of Euphorbiaceae, either the basal clade (represented by Pogonophora, Pera, and Clutia in the tree) will have to be split off as a separate family (and in fact Pera is recognized in the separate family Peraceae in some classifications), or Rafflesiaceae will have to be included in the Euphorbiaceae.

[edit] References

^ (January 20, 2004) "Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world's largest flower". PNAS 101 (3): 787-792.
^ Davis C. C., et al. Science, doi: 10.1126/science.1135260 (2007).

Barkman, T.J., S.-H. Lim, K. Mat Salleh and J. Nais. 2004. Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world's largest flower. Proceedings of the National Academy of Sciences of USA 101:787–792.
Charles C. Davis, Maribeth Latvis, Daniel L. Nickrent, Kenneth J. Wurdack, David A. Baum. 2007. Floral gigantism in Rafflesiaceae. Science Express, published online January 11, 2007 (online abstract here).
Meijer, W. 1997. Rafflesiaceae, in Flora Malesiana I, 13: 1–42.
Nickrent, D.L., A. Blarer, Y.-L. Qiu, R. Vidal-Russell and F.E. Anderson. 2004. Phylogenetic inference in Rafflesiales: the influence of rate heterogeneity and horizontal gene transfer. BMC Evolutionary Biology 4:40 (HTML abstract PDF fulltext).