Jon L.R. Every
Royal Botanic Gardens, Kew, UK.
Holoparasitic, achlorophyllus, rootless with a filamentous endophyte in roots of host, 5-8 cm high. Leaves opposite decussate, whorled around the base of the solitary flower, reduced or absent, scale-like, coriaceous, apex obtuse. Flowers terminal, solitary, erect, nectaries in axils of upper bracts, actinomorphic, hermaphroditic, protandrous, gamophyllus, cupiliform, calyx of 4(-10) sepals, imbricate, truncate or a more or less 4-lobed collar around pistil, persistent; petals absent; stamens fused to form a caducous tube (androphore), crowned by a fertile zone of pollen-bearing locules that has an opening at top; anthers numerous and in several series, above each other, opening by slits or pores; ovary superior, syncarpous, sessile, ovules numerous, carpels (4-)9-15(-20), 1-locular; style 1 terminal, short, very thick, stigma conic. Fruit a somewhat woody capsule opening by a transverse slit or indehiscent berries; seeds numerous, small, with a hard testa, exotesta juicy or papery surrounded by a whitish, slimy pulp.
Notes on delimitation
- Mitrastemon Makino was thought to belong to the Rafflesiaceae alongside other Neotropical genera such as Cytinus L. (treated here in the Cytinaceae), Psilostylus Guill. plus the endemic Adodanthes Poit. and Bdallophyton Solms. Following the interpretation of the mitochondrial DNA sequences of the putative Rafflesiaceae it became apparent that Mitrastemon is in fact only distantly related to the Rafflesiaceae sensu lato and is actually placed as sister to the cranberry (Vaccinium L.) (Barkman 2003).
- Originally described as Mitrastemma (the name was changed by Makino when he raised the genus to family rank), a name by which it is sometimes still referred.
Distribution in the Neotropics
Mitrastemon has two species one of which is represented in the Neotropics:
- Mitrastemon matudae Yamam. occurs from Mexico to Guatemala and into Northwestern Colombia.
Distinguishing characters (always present)
- Lack of green parts i.e. achlorophyllous.
- Bisexual flowers.
- Collar shaped, +/- 4-merous perianth tube.
- Connate stamens (that split as the pistil develops from below).
- Superior, unilocular ovary.
Other important characters
- Often forming dense colonies.
- Generally parasitic on members of the Fagaceae (e.g. Quercus L.).
- Flowers are medium-sized (2-2.5 cm in diametre) and white.
- Leaves are reduced to dark brown scales.
Key differences from similar families
- Rafflesiaceae do NOT have bisexual flowers, nor a superior ovary.
- Cytiniaceae do NOT have bisexual, solitary flowers.
Number of genera
- Monogeneric with one species in the Neotropics.
- From the Latin mitra and stema referring to the manner in which the stamens are connate into a turban-shaped tube.
- Also recorded to have found suitable hosts outside the Fagales with members of Aquifoliacae, Compositae, Elaeocarpaceae, Juglandaceae and Myrtaceae providing the nutrient source for Mitrastemon (Nickrent 2004).
Barkman, T. J., Lim, S-H., Salleh, K. M. & Nais, J. 2004. Mitochondrial DNA sequences reveal the photosynthetic relatives of Rafflesia, the world's largest flower. PNAS 101(3): 787-792.
Davies, C.C. 2008. Floral Evolution: Dramatic size change was recent and rapid in the world's largest flowers. Current Biology 18(23): 1102-1104.
Heywood, V.H. 2007. Mitrastemonaceae. In: Heywood, V.H., R.K. Brummitt, A. Culham & O. Seberg (eds). Flowering plant families of the world. pp.215-216. Kew: Royal Botanic Gardens, Kew.
Matuda, E. 1947. On the genus Mitrastemon. Bulletin of the Torrey Botanical Club 74(2): 133-141.
Meijer, W. 1933. Rafflesiaceae. In: Kubitzki, K. (ed.). Families and genera of vascular plants. Volume 2. Flowering plants. Dicotyledons. pp557-563. Springer-Verlag, Berlin.
Nickrent, D.L., Blarer, A.,Qiu, Y.L. Romina, Vidal-Russell, R. & Anderson, F.E. 2004. Phylogenetic inference in Rafflesiales: the influence of rate heterogeneity and horizontal gene transfer, BMC Evolutionary 4: 40.
Standley, P. C. & Steyermark, J. A. 1946. Flora of Guatemala. Fieldiana, Botany 24(4): 101-104.
How to cite
Every, J.L.R. (2009). Neotropical Mitrastemonaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Mitrastemonaceae.htm.