Phylogenetic analysis in the order Malvales has led to the suggestion that the core Malvales (Sterculiaceae, Tiliaceae, Bombacaceae, and Malvaceae) should be considered an enlarged family, Malvaceae s.l., and that nine subfamilies be recognized (Bayer et al. 1999; Alverson et al 1999). One of these subfamilies, the Sterculioideae, is currently under investigation by Dr Peter Wilkie of RBGE.
The Sterculioideae share several characters including apetalous flowers, ± petaloid sepals, secondary apocarpy, mostly unisexual flowers and the presence of sheath cells. The subfamily is composed of 13 genera. Several genera, such as Sterculia and Hildegardia, are pan-tropical while others have a more or less restricted distribution. The genera Scaphium, Heritiera, Firmiana, Pterocymbium and Pterygota are predominantly found in South East Asia, Acropogon in New Caledonia, Brachychiton, Franciscodendron and Argyrodendron in Australia, and Cola and Octolobus in Africa.
A New Phylogeny of the Sterculioideae
A recent analysis of ndhF nucleotide sequences representing at least one exemplar of each genus in the Sterculioideae, strongly supports the monophyly of the group (Wilkie et al 2006). Within the Sterculioideae clade four major clades are recognized with good bootstrap support but relationships among them are not resolved. This analysis suggests the recognition of Argyrodendron as separate from Heritiera, supports Acropogon as separate from Sterculia, and Tarrietia as part of Heritiera. The current circumscriptions of Hildegardia and Firmiana are not supported and the relationship between Scaphium and Pterocymbium needs further investigation.
A Phylogeny of Scaphium
A paper is currently in preparation which investigates the close relationship between the genera Scaphium and Pterocymbium. Phylogenetic reconstructions have been undertaken for a range of nuclear and chloroplast regions (ITS, trnL-trnF, trnH-psbA, and trnS-trnG) and with greater sampling of both genera. Provisional analyses support two possible schemes of relationships: 1. a monophyletic Scaphium sister to a monophyletic Pterocymbium; 2. a paraphyletic Scaphium with Pterocymbium nested within it.
Given the moderate to strong support from the chloroplast data for a monophyletic Scaphium, the weak support for paraphyly from ITS data and the unique morphological characters which are potential synapomorphies for each genus, both genera are being maintained as separate until more conclusive research is available.
A Revision of the Genus Scaphium
As part of the research programme on Sterculioideae a revision of the genus Scaphium is being produced. Locally known as Kembang semangkok, the seed is exported in dry form for medicine to India and China and the jelly produced when a little water is added drunk as a febrifuge and used for coughs, asthma and dysentery. The genus is composed of tropical trees and is an important component of the lowland forests of Burma, Indo China, Thailand, Peninsular Malaysia, Sumatra and Borneo. Species delimitation in Scaphium has been problematic and has led to confusion in identification of species. It was last revised by Kostermans (1953) who recognized four species. Since then five new species have been published and 13 species names are now attributed to the genus by the International Plant Names Index (IPNI). A revision of the genus is therefore timely.
A Revision of the Genus Firmiana
Based on the subfamily phylogeny of the Sterculioideae (Wilkie et al 2006), Ganesan Santhana from the National Parks Board Singapore and Peter Wilkie from RBGE are currently undertaking a revision of the genus Firmiana. Provisional results suggest a re-circumscription of the genus may be necessary.
Tree Flora of Sabah and Sarawak
As part of a Forestry Research Institute Malaysia (FRIM), Peter Wilkie is producing an account of the Sterculiaceae for the Tree Flora of Sabah and Sarawak. As other families in the core Malvales have already been published in previous volumes of the Tree Flora of Sabah and Sarawak an account of the traditional family Sterculiaceae is being produced for volume seven. This account, although covering the family Sterculiaceae in the traditional sense, will cross reference all genera to the new subfamily classification of Bayer et al (1999) and covers 11 genera, 47 species and five varieties.
For further information contact: Peter Wilkie
Alverson, W. S., Whitlock, B. A., Nyffeler, R., Bayer, C. & Baum, D. A. (1999). Phylogeny of the core Malvales: Evidence from ndhF sequence data. Amer. J. Bot. 86(10): 1474-1486.
Bayer, C., Fay, M. F., De Bruijn, P. Y., Savolainen, V., Morton, C. M., Kubitzki, K., Alverson, W. S. & Chase, M. W. (1999). Support for an expanded family concept of Malvaceae within a recircumscribed order Malvales: a combined analysis of plastid atpB and rbcL DNA sequences. Bot. J. Linnean Soc. 129(4): 267-303.
Kostermans, A. J. G. H. (1953). The genera Scaphium Schott and Endl. and Hildegardia Schott and Endl. (Sterculiaceae). Journal of Science Research Indonesia 2(1): 13-23.
Wilkie, P., Clark, A., Pennington, R.T., Cheek, P., Bayer, C., & Wilcock, C.C. (2006) Phylogenetic Relationships within the Subfamily Sterculioideae (Malvaceae/Sterculiaceae-Sterculieae). Using the Chloroplast Gene ndhF. Systematic Botany 31:160-170.