A taxonomic study of the Ebenaceae with special reference to Malesia

The Kbenaceae is a family of woody, mostly tropical plants consisting of about 500 species, some of which produce the ebony of commerce, and a few others produce the edible fruits known as persimmons. About 300 species occur in the Indo-Pacific area, with the greatest concentration, of 150 - 200 species, within the tropical rain forest region known as Malesia, which includes the political units Malaysia, Indonesia and the Philippines.
This study is based primarily on herbarium material of Malesian species but whenever it has been necessary to ignore the Malesian boundary in the interests of acquiring a better understanding of the plants, I have done so. Hence all species in the Inde-Pacific area have been examined, at least casually, but some ia considerable detail. A few critical examples from Africa have also been included.
The last comprehensive monograph on the family was written almost a century ago, by Hiern (1873), when only 262 species were recognised. Hiern's monograph is now completely out of date at species, sectional and generic levels. For Malesia, the standard regional monograph was completed by Bakhuisen in 1941. This work too, is out of date because much more new material has been collected, especially from areas formerly difficult to reach and consequently under-explored.
The present study is divided into four parts. The first part consists of a series of investigations into form and structure within the family, covering carpel and seed morphology, seedling behaviour, pollen morphology, wood anatomy, various features of the epidermis especially trichomes and stomata, and karyotype.
It was found that tho Ebenaceous gynoecium is composed of 2-8 bi-ovulate carpels "fused" to form a multilocular ovary. However, false septa are developed in all except 11 species. These false septa have usually not been recognised for what they are, and for this reason, descriptions of carpol morphology and the use of carpel characters in previous taxonomic treatments of the family have betrayed a considerable amount of confusion which the present research has cleared up.
Pollen morphology and woody anatomy is remarkably constant throughout the family. Chromosome number is very stable. A single euploid series 2n m 30, 60, 90 applies right through the family.
Epidermal structures are, on the other hand, more variable than might have been expected, e.g. there are simple, branched, tufted, glandular and peltate trichomes; stomata may bo anomocytic or have subsidary cells of various forms.
Seedling behaviour during germination is variable, some species being neither hypogeal nor epigeal and have to be described by considering the behaviour of the hypecotyl and tho cotylodens separately.
The second part is an investigation into the limits of the family. This consists of a series of critical comparisons between Kbenaseae and the families Sapetaceae, Sarcospermataceae, Styracaceae, Symplocaseae and Liasoearpaceae. A large number of characters were examined, in the process of which several important points emerged.
Carpel structure has been consistantly misinterpreted especially in the system of Engler (1964). Contrary to the claim that the Sapotaceous ovary is completely partitioned into lecules, by which it differs from the partially "open" condition in Kbenaseae, Styracaceae and Symplocaseae it was found that the lecules in every Sapetaceous ovary examined, are in connection with each other by means of a compitum of varying size. In fact, all the six families involved in this survey are eu-syncarpous (Carr & Carr 1961).
Trichome characters are unreliable as markers for the various families. Popular association of branched hairs with Sapetaceae and simple hairs with Ebenaceae and Symplocaceae turn out to be oversimplifications of the truth.
In previously published definitions of these six families, the boundaries between them appear to be funny. It was found that much fussiness merely reflects bad choice of characters and misunderstanding of certain structures and of their extent of variation. The families are in fact either very sharply defined from each other or not clearly definable at all. Sarcospermataceae ia a bad family, quite indistinct from Sapetaceae. All the other families are sharply defined from each other by several to many characters, and there are no problems of intermediate taxa. Lissocarpaceae, sometimes thought to be intermediate between Ebenaceae and Styracaceae, is a distinct family but probably tho meet closely related to Ebenaceae of all the families considered. Sapetaceae usually thought of as the closest family to Ebenaceae is in fact most different. The naturalness of the Order Ebenales is put in doubt.
In the third part, Bakhuisen's classification of Malesian Ebenaceae (actually Dioapyres since this is the only genus in Malesia), ie put to the test using a taximetrlc procedure of character analysis. The results support the maintainance of Hierniodendron and Brachycylix as infra-generic taxa worthy of recognition. Support for the other sub-genera and sections was feeble to nil. The genus Dioapyres is probably best considered to consist of one very large variable section (Sect. Dioapyres) and a small number of little ones.
Problems of species delimitation do not loom very large in this study, but in the fourth part, three species-complexes were analysed for morphological variation over their entire range. In one of these analyses, involving Dioapyres sylvatica, D. ehreticides, D.hermaphredies and D.fasciculesa, an interesting pattern of allopatry emerged, which suggested that some of these taxa could be regarded as geographical subspecies. The other two analyses were carried out on D.kaki, D.lotus and their relatives. These species produce edible persimmons. Problems of their origin and spread are consequently of wider than taxonoaic interest, but the taxonomic approach adopted here serves to sharply outline various hypothoses that ethers may be able to test by cytotaxonomic and other means. It is suggested that D.kaki originated from D.roxburghii, which is now found wild in the forests of Assan, Burma, Thailand, Yunnan and Indo China. The controversial problem of the role of man in the distribution of D.lotus is reviewed and summarised.