THE AFRICAN DICHAPETALACEAE a Taxonomical Revision
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582.756.2:581.4/.5+581.9(6) MEDEDELINGEN LANDBOUWHOGESCHOOL WAGENINGEN • NEDERLAND • 73-13 (1973) THE AFRICAN DICHAPETALACEAE A taxonomical revision This first instalment contains the treatment of the species a-b in Dichapetalum Aprovisional key tothe continental African species isadded F. J. BRETELER Department of Plant Taxonomy andPlant Geography, Agricultural University, Wageningen, The Netherlands (Received28-V- l973 ) Dateo fpublicatio n9 Octobe r 1973 H. VEENMAN & ZONEN B.V.- WAGENINGE N -197 3 ^362 Mededelingen Landbouwhogeschool Wageningen 73-13 (1973) (Communications Agricultural University) is also published as a thesis CONTENTS Introduction 1 General part 3 History of the genus 3 Geographical distribution and ecology 3 Systematic position ofth e Dichapetalaceae 5 Morphology 6 Habit and growth 6 Stems and branches 12 Stipules 18 Leaves 20 Indumentum 21 Inflorescences 21 Flowers 24 Fruits and seeds 27 Seedlings 29 Pollen morphology 32 Cytology 33 Flower biology 33 Anatomy 35 Phytochemistry 36 Taxonomiepar t 37 Description ofth e genus Dichapetalum 37 Sectional arrangement 38 Typification and citation of specimens 38 Alphabetical treatment ofth e species and synonyms 39 Summary (English) 113 Summary (Dutch) 114 Acknowledgements 115 References 117 Index of names 122 INTRODUCTION In 1919E . DE WILDEMAN published his 'Notes sur les espèces africaines du genre Dichapetalum Thou.'. In an introduction to this article he made some critical remarks about ENGLER'S 'incomplete and artificial' classification of the African species (1912-a) and noted: 'Le travail de revision, qui devient néces saire, ne peut être entrepris quepa r un monographe qui aura sous la main tous les originaux dispersés dans lesdiver s herbiers'. ENGLER and his collaborators KRAUSE and RUHLAND have described more than one third of the African species, mainly based on material of German collectors. Thus it is evident that the destruction of the African herbarium at Berlin during the last world war caused a great obstacle to future revisions of the genus. HAUMAN (1955: 341) went as far to remark, that a revision as DE WILDEMAN intended, would notb epossibl e anymore. Nevertheless, the present author has undertaken such a revision and this paper forms its first instalment. Thetype-proble m proved to be less insuperable than was estimated. The majority of the types concerned, especially those of ZENKER, are duplicated in several herbaria. Only those in the LEDERMANN col lection from Cameroun, on which 10 species arebased , could have posed serious problems as no duplicates had been distributed. Fortunately, however, frag ments of the LEDERMANN and of other types were found in the British Museum. They had been acquired by Mr. EXELL during a visit to Berlin in the course of preparing his account of the Angolese species (1927). Although these fragments are often very poor, they proved to be extremely useful in the interpretation of ENGLER'S often rather inaccurate descriptions. As a result only in a few, rather clear cutcase s neotypes have tob e designated. The present revision wasinitiate d in 1961 during botanical exploration in the former French Cameroun. The author having serious problems in identifying Dichapetalum specimens came across KEAY'S revision (1958) of the West African species and as a consequence of his remark on the taxonomy of this difficult genus, it was decided to revise the African representatives. Special attention wasgive n to this family during further exploration. Spending a year at Wageningen, literature of the Dichapetalaceae was col lected and studied. The Paris herbarium where the rich collections of KLAINE and LE TESTU from Gabon are conserved, was visited. This work wasinterrupte d by a three years' stay at Merida, Venezuela, but at the end of 1966th e investigation was taken up again. The herbaria of Brussels, Paris, Kew, London, and Oxford were visited, most of them on two or more occasions, and during three separate trips to Africa field exploration could be continued. In 1968 collecting was carried out in Liberia, Ivory Coast, Cameroun, and Gabon. In 1970 Cameroun and Gabon were revisited. During both visits to Cameroun the author collected together with J. J. Boswh o stayed at Kribi at Meded. Landbouwhogeschool Wageningen 73-13 (1973) 1 the time. Togo was explored in 1971 and once more a short visit was paid to Cameroun where he collected together with A. J. M. LEEUWENBERG. This fieldwork as well as the continuous attention paid to this family in bo tanical exploration by other collectors, as J. J. Bos, J. J. F. E. & W. J. J. O. DE WILDE, J. JANSEN, and A.J . M. LEEUWENBERG, added considerably to the present knowledge of the family. More specifically this regards morphology and in- traspecific variation and even stronger geographical distribution, ecology, and habit and growth of the species. As regards this revision, preference was given to publication in instalments. As it was not possible to make a satisfactory division of the genus Dichapetalum on systematical or geographical grounds, the chosen arrangement is not a natu ral one, and though somewhat unusual very practical: th e alphabet. All specific names, whether beingvalidl y published or not, aretreate d in alphabetical order. As HAUMAN(1955 : 340)noted , the species of Dichapetalum are rather uniform in their morphology, not only in their vegetative aspects, but in their generative aspects as well, showing rather few sound differential characters. For that reason it is rather astonishing to note the number of species that have been described. An explanation may be found in the enormous variability in habit, leafshape and leafsize, indumentum, inflorescence, flower dimensions, and even fruit shape and fruit indumentum of the species. It has taken considerable time of critical investigation of numerous specimens before it could be established, that wide differences do indeed exist within one species and that commonly accepted differential characters are quite useless even for infraspecific delimi tation. More detailed information regarding thisvariatio n isgive n inth e chapter on morphology. As a result only about 90 species out of a total of over 220 described can be maintained for Africa. To return once more to DE WILDEMAN, it is illustrative to note, that out of the 21 new species proposed by him in 1919, the present author can uphold but a single one. Meded. Landbouwhogeschool Wageningen 73-13 (1973) GENERAL PART HISTORY OF THE GENUS In 1806 Du PETIT THOUARS described the genus Dichapetalum, basing it on a specimen from Madagascar, but he made no combination for the species intended as a base for thegenus . This wasdon e by POIRET (1812) and he named it D. madagascariense. ROEMER & SCHULTES (1819), overlooking POIRET'S combination, named thetyp e species D. thouarsianum. For a long period the synonym Chailletia DC. (1811) has been used for the genus and more than 30 African species have been described in it. BÂILLON (1874) was the first author who gave priority to the name Dichapetalum and from 1895 onalmos t allne w species were described in Dichapetalum. With theer ao f extensive exploration of Central Africa, especially by German explorers, the great production of specific names started, mainly in Berlin, and to a lesser extent, in Brussels and Paris. ENGLER and his collaborators KRAUSE and RUHLAND are the authors of a hundred names, DE WILDEMAN, partly in collaboration with TH. DURAND is responsible for thirty names, and PELLEGRIN for eleven. Later (1927), EXELL described some newspecie s from Angola. Inal l over 220 specific names have been published forAfric a alone. PELLEGRIN (1913) was the first author to work critically inth eAfrica n species, but hiswor k wasoverlooked , at least not taken into account, by most authors. Besides some revisional work for regional floras (e.g. Flore du Congo, Flore de Madagascar) no comprehensive critical study has been published hitherto on the African species. The American representatives have recently been revised by PRANCE (1972), and theAsiati c species by LEENHOUTS (1956-1972). GEOGRAPHICAL DISTRIBUTION AND ECOLOGY In Africa the main centre of distribution of Dichapetalum is Central Africa, comprising Cameroun, Gabon, Equatorial Guinea, Congo, Zaire, Central African Republic andth enorther n part of Angola. Over 60specie s occur within this area, ofwhic h 40ar eendemic , often with a very limited distribution. Future exploration is expected, however, to reveal considerable extension of these small distribution areas. In the area of the Flora of West Tropical Africa (2nd ed.), i.e. excepting Western Cameroun, 28 species occur of which only 7 are confined to this area, while theremainin g 21 occur in Central Africa as well.D. bocageanum is endemic on Sao Tomé and Principe. Central- and East Africa (Uganda, Kenya, Tanzania, and Moçambique) have only four species in common, except D. ugandense which occurs mainly in Meded. Landbouwhogeschool Wageningen 73-13 (1973) 3 the border region between Zaïre and Uganda, and D. angolensewhic h has only been collected in western Uganda. The East African species occupy a second centre of distribution mainly restricted to the coastal area of Kenya, Tanzania, and Moçambique, where 13 species are found of which at least 8 species are confined to this area, some of them (D. braunii, D. edule, D. macrocarpum) even to a very small part of it in S.E. Tanzania and N.E. Moçambique. From this small area the present East African species, at least those which are entirely confined to this second centre of distribution, may have migrated intw o opposite directions: D. arenariuman d D. eickii to the north, and D. barbosae and D. deflexum to the south, while some species, like D. mossambicense,hav e spread in both directions. Only two species are confined to South Tropical Africa :D. cymosum and D. rhodesicum, of which the former extends into the northern part of the Republic of South Africa.