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Record: oai:ARNO:524469

AuthorC.F. van Beusekom
TitleA revision of the Malesian and Ceylonese species of the genus Gaertnera Lamk. (Rubiaceae)
JournalBlumea - Biodiversity, Evolution and Biogeography of Plants
AbstractIn chapter I the systematical position of Gaertnera is discussed and arguments are given for its arrangement in the Rubiaceae-Psychotrieae as well as the characters by which it can be distinguished from Psychotria. In chapter 2, section a, the morphology is explained of the various types of inflorescence and their derivation. It appeared that in most species the inflorescence is fairly characteristic. In G. vaginans, however, it gradingly varies from widely paniculate to condensed and from very profuse to depauperate. Section b offers new interesting data on the three types of flowers, bisexual and heterostylic, bisexual and homostylic, and unisexual-dioecious. Each individual plant carries only one kind of flowers. These kinds of flowers have within the genus also a distinct geographical significance: bisexual-heterodistylic flowers are peculiar to all Ceylonese and African species, possibly also to the Madagascan ones, whereas all Indo-Malesian species are dioecious, G. vaginans excepted. G. vaginans possesses in Africa and Ceylon bisexual-heterodistylic flowers, in Indo-Malesia dioecious flowers, and in some local Bornean populations bisexual flowers without heterodistylism. Section b contains further an evaluation of distinctive characters of other floral parts. Section c, on fruit and seed, shows the great uniformity of these in all species, except those of the Madagascan area. Sections d and e deal with the bracts and stipular sheath and their structure. Section f is devoted to the leaf, the size of which is hardly of specific value, but the indument does. On poor sandy soils and on ridges and summits leaves appear smaller and thicker.
Chapter 3 embraces a discussion of the distribution; one species, G. vaginans, is covering the entire range of the genus, from West Africa to Borneo, included Madagascar. The greatest species density is found in Madagascar and the Mascarenes where all species, except G. vaginans, are endemic. Ceylon has 4 endemic species of which two may prove to be races of one. In Malaya and Borneo 7 endemic species occur, whilst G. vaginans covers all this area including also scattered localities in Thailand and Indochina. All Malesian, Ceylonese, and presumably all African species are mutually related and share with the omnipresent G. vaginans the same kind of fruit. Most of the Madagascan species, however, are different in this respect and this leads to the view that the Madagascan area is probably the primary distributional centre. From this centre G. vaginans emanated which must be the ancestral species of all others outside the Madagascan area. The likeliness of this assumption is derived from the fact that its range is enormous and its plasticity greatest among all other species. The fact that its floral dimorphism from Ceylon westward to Africa is opposed to its dioecism in Indo-Malesia, leads to the view that the former part of the area is more ancient than the latter, and that the proportionally youngest extension of the genus was from Ceylon eastward towards continental Asia and Malesia, in which a secondary centre of speciation was formed.
The special part comprises the taxonomical treatment with a key to and descriptions of 12 species, among which 2 are new ( G. fractiflexa and G. globigera from Borneo). A fairly large number of names has been reduced, 6 to G. oblanceolata, 14 to G. vaginans among which several from continental Asia and one from Africa; they are both rather variable species and in the first a new variety, in the latter a new subspecies is recognized.
G. divaricata from Ceylon which was mostly reduced to varietal rank is reinstated as a species. The widest spread and commonest species was mostly called G. koenigii but its proper name is G. vaginans as already recognized by Merrill in 1921.
Among the excluded taxa there are several new reductions, mostly to Psychotria: G. australiana C. T. White, G. rufinervis Stapf, and G. violascens Ridl. are all Psychotrias, but pending a revision of the latter genus I have refrained from making recombinations as they may easily appear to be superfluous. G. lasianthoides C. E. C. Fischer is reduced to Psychotria rhinocerotis Bl.; G. hongkongensis Seem, is a Randia.
Document typearticle
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