J Syst Evol ›› 1996, Vol. 34 ›› Issue (4): 341-360.

• Research Articles •     Next Articles

The Geographical Distribution of the Subfamily Cyrtandroideae Endl. Emend. Burtt (Gesneriaceae)

Li Zhen‐yu   

  • Published:1996-07-10

Abstract: Based on Burtts classification and relevant references, the geographical distribution of the subfamily Cyrtandroideae Endl. emend. Burtt is outlined, distribution maps of 79 genera are provided, and some evolutionary trends of the taxa are inferred. The main points may be summarized as follows:1. The centre of distribution The Cyrtandroideae consists of four tribes, 79 genera and about 1770 species, widely distributed in tropical and subtropical regions of the Old World, ranging from Guinea eastwards to Nukuhiva Islands and from Western Bulgaria southwards to Southern Natal, with only one species disjunctly occurring in tropical America. According to Takhtajans (1978) regionalization of the world flora, and referring to Goods (1974) and Wus (1979) scheme, the distribution patterns of Cyrtandroideae may be generalized as: (1) Pantropics, with 3 genera; (2) Palaeotropics, with 47 genera; and (3) North Temperate, with 27 genera. Tropical Asia (Indo Malaysia) is the centre of variation and diversity of the Cyrtandroideae, where the most primitive taxa, with the chromosome number of n=8 or n=9, and all of the four tribes exist, and where more genera(50) and species (1200 odd) are found than elsewhere. Among the four tribes of the Cyrtandroideae, only two tribes are distributed west of India. Three European genera with six species, confined to the Mediterranean, belong to one tribe, Didymocarpeae. Of 10 African and Madagascar genera, 9(7 endemic) belong to Trib. Didymocarpeae, 1 to Trib. Klugieae, and a11 of 168 African and Mada gascar species are not outside both of these regions. 2. Disjunct distribution and dispersal In Trib. Klugieae, two species of Epithema are found disjunctly in west Africa, and one species of Rhynchoglossum, R. azureum, is disjunct in tropical America, from southern Mexico to northern Peru. Their closely allied species and neighbouring genera are in tropical Asia. Rhynchoglossun azureum has a close relationship with R. notonianum, which is located in India and Sri Lanka, so it is hypothesized that Rhyncho glossum existed in north Africa, where there were tropical rain forests similar to those in Malaysia during the Tertiary. The author noticed that seeds of R. obliquum from tropical areas of southern Yunnan can still germinate after seven months at normal temperature. Most seeds of this genus are not only long lived but very tiny (0.3~0.4 mm long), and can be dispersed by wind or birds (epizoochore through the agency of mucus). One or two species of Rhipsalis in Cactaceae was carried by birds from south America to Madagascar, the Mascarene Islands and Sri Lanka at an early period. This example indicates the possibility of this means of distribution. More than 200 species from the volcanic islands of the Polynesian region, including the Hawaiian Islands,all belonging to Cyrtandra, were obviously spread by birds from tropical Asia during an earllier period. The distribution of two species of Boea and one species of Cyrtandra in northeast Queensland shows that some early taxa of the genera entered Yorke Peninsua from New Guinea when the sea level was lower during the Quaternary glaciations The modern vicarious distribution patterns of the two subfamilies indicate that the main taxa of the family were produced during the course of the continental drift and the climatic and environmental changes. According to the principle of common origin, the ancestor of Gesneriaceae appeared most probably not later than the late Cretaceous, and might be traced back to the Mid Cretaceous. 3. Some problems about evolutionary tendencies In general, the actinomorphic corolla precedes the bilabiate one, and the flower with stamens all fertile precedes those with 1 or 3 staminodes (Ivanina, 1965; Wang, 1989、 1992). In some diandrous genera of Cyrtandroideae, 4 or 5 fertile stamens may occur exceptionally, and are associated with a more or less regular corolla. The exceptional appearances may possibly be atavistic, not representing the main evolutionary tendencies. In the genus Aeschynanthus, pollen grains of Sect. Haplotrichum and Sect. Diplotrichum, whose corollas usually have indistinct bilabiate limbs, are comparatively small, but large in sections Microtrichium, Xanthanthos and Aeschynanthus, whose corollas have distinct bilabiate limbs. 4. The relationships of the four tribes he tribes Cyrtandreae, Trichosporeae and Didymocarpeae are closely related (Kvist and Pedersen, 1986). Some terrestrial plants of Trib. Trichosporeae (e.g.Anna and Lysionotus Sect. Didymocarpoides), in which the seeds have subulate appendages at their ends, may represent the intermediate links between tribes Didymocarpeae and Trichosporea.Boeica and Hexatheca form natural links between the tribes Cyrtandreae and Didymocarpeae. The tribes Didymocarpeae and Klugieae probably originated from a common ancestor at an early stage in the evolution of the family.

Key words: Cyrtandroideae, distribution patterns, evolutionary tendencies, systematic relationships