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Gesneriaceae: |
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History
Gesneriaceae were one of the last major families to take
on its present taxonomic form. Originally two separate families were
recognized: the New World “Gesneriaceae”, In 1963, B.L. Burtt, from the Royal Botanic Garden Edinburgh, presented a new classification of Old World Gesneriaceae. He recognized that this group (subfamily Cyrtandroideae) shares a conspicuous and uncommon feature: the anisocotylous seedling. He distinguished five tribes: Cyrtandreae, Trichosporeae, Didymocarpeae, Klugieae, and Loxonieae. Additional tribes (Saintpaulieae, Rhynchotecheae, Ramondeae, Titanotricheae) were then suggested by Russian and Chinese authors, but were not generally accepted. Not included in subfamily Cyrtandroideae were the Australian and SW Pacific genera Fieldia, Lenbrassia, Negria, Coronanthera and Depanthus. These were referred to tribe Coronanthereae and, together with the temperate South American tribe Mitrarieae (Mitraria, Sarmienta, Asteranthera) added to the New World Gesnerioideae (Burtt 1963). In 1983, The German-American botanist Hans Wiehler united the tribes Coronanthereae and Mitrarieae and raised them to a subfamily of its own (Coronantheroideae). The morphological character linking its genera is that the nectary is adnate to the ovary. Thus, the last formal subdivision of Gesneriaceae (Burtt & Wiehler 1995) recognized three subfamilies:
The advent of cladistics in Gesneriaceae research (starting with Boggan 1991) and molecular systematics (starting with Smith & Carroll 1997) provided a novel set of data and showed that the former morphology-based classifications were in need of considerable modification.
Present classification of New World Gesneriaceae Regarding the New World Gesneriaceae, molecular systematics has roughly confirmed the tribes formerly distinguished, and has recognized the new tribes Sinningieae and, most recently, Sphaerorhizeae. The list of tribes thus reads:
It is important to note that the Coronanthereae indeed are closely associated with the New World Gesneriaceae. They apparently do not represent a link to Old World Gesneriaceae, though they contain several genera distributed in the Old World (New Caledonia, New Zealand, NE & SE Australia). Moreover, it became clear that Beslerieae and Napeantheae are the most primitive tribes and closely related to each other. They form a group of its own opposed to all other tribes.
Present classification of Old World Gesneriaceae Molecular systematics has proceeded less in Old World Gesneriaceae and this group is in fact more difficult to classify. It became clear that the previous subdivision into tribes cannot be maintained. Two groups can be clearly separated, the former small tribe Epithemateae (here informally referred to as Epithematoid Gesneriaceae) and the large remainder, comprising the genera of Didymocarpeae in which the members of Cyrtandreae and Trichosporeae are nested at various places (here informally referred to as Didymocarpoid Gesneriaceae). In the Didymocarpoid Gesneriaceae, a succession of the following morphological-geographical groups can be observed (Weber 2004). At the present state of knowledge an application of formal names would not make much sense:
The basal Asiatic-European genera include the Asiatic rosette plants Jerdonia and Corallodiscus as well as the three European genera Haberlea, Ramonda and Jancaea, also of rosette habit. The group comprises, however, also tall, somewhat woody plants such as Tetraphyllum, Boeica and Rhynchotechum (with indehiscent fruits). Rhynchotechum was previously asscociated with Cyrtandra and placed in tribe Cyrtandreae. Another peculiar member of that group the tiny unifoliate plant Platystemma. The African genera form a well-defined, compact group. Streptocarpus (with twisted fruits) seems to be the most primitive genus, from or in which the other genera seem to have originated. The Advanced Asiatic genera are split into two major groups: one with twisted fruits (a parallelism to the African genera?) and the large remainder with straight fruits. This is the group which comprises the species-rich and well-known genera Henckelia, Chirita, Didymocarpus, Aeschynanthus etc. The molecular data provide clear evidence that a number of genera are artificial. In particular, this confirms the view that the genus Chirita is an assemblage of largely non-related species, held together only by the technical character of a stigma with upper lobe reduced and the lower one being bilobed. The molecular data show unambiguously that this character is indicative of relationships only to a limited extent. |
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