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Gesneriaceae: |
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The geographical distribution of the Gesneriaceae can be roughly characterized as pantropical and pansubtropical, that is occurring in the tropical and subropical zones around the globe. However, there are remarkable extensions into the south and north, e.g. into temperate South America, Europe and northern China. When going into more detail, it is best to refer to the major subgroups of Gesneriaceae: Coronantheroid Gesneriaceae: Restricted to the southern hemisphere; NE Australia (Lenbrassia), SE Australia (Fieldia), SW Pacific islands (Negria on Lord Howe Island), Solomon Islands (one sp. of Coronanthera), New Caledonia (Coronanthera, Depanthus), New Zealand (Rhabdothamnus), and temperate South America (Chile and adjacent Argentina: Mitraria, Sarmienta, Asteranthera). Gesnerioid Gesneriaceae: Essentially southern North America (central and southern Mexico), Central America and tropical South America, southwards to SE Brazil and Northern Argentina and Uruguay (esp. Sinningia and allies). Epithematoid Gesneriaceae: South and Southeast Asia to New Guinea, one species of Epithema (E. tenue) in West Africa and one species of Rhynchoglossum (R. azureum) in Central America to Venezuela (but both belonging to genera centered in Asia). Didymocarpoid Gesneriaceae: South, East and Southeast Asia, the Philippines, the Malay archipelago from Sumatra to New Guinea (largely but not entirely corresponding to Indonesia) (the bulk of genera), Polynesia (Cyrtandra); East, West and South Africa, Madagascar (Streptocarpus and allies); southern Europe (Ramonda, Haberlea, Jancaea). Gesneriads are often regarded as tropical counterparts of the essentially temperate family Scrophulariaceae. This view, however, needs specification and partly correction. (1) In contrast to traditional belief, Gesneriaceae are not an offspring of Scrophulariaceae (which themselves are nowadays split into several families such as Scrophulariaceae, Plantaginaceae, Calceolariaceae, Paulowniaceae, Schlegeliaceae, Stilbaceae etc.), but seem to have an independent origin. (2) Though many genera and species occur in the tropics, in phylogeny the tropical areas seem to have been secondarily invaded from warm-temperate and subtropical regions. The distribution of gesneriads should no longer be compared and paralleled with tropical plants such as palms (as is often done in textbooks), as their origin is most probably extra-tropical. |
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