Phylogeny and biogeography of Gunnera

• The angiosperm genus Gunnera consists of 30-40 species mainly distributed in Africa, New Zealand, Tasmania, South America, the Malay Archipelago and Hawaii. Because of its distribution in almost all parts of the Southern Hemisphere and to its 90 millions year's history on Earth, Gunnera is especially interesting for its biogeography. By analysing sequences of rbcL and the rps16 intron from the chloroplast, and the ribosomal DNA ITS region from the nuclear genome, and by studying the morphology of 27 species representing all six subgenera of Gunnera (Panke, Misandra, Milligania, Gunnera, Pseudogunnera and Ostenigunnera), a wellsupported phylogeny for the genus was obtained for the first time. The biogeography of Gunnera was then examined in the light of the phylogeny. The positions of G. herteri and G. perpensa, from northern South America and Africa, respectively, were well supported in the phylogeny and interpreted as what remains of the species that once inhabited the large area along the Guinea fracture zone to which both Africa and northern South America belong. The remaining species were divided into two clades; one including the Malayan/Australian/New Zealand species and the other with the American and Hawaiian species. Within the first clade, the position of the Malayan G. macrophylla sister to the species from New Zealand and Tasmania was interpreted as a vicariance event. In contrast, G. cordifolia from Tasmania, nested within the species of New Zealand can be explained by dispersal from New Zealand. In subgenus Panke, the positions of G. mexicana and of the Hawaiian species, respectively, as sisters to the southern South American species suggests a northern origin for the subgenus. Though the resolution within subgenera Milligania and Panke is not yet complete, a good framework for future studies has been established.The phylogeny allows also for the first time other taxonomic and morphological types of studies. The South American G. manicata is the most commonly cultivated species. The identity and the origin of this species have long been controversial. The molecular phylogeny of Gunnera clarified that the place of origin of G. manicata is Brazil. The specimens from Colombia, which mistakenly goes under the name G. manicata, represent a new species.On the apex of the rhizomes of all the South American and Hawaiian species (subgenus Panke), there are large scales which have been the focus of discussions during the past two centuries. The scales have sometimes been interpreted as cataphylls and sometimes as stipules. Botanists have also searched for structures homologous to these scales in other species of the genus. According to the present results, the scales in Panke are of leafy origin and homologous to two cataphylls on the top of the stolons of the plants of subgenera Pseudogunnera and Milligania. The scales are also homologous to the ochrea found on the stolons in subgenus Misandra.

Ämnesord

NATURVETENSKAP  -- Biologi -- Botanik (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Botany (hsv//eng)

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Växter

fylogeni

Tvåhjärtbladiga

Magnoliopsida

systematisk botanik

Systematic Botany

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