The biogeography of Gunnera L.: vicariance and dispersal

Abstract

Aim The genus Gunnera is distributed in South America, Africa and the Australasian region, a few species reaching Hawaii and southern Mexico in the North. A cladogram was used to (1) discuss the biogeography of Gunnera and (2) subsequently compare this biogeographical pattern with the geological history of continents and the patterns reported for other Southern Hemisphere organisms. Location Africa, northern South America, southern South America, Tasmania, New Zealand, New Guinea/Malaya, Hawaii, North America, Antarctica. Methods A phylogenetic analysis of twenty‐six species of Gunnera combining morphological characters and new as well as published sequences of the ITS region, rbcL and the rps16 intron, was used to interpret the biogeographical patterns in Gunnera. Vicariance was applied in the first place and dispersal was only assumed as a second best explanation. Results The Uruguayan/Brazilian Gunnera herteri Osten (subgenus Ostenigunnera Mattfeld) is sister to the rest of the genus, followed sequentially upwards by the African G. perpensa L. (subgenus Gunnera), in turn sister to all other, American and Australasian, species. These are divided into two clades, one containing American/Hawaiian species, the other containing all Australasian species. Within the Australasian clade, G. macrophylla Blume (subgenus Pseudogunnera Schindler), occurring in New Guinea and Malaya, is sister to a clade including the species from New Zealand and Tasmania (subgenus Milligania Schindler). The southern South American subgenus Misandra Schindler is sister to a clade containing the remaining American, as well as the Hawaiian species (subgenus Panke Schindler). Within subgenus Panke, G. mexicana Brandegee, the only North American species in the genus, is sister to a clade wherein the Hawaiian species are basal to all south and central American taxa. Main conclusions According to the cladogram, South America appears in two places, suggesting an historical explanation for northern South America to be separate from southern South America. Following a well‐known biogeographical pattern of vicariance, Africa is the sister area to the combined southern South America/Australasian clade. Within the Australasian clade, New Zealand is more closely related to New Guinea/Malaya than to southern South America, a pattern found in other plant cladograms, contradictory to some of the patterns supported by animal clades and by the geological hypothesis, respectively. The position of the Tasmanian G. cordifolia, nested within the New Zealand clade indicates dispersal of this species to Tasmania. The position of G. mexicana, the only North American species, as sister to the remaining species of subgenus Panke together with the subsequent sister relation between Hawaii and southern South America, may reflect a North American origin of Panke and a recolonization of South America from the north. This is in agreement with the early North American fossil record of Gunnera and the apparent young age of the South American clade.

Phylogenetic systematics of Hoya (Apocynaceae)

“…2). A sister relationship between taxa from New Guinea and taxa from Australia is concordant with the results of other phylogenetic studies and is consistent with the fact that New Guinea and Australia lie on the same continental plate (McLoughlin 2001), and taxa from these two areas are often found to be closely related (e.g., Linder & Crisp 1995, Wanntorp & Wanntorp 2003. The species of Hoya examined have large flowers with bell-shaped corollas (Fig.…”

New insights into the pollen morphology of the genus Gunnera (Gunneraceae)

“…Subgenera Misandra, Milligania and Panke comprise several more species than those included in the present study. The species of each subgenus are, however, very similar in morphology (Wanntorp & Wanntorp 2003) and we believe that a different taxon sampling would therefore not affect the results of this study. Due to the stenopalynous nature of the genus (Praglowski 1970), the pollen morphology of Gunnera can not be used for species identification and the inclusion of only ten species from the over 40 described within the genus, but representing all subgenera, was considered adequate.…”

“…2. Changes of pollen morphological characters plotted on a cladogram representing the phylogeny of Gunnera (redrawn from Wanntorp & Wanntorp 2003). Subgenera are shown in capitals below the names of each species.…”

“…The redrawn phylogeny used in the present paper is based on the study of Wanntorp & Wanntorp (2003).…”

“…However, the uniformity of the pollen grains in Gunnera allowed a confident association with pollen of the fossil species T. reticulatus to Gunnera. Today, we know that Gunnera was widespread in Africa, Australia, and New Zealand 80 million years ago, which suggests a Gondwanan origin for this genus (Wanntorp & Wanntorp 2003). Jarzen & Dettman (1989) studied specimens of T. reticulatus from southern Australia, Antarctica, and the Kerguelen Plateau by scanning electron microscopy.…”