The Gentianaceae of the Neotropics are a diverse taxonomic group representing several evolutionary lineages. The phylogenetic relationships of neotropical gentians are discussed based on cladistic analyses of morphological, trnL intron, and ITS 1 sequence data. Support for specific morphological and anatomical character evolutionary and biogeographic hypotheses are evaluated, with an emphasis on taxa from the Guayana Shield.
Saccifolium, the only member of the family Saccifoliaceae, was found to be closely related to Gentiana and associated temperate-alpine genera. The boreotropics hypothesis is suggested as an explanation for the isolated occurrence of Saccifolium on the tepui complex Sierra de la Neblina (Brazilian-Venezuelan border), far from possible close relatives in eastern North America. Saccifolium is now considered a member of Gentianaceae due to this result.
The majority of neotropical gentians belong to the Helia clade, a monophyletic, natural group restricted to the Neotropics. The Helia clade shows great morphological variation and occur in a diversity of habitats and geographic areas. Secondary woodiness appears to have evolved independently in this clade and in the Potalia clade, with perennial herbs being ancestral. Floral characters are also discussed from a phylogenetic perspective. The Helia clade has a high rate of white-sand and tepui endemic species including some that have been recently described. Several white-sand species are suggested to be relicts of basal evolutionary lineages in the tribe. The Pantepui and Quaternary forest refugium theory is discussed, and preliminary data suggest several independent origins of highland taxa from lowland lineages.
The genus Potalia is most closely related to the African and Malagasy genus Anthocleista and it is suggested that the boreotropics hypothesis also explains their distribution. The first monograph of Potalia is presented. Potalia amara, the type species, is restricted to French Guiana and Amapá, Brazil. Three additional species are restricted to white-sand areas in lowlands of Amazonia and the Guayana Shield, and two species are restricted to Chocó, Colombia, and Panama and Costa Rica, respectively. Potalia resinifera is the most widespread species occurring over most of the Amazon basin, Andean foothills, and the Chocó. A morphological cladistic analysis of Potalia is presented, and this supports the proposed theory of white-sand taxa being representatives of basal, relictual lineages in neotropical plant groups (as in the Helia clade).<>P A cladistic analysis of the mycotrophic genus Voyria based on morphology and anatomy resulted in two large, monophyletic lineages, identified as two new subgenera. Ancestral distributions of Voyria and Potalia on the Guayana Shield are supported by morphological cladistic studies.
Stockholm: Stockholm University , 1999. , 32 p.