Guinetia: A New Genus in the Tribe Ingeae (Leguminosae: Mimosoideae) from Mexico

Abstract

For many years the Isthmus of Tehuantepec in Oaxaca (Mexico) has been recognised for its distinctive flora and fauna. Shufeldt (1872) gave a comprehensive account of the biodiversity of the area. Between 1940 and 1950 Thomas MacDougall collected widely in the area and discovered many new species and genera of animals and plants (Stix 1974, 1975), so the region became a centre for collecting Cactaceae and other horticulturally important plants such as Begoniaceae and Gesneriaceae. The Leguminosae of Oaxaca project started in 1975, and since then M. Sousa and colleagues have gathered numerous plant specimens from across the whole state. As of 1996, 750 species of Leguminosae have been recorded from Oaxaca, representing 43.5% of the total number of legumes recorded for the whole of Mexico by Sousa & Delgado (1993). The new genus Guinetia, here described, was collected for the first time in 1968 on sand dunes of the Isthmus of Tehuantepec, an area from which a new species of Mimosa was also described by Grether (1981). This new genus belongs to the tribe Ingeae which is in part characterised by flowers with numerous stamens, joined into a tube for at least part of their length, and anthers without glands; Nielsen (1981) reviewed the genera in the tribe Ingeae, and stated how the classification has been based on fruit features, leading in many cases to 'pod-genera' which can be very difficult to separate when in flower. Barneby & Grimes (1996, 1997) and Barneby (1998), produced a framework of 7 alliances (groups of related genera) for the tribe Ingeae, based on growth, branching pattern and developmental characters of vegetative and floral buds. A conspectus of these is given in Barneby & Grimes (1996). Within this classification, the new genus Guinetia has characteristics both of the Chloroleucon and Inga alliances and also of the Genera incertae sedis. A comparison of features is presented in Table 1. The presence of brachyblasts and persistent perulate scales places Guinetia closer to the Chloroleucon alliance, but it matches none of the genera within that group. Within the Inga Alliance the closest genera are Calliandra, Zapoteca and Albizia (sensu Barneby & Grimes 1996: 12, 203 205 and cited under