Codonanthe (Martius) Hanstein and Nematanthus Schrader (Gesneriaceae) are morphologically distinct genera of the evergreen and deciduous rain forests of Central and South America. Two subgenera andtwo sections had been recognized to accommodate the fourteen cultivated species of Codonanthe, whereas no subgeneric ranks were previously reported for the ten cultivated species of Nematanthus . Hybridizations between Codonanthe and Nematanthus have produced progeny that display a high degree of fertility, indicating that the species of Codonanthe and Nematanthus are closely related. The present study examined the species of Codonanthe and Nematanthus and attempted to resolve the relationship of species between genera and within each genus. Conventional taxonomic methods and systematic techniques of light and electron microscopy, microtomy, leaf clearings and karyology were utilized in the study of live plant material.
Flowers of Codonanthe species have obliquely funnel form-ventricose corollas that are primarily white and are presumably pollinated by Euglossine bees, whereas species of Nematanthus have pouched corollas that are basically orange, red, pink or yellow and are presumably pollinated by hummingbirds. Possession of such differing corolla types and pollinators reproductively isolate these two genera, possibly indicating that Codonanthe and Nematanthus should remain as distinct taxa.
Species of subgenus Codonanthe section Codonanthe have orange berries, a diploid chromosome number of n=8, and a unilacunar nodal anatomy (except C. carnosa and C. gracilis), lack extrafloral nectaries, and are indigenous to southeastern Brazil. Species of subgenus Codonanthe section Spathuliformae and subgenus Codonanthella have red, pink or purple berries or yellow-green fleshy capsules, a tetraploid chromosome number of n=l6, and a trilacunar, split-lateral nodal anatomy, possess extrafloral nestaries, and are geographically widespread from southern Mexico through Central America to northern South America. Nematanthus crassifolius , N. fissus, N. fritschii , N. hirtellus , N. maculatus and N. perianthomegus have a shrubby growth habit, trilacunar, spilt-lateral nodal anatomy, and resupinate flowers, whereas N. gregarius , N. nervosus , N. strigillosus and N. wettsteinii have a viny growth habit, unilacunar nodal anatomy, and nonresupinate flowers.
On the basis of these observations, sections Nematanthus and Farvifolius are established to accommodate the species of Nematanthus, and it is acknowledged that further studies are required before any conclusions are made on the relationships of the infrageneric taxa of Codonanthe . A synopsis of the infrageneric taxa and revised classification of the genera Codonanthe and Nematanthus is presented.