A Review of the Genera Roentgenia and Potamoganos (Bignoniaceae)

Abstract

Roentgenia and Potamoganos (Bignoniaceae) are small genera of lianas with corollas that are closely related to larger and more well known genera such as Cydista, Clytostoma, and perhaps Phryganocydia. Roentgenia is ditypic, containing R. bracteomana and R. sordida, whereas Potamoganos is monotypic, containing only P. microcalyx. The two species of Roentgenia have white to lavender, campanulate-funnelform, Cydista-type corollas, stems with eight phloem arms, bi-trifid tendrils, 3(-4)-colpate pollen with reticulate exine, 2-seriate ovule organization, nectariferous disk lacking, linear-oblong fruit, and winged seeds. Roentgenia bracteomana is distributed from southern Colombia to northern Bolivia and north-central Brazil, whereas R. sordida is restricted to eastern Venezuela, Guyana, Suriname, French Guyana, and portions of northern Brazil. Potamoganos microcalyx has lavender to magenta, campanulate-funnelform, Cydista-type corollas, with four phloem arms, trifid tendrils, 3-colpate pollen with reticulate exine, 4-seriate ovule organization, and a nectariferous disk. Potamoganos microcalyx is known from southern Venezuela, Guyana, Suriname, and northernmost Brazil. A key to species, maps of species distributions, reproductive phenology, and illustrations of R. bracteomana and P. microcalyx are provided.