The genus Radermachera Zollinger and Morit comprises about 16 species, mainly distributed in tropical Asia, there are 7 Radermachera species in Vietnam. Based on the analysis of specimens and documents of Gesneriaceae of Vietnam, we found Radermachera microcalyx C. Y. Wu & W. Yin in Lao Cai province, North Vietnam. Radermachera microcalyx is tree, ca. 20 m tall. Leaves compound pinnately I times, ca. 40-60 cm long
leaflet 5-7 pairs, ovate or elliptic, ca. 11-26 x 4-6 cm, margin entire, lateral 6-10 pairs. Inflorescences thyrsus, terminal
calyx campanulate, 5 small teeth, apex truncate
corolla pale yellow, tube ca. 2-2,5 mm long
style filiform
capsule line, dehiscung by 2 valves
seeds many, minute. This species is closed to R. glandulosa but differs by having leaves dim glandular in abaxial, corolla tube 2.0-2.5 cm long, ca. 4-5 mm in diam. Voucher specimens were collected in Hoang Lien - Van Ban reserve, Lao Cai province and deposited in the Herbarium of the Institute of Ecology and Biological Resources, Hanoi, Vietnam (HN).