Petrocodon retroflexus sp. nov. (Gesneriaceae) from a karst cave in Guizhou, China

Petrocodon retroflexus Q. Zhang & J. Guo, a new species of Gesneriaceae from Guizhou, China, is described and illustrated. The new species is morphologically similar to Petrocodon viridescens W. H. Chen, Mich. Möller & Y. M. Shui, but differs by its leaf blade being ovate, broadly ovate to elliptic, 8–20 × 5–15 cm and densely pilose on both surfaces, narrowly triangular, 9 mm long, densely pilose bracts, white corolla that is decurved near the middle, with adaxial lip shallowly 4-partitioned and retroflexed, and pistil ca 1.3 cm long and densely pilose and glandular-pilose.