Description from Flora of China
Fronds very small, simple, linear, entire, glabrous. Venation consisting of a costa and at most a few almost parallel fertile veins. Sori born in a single groove along costa or on fertile veins, continuous or interrupted; paraphyses without a head, short. Spores trilete, smooth, transparent.
Vaginularia and Monogramma are both diminutive derived plants that resemble each other and cannot be distinguished properly.
About nine species: tropical Asia to Australia, and the Pacific islands; two species in China.
(Authors: Zhang Xianchun (张宪春); Michael G. Gilbert)