22. Microdus Schimp. ex Besch., Mem. Soc. Sci. Nat. Cherbourg. 16: 161. 1872; Dicranella subg. Microdus (Schimp. ex Besch.) Broth., Nat. Pflanzenfam. 1(3): 309. 1901.
Plants small, slender, yellowish green, not glossy, gregarious to loosely tufted. Stems erect, simple or rarely branched, radiculose at base. Leaves carinate, lanceolate from a narrow base; margins narrowly recurved, serrulate at the apex; costa percurrent; leaf cells prosenchymatous, elongate-hexagonal to linear rectangular; basal cells shorter, becoming quadrate to hexagonal; alar cells not differentiated. Dioicous. Perichaetial leaves only slightly differentiated from vegetative leaves. Setae straight, slender, yellowish or reddish; capsules erect, ovoid to short-cylindric; opercula long-rostrate; annuli differentiated, compound; peristome teeth usually undivided, rarely divided or perforate in the tips, papillose on both surfaces above the middle, irregularly striate from base to the middle. Spores spherical, smooth or papillose.
Microdus is closely related to Dicranella, but it differs in having smaller, more delicate leaves and somewhat reduced peristome with teeth that are usually undivided, papillose, and rather irregularly striate from the base to the middle. Both genera have species with warty and papillose spores. Microdus has been treated as a synonym of Dicranella by several authors, such as Allen (1994). Species of Microdus are mainly distributed in tropical regions of the world with two distributional centers in tropical America and tropical Asia. Three species are currently recognized in China.
P.-J. Lin et al. (1992) reported Microdus miquelianus (Mont.) Besch. from Hainan Island [Jianfengling Mts., P.-C. Wu, Z.-H. Li & P.-J. Lin 85153 (IBSC, PE)], but we could not confirm the report. Microdus miquelianus is very similar to M. brasiliensis, but it differs in having more strongly thickened leaf cell walls, elongate-ovoid to narrowly cylindric capsules, and reddish setae. In contrast, Microdus brasiliensis has ovoid capsules and yellowish setae. The occurrence of this species in China needs further study.