Porotrichum microthecium is a leaf species described by C. Müller in 1897. Porotrichum microthecium is part of the genus Porotrichum and the Neckeraceae family . Plants medium-sized, dendroid, light green to golden green, shiny. Stems forming stipe perpendicular to substrate, usually pinnate to sparsely branched distally; paraphyllia absent. Secondary stem and branch leaves erect, ovate-oblong, asymmetric, flat; margins serrate, teeth straight; apex acute; costa single, , tapering toward apex; basal and medial laminal cells rectangular, walls not porose. Sexual condition dioicous; perichaetial inner leaves broadly lanceolate-subulate. Seta to 2.5 cm. Capsule oblong-ovoid; exostome teeth lanceolate, external surface with strongly projecting lamellae, usually papillose; endostome basal membrane high, segments papillose to sparsely papillose. Spores 13 -m.Species ca. 40 (1 in the flora): w North America, Mexico, West Indies, Central America, South America, Asia, Africa, Pacific Islands (New Zealand).