Bryologist 31: 110. 1928. -- Dicranum flagellaceum C. Müll., Syn. Musc. Frond. 2: 597. 1851. -- Campylopus flagellaceus (C. Müll.) Mitten, J. Linn. Soc. Bot. 12: 77. 1869. -- Dicranodontium flagellaceum (C. Müll.) Williams, N. Amer. Fl 15(2): 153. 1913. -- Metzlerella flagellaceus (C. Müll.) Brotherus in Engler & Prantl, Nat. Pfl. (ed. 2) 10: 191. 1924. -- Campylopodiella flagellacea (C. Müll.) Frahm & Isoviita, Taxon 37: 968. 1988.
Plants in yellow green to green cushions or turfs, to 5 mm high. Leaves loosely erect when moist, little changed when dry, subulate above the erect and obovate base. Laminal cells in up to 8 rows on each side of the costa in leaf base. Marginal cells of leaf base somewhat more narrow than more interior basal cells. Basal cells occupying most of leaf base, rectangular and thin-walled, rectangular and thin walled, to 10 µm wide, 4–8: 1. Costa filling 1/3–1/2 of leaf base, not tapering except very near the apex, excurrent and filling all of leaf limb above the differentiated base. Hyaline awn never present. Adaxial surface of costa with thin-walled, rectangular cells, to 8: 1. Abaxial surface of costa with linear (>10: 1) cells, so thick-walled as to obscure the lumen, Costa cross-section at mid-limb with both an abaxial and an adaxial stereid band, with a single layer of medially placed guide cells and with the abaxial and adaxial epidermises poorly to well differentiated. Margin plane, entire or with a few small serrulations on shoulder. Rhizoids pale brown to brown, to 30 pm wide at base, smooth, sparingly branched from the main axis, arising on stem from immediately below leaf insertion. Axillary hairs to 300 µm long, 4-celled, with an elongate basal brown cell and with similarly elongate distal cells, of uniform diameter throughout. Stem cross-section lacking a central strand, with a leptodermous area of large and hyaline inner cortical cells and with a well-demarcated single-layered stereome of small and pigmented outer cortical cells.
Presumably dioicous but sporophytes and sexual structures not seen in our California material.