Plants slender, pale green to yellowish green, 2--8 cm, reclining. Stems small, pale yellowish brown, creeping, closely affixed to substratum, epidermal cells not hyalodermous, central strand weakly developed; usually irregularly to regularly pinnately branched, branching arising in horizontal plane, pseudoparaphyllia subfilamentous to lanceolate, tipped by elongate cell. Leaves weakly to strongly falcate-secund, ovate- or oblong-lanceolate, tapering gradually to base and tapering gradually to a short or more usually long acumen, 1--1.8 × 0.35--0.60 mm, margins usually sharply serrulate, often recurved near base, costa double, short or indistinct; median cells (40)50--60(--70) × 4--5 µm, basal cells shorter and wider, usually yellow or yellowish brown, alar region weakly excavate, often brown, of subquadrate cells (5--)7--10(--13) along margin, the marginal ones enlarged and hyaline, the inner brownish. Sexual condition dioicous; inner perichaetial leaves erect, oblong-lanceolate, suddenly narrowed to a long, serrulate acumen, costa obscure. Seta yellowish to reddish brown 0.08--1.7(--2) cm. Capsule yellowish to reddish brown, erect to inclined, oblong-cylindric 1.5--1.8(--2) mm; operculum conic (rounded-mammillate); annulus 2--3 seriate; cilia of endostome single or imperfectly double, very fragile.

Sporophytes produced in late autumn (September), capsules often maturing in spring (Mar.--Apr.), infrequent. Perpendicular surfaces of tree trunks and rock cliffs; 0--2000 m; Nfld, N.S.; Maine; Europe.

Hypnum andoi is a temperate species of amphi-Atlantic distribution. This species resembles Hypnum cupressiforme var filiforme, but the row of basal hyaline cells in the alar region of the former is decidedly different, reminiscent of Sematophyllum; the shorter, stouter capsule, and mammillate operculum are also valuable characters. Sporophytes are extremely rare in North America, and have a conic operculum rather than a mammillate one, as in Europe.