Bryum longisetum Blandow ex Schwagrichen, Sp. Musc. Frond. Suppl. 1(2): 105, plate 74 [bottom]. 1816

Plants in dense or open turfs, green or yellow-green. Stems 1-2(-3) cm, comose, innovations comose or somewhat elongate and evenly foliate; not strongly radiculose. Leaves green or yellow-green, twisted to contorted when dry, ovate to broadly ovate-lanceolate, weakly concave, 1-2(-3) mm, enlarged toward stem apex; base not or weakly decurrent; margins revolute to mid leaf or beyond, limbidium strong, in 2 or 3 rows; apex acute; costa short-excurrent, awn , denticulate; proximal laminal cells 3-4:1, same width or sometimes wider than more distal cells; medial and distal cells rhomboidal, 12-18 µm wide, 2-3:1, walls usually thin to firm. Specialized asexual reproduction absent. Sexual condition synoicous. Seta 3-6(-8) cm. Capsule brown, elongate-pyriform, symmetric, 2-4 mm, mouth yellow; operculum conic, apiculate; peristome well developed; exostome teeth yellow basally, hyaline distally, lamellae usually straight mid tooth, pores absent along mid line; endostome not adherent to exostome, basal membrane high, less than 1/2 exostome height, segments with broadly ovate perforations, cilia short, rudimentary. Spores variable in size, (38-)40-50 µm, finely papillose, pale yellow-brown or green.

Capsules mature Jun-Sep. Damp soil in wetlands; low to moderate elevations (0-600 m); Greenland; Nfld. and Labr., N.W.T., Nunavut, Yukon; Alaska; Eurasia.

Ptychostomum longisetum is a circumpolar arctic-boreal species related to P. inclinatum. Gametophytically it is similar to P. intermedium and P. salinum but differs in the extremely long seta and very large spores.