Plants moderate-sized to robust, weak-stemmed; pale brown to chestnut brown; capitulum flat-topped and generally 5-radiate, branches straight to somewhat curved, terminal bud often visible. Stems pale green to brown, superficial cortex of 2 layers of thin-walled and well differentiated cells. Stem leaves triangular, ovate-triangular to triangular-lingulate, 1-1.3 mm; appressed to spreading; apex obtuse, hyaline cells usually fibrillose near apex. Branches straight to somewhat curved, leaves moderately elongate at distal end. Branch fascicles with 2 spreading and 1-2 pendent branches. Branch stems green, cortex enlarged with conspicuous retort cells. Branch leaves ovate-lanceolate; usually more than 2 mm; straight; weakly undulate and slightly recurved when dry, margins entire; hyaline cells on convex surface with numerous small free pores in proximal 2/3 of leaf and in apical region with numerous pseudopores along commissures, on concave surface with numerous round free pores; cells relatively long and narrow in basal region, much longer than in mid region; chlorophyllous cells triangular in transverse section and well-enclosed on concave surface. Sexual condition dioicous. Spores 29-33 µm; both surfaces very smooth; proximal laesura long, more than 0.6 spore radius.
Predominantly in wet carpets in poor to medium fen habitats, mostly in mire-wide vegetation; low to moderate elevations; Alta., B.C., Nfld. and Labr. (Nfld.), N.W.T., Ont., Que., Sask., Yukon; Alaska; Eurasia.
Sporophytes of Sphagnum jensenii are uncommon. For more information, see discussion under 23. S. annulatum.