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.