Sphagnum trinitense C. Müll., Syn. Musc. Frond. 1: 102. 1848.

Sphagnum laxifolium var. serrulatum Schlieph., Verh. Zool.-Bot. Ges. Wien 15: 397. 1865. Sphagnum cuspidatum var. serrulatum (Schlieph.) Schlieph., Irmischia 2: 67. 1882.

Plants relatively robust (to 12, rarely 45 cm long), pale yellow-green to yellowish, in lax, floating mats; cortical cells long, narrow, poorly differentiated in 1–3 layers; wood cylinder yellowish. Stem leaves concave, oblong to ovate, acute to blunt or rounded-obtuse, often erose at the apex, not or somewhat broad-bordered at base; hyaline cells fibrillose throughout or sometimes only above, few to many (usually) 1-divided, on the outer surface without pores or gaps, on the inner surface with fibrils and 2–5 small, round pores or with fibrils vestigial to lacking and 2–4 median gaps, or the membrane largely resorbed, both surfaces largely resorbed near the leaf apex. Branches in fascicles of 4 (rarely 5) (with 2 deflexed), sometimes cuspidate-tipped but more often ending in a loose tuft of long-tapered leaves that are flexuous-contorted when dry; retort cells differentiated. Branch leaves when young (in the capitulum) often rather short and broadly truncate or rounded at the apex, the others narrowly lanceolate and long-tapered (longer and narrower toward the branch tips), involute-concave when moist, flatter and wavy-margined when dry, with bordered margins serrulate in the upper third, half, or nearly throughout (more distinctly so at tips of long upper leaves), hyaline cells slightly convex on the inner surface; on the outer surface with pores 1–2 (rarely 3) very small, inconspicuous, and round, at ends and corners, sometimes lacking, on the inner surface with 3–6 (rarely 8) small, indistinct, unringed, round pores at ends and corners, sometimes also at commissures.