Sphagnaceae Dum., Anal. Fam. Pl. 68. 1829.
Li Xing-jiang and Si He
Plants small to robust, whitish green to yellowish brown, sometimes tinged with purple or reddish color, in mats, cushions or hummocks, growing in wet habitats or in peat bogs above water level, infrequently submerged in water. Protonemata thallose, producing 1, rarely 2, leafy gametophores, sometimes filaments formed on the thallus margins initiating secondary protonemata from the terminal cells of the filaments. Rhizoids very few, restricted to the base of young gametophores, absent on the mature gametophores. Stems erect, simple or sparsely branched; stem tissues consisting of three distinct layers with thin-walled parenchyma centrally surrounded by a colored wood cylinder of thick-walled prosenchyma and enclosed by 1 or more layers of large, thin-walled, empty (hyaline) cortical cells, sometimes with spiral fibrils. Branches often arranged in fascicles, spirally disposed around the stems, each fascicle often consisting of two or more divergent branches and two or more slender pendent branches, in some species stems simple, with 1–3 branches per fascicle; branches usually crowded at the stem tips forming a head-like tuft or capitulum; branch cortical cells often with numerous enlarged, apical pores, at times with fibrils. Stem leaves spirally and widely spaced, usually differentiated in size, shape, and structure from branch leaves; mature stem leaves with little or no chlorophyll, the divided hyaline cells often with a weak development of pores and lack of transverse fibrils, showing extensive resorption of the walls with membrane pleats or irregular membrane gaps. Branch leaves spirally arranged in more or less 4–5 rows, often bordered by several rows of linear cells, enclosing a network of elongated green cells surrounding large, empty hyaline cells; the hyaline cells nearly always reinforced by ringlike fibrils and porous at the surfaces. Dioicous or monoicous; branches always unisexual with antheridia and archegonia on separate branches; paraphyses none; antheridia globose with a long stalk, with one antheridium at the base of each perigonial leaf, growing on specialized divergent branch tips that are often deeply pigmented with red or brown color; archegonial branches single, rarely double, bearing 1–5 archegonia at the apex of each branch. Perichaetial leaves often considerably larger than vegetative leaves, usually enclosing the sporophytes until maturity. Sporophytes consisting of a capsule and a foot, nearly sessile, elevated at maturity by elongation of the gametophytic stalklike pseudopodium at the tips of archegonial branches; true setae not developed; capsules globose, dark-brown to black; opercula developed; annuli none; peristome absent; stomata rudimentary, consisting of a pair of guard cells without a pore; columella dome-shaped overarched by large, tetrahedral spores. Calyptrae delicate, with hyaline membrane covering the opercula and irregularly ruptured when capsules mature. Spores large, tetrahedral, overarching columella.
The family consists of a single genus, Sphagnum L.