Ribbed bog moss stalks are vertically straight and about 1.8 inches (4.5 cm) long. Ribbed bog moss is named for its distinct spore capsule, which is strongly ribbed, cylindrical, and about 4 mm long. The capsule is capped with a calyptra. Ribbed bog moss regenerates sexually and vegetatively. A spore is the first growth stage of a developing gametophyte. When the spore capsule matures, ribbed bog moss's calyptra splits along the side, exposing spores. Release of the exposed spores requires dry weather and is governed by a row of "teeth" that ring the capsule's top. The capsule teeth are hygroscopic, bending outward when air is dry and permitting spores to fall. Wind disperses ribbed bog moss spores long distances by shaking the capsule. When air is moist, the teeth bend inward, holding the spores within the capsule. The spores require a moist substrate to germinate. A germinated spore develops into a protonema (a branched, threadlike structure). Rhizoids grow down from the protonema and penetrate the substrate. Stems arise from buds that develop on the protonema surface. As stems grow, they develop their own rhizoids and become independent of the protonema. Mature male and female stems develop antheridia and archegonia, which produce sperm and eggs, respectively. Ribbed bog moss antheridia do not develop synchronously on the same stem. Mature and immature antheridia are intermixed on individual male shoots; therefore, sperm cells on the same stem do not all develop at the same time. However, sperm cells within a single antheridium have synchronous development. Fertilization requires a moist or saturated environment. Before fertilization, the antheridium absorbs water and swells, forcing the spore cap off. Rain may splash sperm into the archegonium, or sperm may swim to the archegonium. Ribbed bog moss may germinate from spores stored in the substrate, but banked spores are probably less important to ribbed bog moss regeneration than freshly dispersed spores. Ross-Davis and Frego found that annual dispersal deposited a far greater number of moss spores on boreal substrates compared to the number of spores buried in the spore bank. Ribbed bog moss is dioecious. Ribbed bog moss's sporophyte generation develops from the fertilized egg.