Pneumatocysts are found in clusters or single in leaf axils. S. muticum attaches to rocks with a felty, fibrous holdfast. The form also varies seasonally as upper parts are lost after reproduction. Reproductive Morphology Antheridia and oogonia develop in cavities termed conceptacles in the thallus surface. The conceptacles are grouped together on terminal fertile branchlets called receptacles.
Receptacles arise from leaf axils and are occasionally forked.
Both oogonia and antheridia are on the same receptacle but in separate conceptacles. Oogonia have 1 functional egg nucleus with 7 nuclei disintegrating.