Plagiomnium insigne can commonly be found growing in humid coastal forests on rotten logs and tree trunks. Additionally, Plagiomnium insigne may be located in swampy areas, alluvial sites, shaded banks, or lawns.
The leaves are strongly contorted when dry. To avoid desiccation in other species the leaves pull up against the stem, aiding in water retention. Plagiomnium insigne typically grows in shaded and moist areas, thus does not require such an adaptation. In this photo the shoot is moist.
The margin cells are elongate and form single teeth. The laminar cells are rounded.
The rhizoids are dark brown, and uniseriate with oblique crosswalls. Rhizoids do not contain chloroplasts.
The apex of the gametophyte, containing antheridia and paraphyses is surrounded by perigonial leaves. All together, these structures constitute the perigonial head. This arrangement allows for a splash cup mechanism of sperm dispersal.
The antheridia are sac-like and contain sperm. The paraphyses are contain chloroplasts, are uniseriate, and sterile.