Fissidens tumescens is described and illustrated from Dominica and Guadeloupe in the eastern Caribbean Sea. The species belongs to subgenus Aloma, and is most similar to F. neglectus. Its distinctive features include: slender leafy stems; intralaminal, unistratose limbidia that extend to about ½–¾ the length of the vaginant laminae of most leaves; smooth, tumid laminal cells that vary from unistratose to bistratose; and, marginal laminal cells often papillose on the margins.