acalymmate adjective1 •Forming clusters of pollen grains (usually tetrads or polyads) in which the sexines of the respective grains do not merge to form a continuous sheath.When loosely associated, each tetrad retains most of its outer exine layer, leading to calymmate tetrads, but an acalymmate massula (since the exine is not continuous around each massula […]). — 1996
