Difference between revisions of "sporangium annulus (Q1823)"

(1.) A small ring-like protrusion from the strobilar stalk near its base and below the lowermost sporangiophores, sometimes bearing small sporangia; esp. in Equisetum. (2.) A row of protruding specialized sporangial wall cells that extends upward from the base of the sporangium and over its apex, thus forming an incomplete circumferential ring; esp. in Polypodiophyta. The inner and radial walls of the annular cells are markedly thickened and the structure functions as a spore-releasing and -disseminating mechanism as a result of differential stresses developed within the mature sporangial wall upon desiccation.