stomium

Stomium is a botanical term referring to an opening or seam in the wall of certain sporangia, through which contents such as spores or pollen are released. The word derives from the Greek stoma, meaning mouth.

In flowering plants, the stomium most often denotes the dehiscence zone of the anther. The anther contains pollen-filled locules (thecae), and during maturation the walls rupture along the stomium to release pollen. The stomium may present as a narrow line, a groove, or a pore, and its precise form can vary among taxa. Dehiscence typically involves tearing or splitting of surrounding tissues while the stomial region remains as the opening through which pollen escapes.

The stomium is a specific feature of floral anatomy and is contrasted with other plant openings such as stomata on leaves or different dehiscence zones found in other organs. Knowledge of stomia is used in studies of flower morphology and taxonomy, and it can aid in interpreting fossil flowers where anther dehiscence patterns are preserved.

In practice, the term is most commonly applied to the anther, though it may be used, less frequently, for similar opening regions in other sporangial structures where spores or other contents are released.