Funaria hygrometrica

The slits that look like mouths are stomata. They are found at the base of the Funaria sporangium, which is photosynthetic. The stomata open to let CO2 into the sporangium so that it can photosynthesize. The stomata can also close to prevent excessive water loss. These stomata are like the ones in vascular plants, except that they have a single, donut-shaped guard cell instead of the usual two bean-shaped guard cells. Many mosses have stomata with two bean-shaped guard cells.