Cooksonia hemispherica (family Rhyniaceae) An extremely primitive plant from the Upper Silurian and Lower Devonian belonging to a family whose members did, however, possess an epidermis and stomata to control the passage of gases. They also had an underground rooting portion, the rhizome, and they branched dichotomously. C. hemispherica is the first representative of the Rhyniaceae, and is known from the Silurian of Europe.

Cooksonia hemispherica (order Rhyniopsida) Extremely primitive plant, a few centimetres high, from the Upper Silurian and Lower Devonian. Members of the family did, however, possess an epidermis (protective outer layer) and stomata (specialized pores) to control the passage of gases. They also had an underground rooting portion, the rhizome, and they branched dichotomously. C. hemispherica is the first representative of the Rhyniaceae, and is known from the Silurian of Europe. See also PSILOPHYTALES; and RHYNIA.