Rhynia

Emergence from the waters

Rhynia

Towards the colonisation of the continents

The emergence from the waters was a major event in the history of the vegetation of our planet; prior to this, the continents were just mineral deserts. The colonisation of the shores took place during the Upper Silurian (420 Ma) due to a number of fundamental innovations:

• the development of the cuticle and stomata (specialised openings that contribute to gaseous exchange) which prevent desiccation;
• the vascularisation of axes allowing the circulation of water and nutritive elements in all parts of the plant;
• the development of turgor pressure which lends rigidity;
• finally, the production and dispersal of spores allowing them to spread.

Hepatics, pioneering plants of dry land, have a mode of reproduction that includes an embryo stage reminiscent of that of mosses and other more complex terrestrial plants.

Cooksonia is one of the earliest vascular plants found in the ancient sediments of many regions. It formed a mat, some 30 centimeters in height, immerged to varying degrees on the continental margins.