The first plants were algae and these still thrive in a range of aquatic habitats today. Do not fall into the trap of thinking because algae have been around for so long they are “primitive”. Look upon them instead as being simple compared to more complex groups. The fact is algae today are themselves highly evolved and well adapted to the niche they occupy.
The land plants evolved from the algae, more specifically green algae, as suggested by certain shared biochemical traits;-
Energy Reserves: starch
Cell wall: based on cellulose microfibrils
Photosynthetic pigments: Chlorophylls a & b, ß-carotene
References
Chaloner, W.G. & MacDonald, P. (1980) Plants invade the land, HMSO, Edinburgh.
Thomas, B. (1981) The Evolution of plants and flowers, Peter Lowe, UK.