Water-splitting photosynthesis evolved about two billion years ago in organisms resembling today's cyanobacteria. One billion years ago, cells with nuclei had developed symbiotic relationships with photosynthetic symbionts becoming chloroplasts. Colonies of green protists provided the evolutionary stepping stones to the first simple plants about a half-billion years ago. Nonvascular plants Liverworts, with low-growing, flattened plant bodies, almost always are found in contact with water or wet soil. Liverworts produce male and female gametes to generate offspring that carry a combination of their parent's genetic variations.
Mosses are an adaptable and diverse group, easily collected for study.
Look for fruiting bodies and elaborate devices for spore dispersal. Sexual exchange of gametes occurs in water. Gymnosperms also are less dependent on location and weather for their reproduction, as sperm travels to egg through air-born pollen. One group, the conifers, are dominant plants today producing forest that spread through the temperate and subarctic regions of the world. Angiosperms, the flowering plants, have developed the most elaborate sexual exchanges and seed dispersal strategies.