Were green algae the first plants

Yes. Green algae were considered to be the first ancestral organism to be considered part of the Plantae Kingdom. However, the first land plants appeared around 470 million years ago. These plants were a sort of moss like organism.

maritime tropical may be your answer.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).