Please, help. Moss?

Question

Why can moss grow in the unsuitable conditions for life of other plants?

Answer 1

Mosses & liverworts were early terrestrial colonizers in prehistory and retain that ability today. They can withstand long dormant periods of either drought or cold to await the return of good growing conditions. They are tolerant of high UV exposure. This is why they are the plants found in Antarctica though only in the few areas that have free water such as lake shorelines or stream sides. Basically anyplace with accumulated melt water.
Moss creates a dense low cover that acts to sustain its preferred habitat in a succession within its community composition. Colonist/pioneer mosses are followed by habitat mosses and liverworts but also support refugium classes to reestablish should there be habitat disruption.

http://www.nationalgeographic.com/geographyaction/habitats/deserts_tundra.html
http://www.pnas.org/cgi/content/full/103/3/637
"cushion moss Grimmia laevigata Bridel grows on bare rock in a broad range of environments on every continent except Antarctica" but looks to be the same plant despite the environmental extremes it inhabits. Bridel's genome reveals its survival is linked to alleles distinct to each geographic location that confer variation to its habitat survival without obvious morphological changes.

Answer 2

Evolution, it evolved to it's conditions and has become a very hardy and successful plant.