They are not plants, see below for explanation
mars.jpl.nasa.gov...
From The MGS website,
Because the martian air pressure is very low--100 times lower than at Sea Level on Earth--ice on Mars does not melt and become liquid when it warms
up. Instead, ice sublimes--that is, it changes directly from solid to gas, just as "dry ice" does on Earth. As polar dunes emerge from the
months-long winter night, and first become exposed to sunlight, the bright winter frost and snow begins to sublime. This process is not uniform
everywhere on a dune, but begins in small spots and then over several months it spreads until the entire dune is spotted like a leopard