Martians are inhabitants of the planet Mars. Martians are stronger and more durable than humans, capable of shapeshifting, super strength, intangibility and flight, can adapt to various environments including that of Earth, and are telepathic. Martians have two genders, and marriage and familial relationships are apparently similar to those of humans. The entire Martian population was wiped out by the Imperium except for J'onn J'onzz.
It seems Martian males and human males do have similarities in their genes as Aresia's antigen, which was made to only target males, affected J'onn as well.
In the DC comics, there are two distinct Martian races, the Green Martians, which are what the DCAU Martians are based on, and the White Martians. The two were once a single race, but their belligerence led the Guardians of the Universe to separate them into two species: the Greens became a race of peaceful philosophers, while the Whites became a race of savage warriors. One of the Whites, M'gann M'orzz, rejected her species violent culture and joined the Teen Titans.