I look at the solar system as Australia; Mars got the red deserts, Venus got all the poisonous shit, Mercury got the heat, and Luna the politicians.
A bit more seriously; I use the pop-culture representation of the australian outback as a mental image for Capitol's homeworld, right or not. Complete with cattle drives, rugged prospectors and Mad Max'es.
And I'm sure it has both vegetation and interesting wildlife. Isn't much of the southern hemisphere shallow ocean? Or was that something else?
Last I checked, the southern hemisphere of Mars is like large swathes of the southern United States - lots of wide open deserts, plains, and grasslands - it's the Old West, writ large across half a world. Capitol doesn't own the whole lot - there are portions that are desolate wastelands controlled by the Dark Legion (the 'Doughpits'), portions controlled by Imperial, and portions controlled by Mishima.
Northern Mars is, if memory serves, the more heavily-settled part of the planet, with the majority of the big cities (like San Dorado) there.
Mars certainly has plant and animal life - 80% of Capitol's food production comes from a region of plains and farmland known as the Freedom Lands in the southern hemisphere.
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