Camellia sinensis var. assamica in Yunnan?
I find nothing to indicate it's a different cultivar, and several sources saying that it's var. assamica. My favorite couple:


An article (with photos!) on a tea merchant's site, from a guy who says he was actually in Yunnan for a year just for the tea.
A toxicology paper, with Chinese authors (though not from Yunnan).


This doesn't rule out the possibility that there are subdivisions of assamica, leading to some tiny differences between the plants. But I can find no evidence of such subdivisions. Further, given the degree to which things vary simply based on the region they were grown in (due to climate and soil) and the effects of the subsequent processing, even if there are actual differences in the plants (beyond those caused by their environment), they're unlikely to be meaningful in terms of the tea you ultimately drink.

One caveat: this is all about what's most common. But people drink all kinds of things as tea, so it's possible that you'll find tea that was made from a different cultivar with the same processing as pu-erh, and it may well be labelled as pu-erh.