I saw this cactus growing in a crack of a large granite boulder in the Wichita Moutains Wildlife Refuge, Oklahoma. I believe it is a Echinocereus pectinatus. Rex
Cactus seedlings are, ironically, more susceptible to heat and dryness than usual. A little ways down inside a rock crevice might be quite a good place for one to get started.
Now that you mention it, all the cactus I saw were tucked away in some sort of location that would protect a seedling. I find it interesting that cactus seedlings don't look like cactus. Rex
