Desert Map Tips
Go for Cotton, then the big fat round cactus, then the tea trees, then rock, then build a nice maze wall for defence…
Then scavenge, build traps and so on, also seek out a source of wood and sticks if you can, as it can be scarce in Desert Biome and you need to be planting wood early, even if only to make doors and gates.
Cotton is what’s used to make clothes. If your survivors don’t have clothes they get hypothermia and if they don’t get treated or clothes to increase their bodyheat. They die. As for food there is obviously stuff to hunt. You can also farm Heptagonia which grow on rocks and give out syrup. You can also farm some of the cactus for distasteful flowers and pickle them.
Perhaps the most significant thing you have to wrap your mind around is the absence of wood. Just about everything you make with wood on Sobrius, you have to make with stone or metal on Desertum. Observe an Oasis Tree and get those in the ground early as well, for those things for which you really want wood. After you observe it, chop it down. I was struck by your comment about finding out something you needed to know midway through the game, because I had exactly that experience when the existing Oasis Tree I was letting grow so it would get to 50/50 just dried up and withered away.
Be prepared, though: the best soil you can find for trees is only about 50 percent — and it is never handy. Oddly, it is also never the soil where you find your original oasis tree.
These two food sources should be available for you on your map atleast: