Cacti are grown in deserts and store water, they have thorns on them to defend against creatures trying to get the water inside. Their roots grow horizontally compared to regular roots which grow down more than it does horizontally so that it can maximise the amount of moisture it gets from the occasional rainfall which would occur around every month or so if not longer.

I learnt this in my geography class a while back because we needed to analyse features of a desert. I don’t remember much about geography and that’s all that sticks out to me.