I live on the coast of the northeastern part of Brazil (Rio Grande do Norte). As you go inland, the terrain becomes very arid. There are cactus and a lot of xerophilic plants that remind me a lot of those from southern California or Arizona. Since the sun is almost always shining here, starting a fire with a magnifying glass isn't very difficult, but if you had to do so with the bow or drill method, what Brazilian plants would work best? Fire-starting methods often involve a spindle and a hearth. What plants or woods would be most suitable for that in the interior regions of northeastern Brazil?
I am neither from Brazil nor experienced in primitive fire starting - nevertheless I will try to help.
Find out what to use as tinder
As mentioned, I don´t know a lot about Brazilian plants. Things I would try to light with matches to see how they burn before you go on a trip or get in a survival situation:
Of course there are many possible ways to prepare tinder so it burns better/longer by putting it in oil and so on, but I think thats not your intention.
Doing the bow-drill style
There are many different ways to light up that tinder, but I will only comment on this one. For the bow you need a stable stick. If the string you get (e. g. made from grass or cactus filament) is very stable you can try using a more flexible bow to get more tension in the string, but you will have to experiment with the setup a lot. For flexible bows I would suggest the only Brazilian wood I know: biribá, as is used for Berimbau instruments. But I would guess it rather grows in humid climate.
I would suggest you get also some inspiration from famous Les Stroud aka Survivorman as he also did some episodes in desert climates (look here) and covers on fire making as well as fire carrying. I think he uses the bow method in one of his episodes in Africa, but I can´t remember which.