Three hollies, one genus
Yerba mate, guayusa and yaupon are all Ilex and all contain caffeine. Mate is farmed at industrial scale across the Paraná basin; guayusa grows in Amazonian house gardens in Ecuador; yaupon is native to the southeastern United States and was traded inland as far as Cahokia. They differ mainly in bitterness, in that order.
The gourd is not decoration
Mate is drunk from a shared gourd through a metal straw, refilled and passed by one server in a fixed order. The etiquette is specific enough that getting it wrong is noticed — you do not stir with the bombilla, and returning the gourd with thanks signals that you have finished. This is a social form, not a serving suggestion.
Tereré, and the cold version
In Paraguay and parts of Argentina and Brazil the same leaf is drunk cold, with iced water and often citrus, under a different name. It is the summer form of the same practice rather than a different product, and it is more common than the hot version in the places that drink it.
Cuts, and what the labels mean
Con palo includes stem and sin palo does not, and the difference in the cup is real — stem softens the bitterness and dilutes the leaf. Brands vary enormously in how much powder the cut contains. Almost no English-language writing explains this, and it is the main thing a buyer is actually choosing between.
Caffeine, stated and not quantified
All three contain caffeine and TeaHQ publishes no figure for any of them, because no source it holds carries the five-part basis a figure needs. Presence is a fact about the plant; a milligram number would be a claim about a cup nobody has measured.