I don't know what kind of gourd it is *specifically*, but a couple of days ago I saw one listed on Ebay as just a Mate Gourd. I think that's it's name though, but I'm not sure.

Charlie

Yerba maté is a herbal green tea grown in South America. It is drunk using a maté gourd and a bombilla straw.

Yerba maté is the drink, the gourd is the traditional vessel. Sometimes the "mate gourd" isn't even a real gourd, it's glass or wood, even embellished with silver or gold. Traditionally, yerba maté was infused and served in real gourds, but these days, people collect them, and they can be made out of nearly anything. They get incredibly elaborate as well, and vary in cost depending on the degree of rarity and workmanship.

As for what sort of gourd is used (when a gourd is used) from all the ones I've seen it looks like large egg gourds are used.