Which instrument is characterized as being a Mexican upright tubular drum opened at the bottom?

The instrument that is characterized as a Mexican upright tubular drum opened at the bottom is the Huehueti. This drum is traditionally made from a hollowed-out tree trunk and is significant in many indigenous Mexican cultures, often used in ceremonies and rituals. The structure allows for a deep, resonant sound, which is essential in various musical and cultural expressions.

The Huehueti is specifically played vertically and is often associated with the Aztec culture. Its contribution to rhythmic patterns in traditional music makes it a vital instrument for maintaining the cultural heritage of Mexico.

The other options do represent important aspects of Mexican music but are distinct from the characteristics of the Huehueti. The Teponaztli is also a type of drum but has different construction and sound qualities. Zampoñas refer to a type of pan flute, which is entirely a different category of instrument, while Mariachi is a music genre that often includes various instruments but does not denote a specific instrument itself.