In recent years, collecting in Mexico without an official permit is forbidden, and represents a serious violation of the law penalized with jail. The rules for scientific collections in Mexico were published in the Nom-126-Ecol-2000, in the official Mexican journal.
If you plan to collect in Mexico, check your rights and obligations. This is specially true in some States of the country, where people is aware of the responsibility of taking care of the natural resources and has been trained to request and recognize official permits. The state of Oaxaca is such a case!
Therefore, if you are planning to collect plants or animals while you are visiting, make sure that you have a contact in Mexico that has a permit and is willing to collaborate with you or request one for yourself. Requesting a collecting permit requires time and money, so plan in advance! Foreigners collecting in Mexico require a permit from the Foreigner Affairs Office and from SEMARNAT.