The study was based on an intensive program of collection from July 2006 to May
2010 throughout the state of the Rio Grande do Norte: 21 field expeditions along Apodi–Mossor river (supported by the project Petrobrás Ambiental/rio Apodi-Mossoró), one expedition to the middle West and Seridó regions, one to the
Low Açu valley, one to the Agreste Potiguar, and three to the East Littoral region. In addition, it was analyzed the specimen collections deposited in the herbaria EAC, HUEFS, MOSS, UB, UFRN and UFP (abbreviations according to Thiers [continuously updated]). The descriptions of the character states followed Radford et al. (1974)