Temporarily flooded forests (TFF’s) are among the most endangered tree communities in Southeast Mexico and in a contradictory way among the least known in terms of their diversity. Therefore, the aim of this study was to characterize the richness, diversity (Shannon-Wiener) and dominance (relative importance value; RIV) of a TFF of the Yucatan Peninsula, and evaluate its floristic affinities with other TFF’s and upland forests (UF’s) of Southeast Mexico. A sampling method based on 10 quadrants of 10 x 20 m (2 000 m2) was used to record all woody individuals with diameter ≥ 1 cm and height ≥ 1.5 m. A floristic similarity analysis was used including 192 genera of woody plants belonging to TFF’s and UF’s of the Yucatan and Tabasco TFF’s. A Mantel correlation test was performed to determine if the geographic distance has effect on the floristic similarities between TFF’s and UF´s of the Yucatan peninsula. The TFF under study was characterized with a low level of diversity (2.79) and species richness (56), and a high dominance level (52.3 % of RIV in five species). Dominant species such as Haematoxylum campechianum, Dalbergia glabra, Cameraria latifolia, Byrsonima crassifolia, Crescentia cujete and Terminalia buceras showed a floristic neotropical affinity typical of floodable habitats. The structure of the community was characterized by an inverted "J" pattern for the distribution of individuals in the diametric and height classes. The high density of woody lianas, mainly of Dalbergia glabra (22 % of the recorded individuals) suggested an optimal state of conservation of the studied area. The floristic similarity analysis revealed that most of TFF’s in Yucatan Peninsula were grouped with high similarity (55 %) independently of the adjacent UF’s; however, TFF´s resulted similar among them (36 % similarity) when compared with TFF’s from other regions (16 % similarity). According to the Mantel test, the similarity between sites is not influenced by its geographical proximity (r = -0.098, p>0.05). This emphasizes the need to generate conservation strategies for the TFF's of the Yucatan peninsula independently from other regions of Southeast Mexico. Our results suggest that the TFF of the studied region has a similar diversity from other TFF’s in Southeast Mexico, a different floristic composition compared with adjacent UF’s and a structure with an optimal conservation status, characteristics that indicate their importance for the regional flora conservation. Further ecological studies are needed to build a solid foundation for management and conservation for the TFF’s.

Keywords: Low inundated forest, Yucatan peninsula, wetland, plant diversity, floristic relationships, Haematoxylum campechianum.