Fens are characterized as shallow water bodies permanently or periodically flooded by ground-water table, originating from the percolation of rain water through mineral soils of uplands adjacent to the fen central basin. Fens have organic soil and their plant cover is dominat by emergent phanerophytes. This study aims to survey the specific diversity and characterize the main vegetation types along two 200m transects positioned in a fen of the southern Brazilian county of Domingos Petrolini (32° 02' S; 52° 17' W; Rio Grande, RS). In March/1998, 48 plant species (30 families) were recorded in forty 5m × 2m plots along the two transects. Herbaceous aquatic macrophytes (submersed, flooting or emergent) represented 56% of species, but 10% were shrubs or trees. Seven species dominate the vegetation (Eupatorium tremulum, Eryngium pandanifolium, Blechnum brasiliense, Rhynchospora sp., Xyris jupicai, Utricularia gibba, and Cladium jamaicense). The vegetation types include (1) summer exposed swampsdominated by Cladium jamaicense (placed in the fen central basin; FCB), (2) intermediate level of Gravatás/Caraguatás (Eryngium pandanifolium) associated with the fern Blechnum brasiliense (+0.5 to +1.5m from the FCB), (3) marginal palustrine shrubs (+1 to +3m from the FCB) dominated by Eupatorium tremulum and (4) turf fields covered by small sedges, soft-leaved grasses with the yellow-eyed grass (Xyris jupicai) occupying the upper border of the fen (+3 to +4m from the FCB).
fen; Cladium; Blechnum; Eupatorium; vegetation
