In this paper, we present high-resolution, contiguous plant macrofossil records taken from two glacial cirque mountain wetland ecosystems located in the subalpine zone of the Eastern Carpathians. We provide 1) a detailed reconstruction of plant succession from mountain peatland ecosystems; 2) a possible scenario of Holocene paleohydrological changes; 3) the presence of rare plants presently considered glacial relicts, e.g. Meesia triquetra; and 4) the peat forming potential of certain plants at altitudes above 1800 m a.s.l. At Gărgălău, a gradual decrease of water level and isolation from ground water influence approximately 7000 cal yr BP trigged the colonization of minerotrophic Sphagnum species (S. teres, S. centrale and S. subsecundum). The decline of Sphagnum subsecundum ca. 3000 cal yr BP was most likely caused by an increase of water level and competiton with Sarmentypnum sarmentosum populations. In the Late Holocene, ca. 2000 cal yr BP, Selaginella selaginoides expansion was recorded, followed by the reappearance of Sphagnum populations, most likely due to a lowering of the water table. The Gropile ecosystem transformed from a shallow lake into peatland at ca. 4200 cal yr BP. The temporary presence of Warnstorfia exannulata in peat sediments ca. 2300, 1600, 1300–1200, and 700–600 cal yr BP may indicate an increase of water level and very wet habitat, or the presence of small ponds. Paleohydrological changes only partly agree at both studied wetlands, suggesting the importance of local climatic and morphological conditions on past vegetation development. According to our paleoecological data, Straminergon stramineum indicates wet stages in peatlands and cannot be considered a high peat-forming species in subalpine zones in European mountain ranges. Projected warm and dry conditions may trigger mountain peatland water tables in Eastern Carpathians to decline, potentially resulting in the expansion of moss species that demand more acidic and drier habitats, e.g. Sphagnum russowii.