Pterocarpus officinalis (Jack.) (Fabaceae) is the dominant tree species in the seasonally flooded swamp forests of Guadeloupe (Lesser Antilles). Here, we determined how P. officinalis seedlings and their symbionts were able to develop under waterlogging. A pot experiment was conducted to study the interactive effects of inoculation and waterlogging on nodulation, mycorrhizal colonization, nitrogen fixation, N contents in leaves and growth of P. officinalis seedlings. For this, they were inoculated at sowing with one strain of Bradyrhizobium sp. and/or with one arbuscular mycorrhizal fungus, Gloms infra radices, and watered near the field capacity until they were 3 weeks old. Then the half of the seedlings were waterlogged by marking up water level daily up to 3 cm above the soil surface. After 13 weeks of flooding, all flooded plants had developed adventitious roots and hypertrophied lenticels on the submerged part of the stem above the soil surface, and, however, grown better than non-flooded plants. In addition to their adaptation to flooding, the flooded plants formed true stem nodules, as they are connected vascularly to the stem, and arbuscular mycorrhizas on adventitious roots arising from the stem. Nodulatidn, nitrogen fixation, and N contents in leaves were not stimulated by flooding, whereas mycorrhizal colonization was. Mycorrhizal Pterocarpus seedlings adapted to flooding better than non-inoculated seedlings. This was achieved by the greater development of plant biomass. These results suggest that the adventitious roots and hypertrophied lenticels on stems are an important adaptation for flooding tolerance of P. officinalis seedlings, and probably contribute to the development of mycorrhizal colonization and plant growth. (Texte intégral)