DIVERSITY OF STEM NODULATION SITES IN AESCHYNOMENE SPP

Fourteen species of Aeschynomene [A. afraspera, A. nilotica, A. indica, A. ciliata, A. denticulata, A. evnia, A. pratensis, A. rudis, A. scabra, A. sensitiva, A. tambacoundensis, A. elaphroxylon, A. pfundii, and A. crassicaulis] growing in waterlogged soils of Western Africa develop nodules on both stems and roots. Stem nodules are formed at predetermined sites called nodulation sites, which always include a lateral root primordium. Aeschynomene species fall into three groups according to the anatomy of their nodulation sites: a) In the most evolved nodulation site, the root primordium breaks through the epidermal dome (e.g. A. afraspera). b) In the least evolved nodulation site, the root primordium remains embedded in the cortical tissues of the stem (e.g. A. elaphroxylon). c) In an intermediate type of nodulation site, the apex of the root primordium is overlayed with intact epidermal cells (e.g. A. indica). The frequency of stem nodulation is related to the accessibility of the root primordium for rhizobia.