Abstract
The morphology of plants of Polygonum spectabile (Polygonaceae) from the "várzea" of the Rio
Solimões is compared for periods of drought and flooding. During the period of flooding, the plants
showed: 1) higher values of length and diameter of the internodes and nodes, when compared with plants
of the dry period, and 2) aerenchyma in emersed and submersed internodes close to the water surface. The
presence of this aerenchyma and the internal characteristics of the plant (i.e. absence of medulla) indicate
a continuous vertical flow of oxygen in the stem, which might be sufficient to supply submersed organs,
during flooding, when the concentration of this gas in the water may be close to zero. The aerenchyma
could, also, help buoyancy of the plants, keeping their leaves and flowers emersed.
