Studies on vegetative production of Potamogeton illinoensis Morong in southern Argentina

Potamogeton illinoensis Morong is a major submerged weed invading irrigation channels in the Lower Valley of the Río Negro, near Viedma, Argentina. Studies on morphology and growth characteristics of this species were conducted in an outdoor tank from August 1993 to May 1994 with the objective of increasing the knowledge of its ecology order to adjust control measures. The maximum aboveground biomass was reached in April, with a subsequent decrease to May when the water supply was cut off. Belowground biomass comprised two kinds of rhizomes. The first group (Rhizomes I) was produced from the beginning of the annual cycle causing both lateral shoots and new rhizomes I production. The second group (Rhizomes II) was distinguished as an enlargement of the extremes of rhizomes I from mid-November, producing only short overwintering sprouts. Plant parts production (DW in g/plant) in the first cycle was: 27.2 g leaves; 11.9 g stems; 17.4 g rhizomes I and 8.1 g rhizomes II. Vegetative propagation appeared to be an important survival strategy in this species. During the 3–4 month period without water only rhizomes with underground overwintering sprouts survive in the dry sediment.