Recente vondsten van Callitriche palustris L. (Klein sterrenkroos) in Nederland

Callitriche palustris is very rare in the Netherlands. The last recent records were from 1953 and 1979. Therefore it is quite remarkable that in 1999 and 2000 C. palustris was found at several locations by independent observers: 1. Poached clay overlying sandy soils along the river Vecht which flooded during extremely high water; 2. Ditches in low-lying parts of a clay polder. The ditches are probably fed by a combination of precipitation and inflow from the river Rhine; 3. The dried up bank of an oxbow of the river IJssel, in riparian grassland under intensive agriculture; 4. Silt exposed after spring flooding on the edge of the IJsselmeer; 5. The sandy margin of a lake in the floodplain of the river Waal. The authors suggest that these recent records do not indicate a range expansion by C. palustris. It appears more likely that the increase in number of records is due to an increasing number of botanists actively recording aquatic plants and particularly increased recording of Callitriche species. The records in 1999 seem to coincide with high-water levels in the river Rhine during the preceding spring. The article provides additional information on the diagnosis of the species (incl. a line drawing of the fruits).