Seasonal changes in aboveground and belowground standing crop and primary production in aCarex lacustriswetland were determined and related to the basic life history of this species. There was a seasonal minimum of 180 g/m2green material aboveground frozen in the ice in winter and a maximum of 1037 g/m2in summer (early August). Seasonal aboveground production based on quadrat data and based on the difference between maximum and minimum standing crop is estimated to be 857 g/m2per year, maximum daily production 15 g/m2per day. A second estimate, also based on quadrat data but taking into account the very high shoot mortality during the growing season, was determined. Seasonal aboveground production then is 1580 g/m2per year, maximum daily production is 20.3 g/m2per day. Belowground standing crop was 387 g/m2in winter but then declined to an average summer low of 226 g/m2. Belowground standing crop increased during autumn and, by October 7, a value equal to the previous winter's value was reached. Shoots of this species live for 1 year or less, emerging in autumn, overwintering, and then dying sometime during the next summer.