Seed size in lacustrine and riverine populations of wild rice in northern minnesota and wisconsin

Anecdotal information gathered from contemporary wild rice harvesters, traditional ecological knowledge of indigenous peoples, and biologists suggests that seeds produced by wild rice (Zizania palustris L.) in riverine habitats are smaller than those produced in lacustrine habitats. To study the differences in the seed size of wild rice between lakes and rivers, four river and four lake pairs were sampled to measure and model the factors affecting seed size. We found mean seed mass to be quantitatively different between lacustrine and riverine environments; seed mass in lake populations was (41%) larger than that in river populations. When partitioned between water body type, regional population pairs, and individual populations, water body type accounted for 71.3% of the variance. Data collected on seed mass, plant morphology, sediment characteristics, and water depths were used to create a statistical model to quantify the effects of each factor on seed size. The two most important environmental factors contributing to seed size were sediment bulk density and water depth at seed collection. Important biological components were seed scar density, proportion of filled seed, and root biomass.