Patterns of biomass allocation were investigated in two species of Lycopus with different modes of vegetative extension. L. americanus produces belowground rhizomes, whereas L. uniflorus produces surface stolons with attached tubers. Individuals of both species were harvested in 1985 and 1986 from two habitats in northern Michigan (marsh and floodplain) where they co-occur. Seasonal patterns of allocation, year-to-year, site-to-site, and interspecific differences in sexual reproduction effort (SRE) and vegetative reproductive effort (VRE) were examined. In both species, SRE was greatest in the marsh, whereas VRE was greatest in the floodplain. Results from a reciprocal transplant experiment made between the marsh and floodplain, to quantify the degree to which the observed site-to-site differences in SRE and VRE are environmentally or genetically determined, will be presented.