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lant can alter their development, physiology and life history depending on environmental conditions. This fundamental property is called phenotypic plasticity. The North American lake cress, Rorippa aquatica is an herbaceous perennial aquatic mustard. Typical habitat of lake cress is at shores of ponds, slow-moving streams and other quiet waters in North America. The lake cress shows heterophylly, phenotypic plasticity on leaf shape. In nature, the leaf shape of this plant depends on whether the plant is submerged in or emergent from water (Fig. 1). Submerged leaves are usually deeply dissected and has needle-like blade, whereas emergent leaves are generally entire with serrated or smooth margins. This phenotypic plasticity on leaf shape is thought to be adaptive response to submergence and increase the fitness in water's edge environment where most of lake cress populations are found. Interestingly, the leaf shape changes in response to varying temperature and light intensity, as well as to underwater submergence