Myers, C. V., R. C. Anderson, and D. L. Byers (Behavior, Ecology, Evolution, and Systematics Section, 4120 Department of Biological Sciences, Illinois State University, Normal, IL 61790-4120). Influence of shading on the growth and leaf photosynthesis of the invasive non-indigenous plant garlic mustard [Alliaria petiolata (M. Bieb) Cavara and Grande] grown under simulated late-winter to mid-spring conditions. J. Torrey Bot. Soc. 132: 1–10. 2005.—Plasticity in photosynthetic response to varied light conditions likely contributes to the successful spread and domination of eastern deciduous forest ground layers by the invasive, non-indigenous plant species Alliaria petiolata. We examined the effects of growing plants with no shading, or under 30% or 60% black shade cloth on leaf photosynthetic rates, maximum rates of leaf photosynthesis (A_max) and stomatal conductance (g_Smax), light compensation point, above and below ground biomass, chlorophyll content and specific leaf mass of A. petiolata grown under simulated late-winter to mid-spring conditions of temperature, photoperiod, and irradiance in a growth chamber. The 0% shade treatment plants exhibited a significantly greater leaf photosynthetic rate than the 60% shade treatment plants between 800 and 1600 μmol·m⁻²·s⁻¹ photosynthetically active photon flux density (PPFD). Leaf A_max was significantly greater for plants grown under no shade than for plants grown under either the 30 or 60% shade treatments and g_Smax was higher for plants grown under no shade than plants in the 60% shade treatment. Plants grown under 0 and 30% shade produced significantly more biomass and had greater specific leaf mass than plants grown under 60% shade. Leaves of the 60% shade treatment had significantly greater chlorophyll a and b content than leaves of the 0 and 30% shade treatments. Our results indicate that A. petiolata displays a plastic response to varied light levels in a way that would likely increase its success in invading eastern deciduous forest ground layers.