Organisms that experience changing environments often respond by making physiological and morphological modifications that may affect their survival and reproduction. While phenotypic responses (plasticity) to temporal variation are probably common, research on phenotypic plasticity has primarily focused on spatial variation, and few studies examine phenotypic responses of individuals to changing environments. We conducted field and lab experiments designed to test the assumptions and predictions of models that analyze the fitness consequences of plasticity for hybrid genotypes in Piriqueta caroliniana growing in environments with varying levels of temporal predictability. In field experiments the plasticity of several leaf traits including area (shift to smaller leaves), width/length ratio (shift to narrower leaves), and trichome density (shift to higher density) had significant effects on final plant size (P<0.01) in a temporally variable field environment (28 days of mesic conditions followed by 28 days of drought).  In greenhouse experiments the same set of genotypes were grown for two months with wet and dry treatments alternating at frequencies of D (duration of constant environment) = 8, 16, 24, and 48 days.  For plasticity in leaf trichome density, genotypes with the greatest increase in response to drought attained the largest size when the duration of drought was longest (D=48).  This advantage diminished as D declined and there was no apparent advantage of plasticity when D=8. These results follow the outcomes of models for modular organisms growing in variable environments with the exception that an advantage of plasticity was observed at shorter periods of fluctuation (D) than predicted.