Gradients of physical conditions and biological interactions of species may generate assembly patterns of trait-convergence and trait-divergence in the structure of plant communities. Here we report evidence on the effect of canopy closure on non-random patterns in the functional structure of herbaceous plant communities in temperate forest. We evaluated SLA (specific leaf area), leaf area and shape, dry matter content, presence of rhizomes, and plant height and inclination. In one of the three sites surveyed we found clear patterns of both trait-convergence and trait-divergence. Along the canopy closure gradient we observed communities formed by species with large SLA and long and narrow leaves being replaced by communities formed by species with smaller SLA and rounded leaves, which we interpret as environmental filtering producing such a trait-convergence. Further, communities located in more open sites contained more distinct species in terms of SLA, leaf area and leaf shape, i.e., indicating a divergence pattern along the canopy closure gradient. The other study sites showed no significant patterns when analyzed alone. When the three sites were analyzed jointly, a significant pattern of convergence for plant inclination was found. Although subjected to local variation and historical agents, our study presents consistent patterns of both trait-convergence and divergence and evidence of assembly rules and non-random patterns in communities of herbaceous plants along a canopy closure gradient.