Published online by Cambridge University Press: 12 June 2017
Spurred anoda and velvetleaf were grown for 40 days in controlled-environment chambers in monocultures at densities of 2, 4, 8, and 12 plants per 20-cm-diam pot and in mixed culture with all combinations of 2, 4, 8, and 12 plants of each species per pot. The day/night temperature was 29/23 C, and the photosynthetic photon flux density (PPFD) was 1000 μE m–2 s–1. Shoot dry weights and leaf areas of the two species were similar when they were grown in monoculture. However, in mixed culture spurred anoda exceeded velvetleaf in leaf area/plant and shoot weight/plant in 15 out of 16 treatments. Multiple linear regression equations relating shoot biomass/plant to the density of both species in mixed culture were calculated. Comparison of competition coefficients from these equations indicated that the competitive impact of a single spurred anoda plant was equivalent to the impact of 2.5 velvetleaf plants. In mixed culture, spurred anoda always contributed a greater proportion of the total shoot weight and total leaf area per pot than would be predicted from its proportion of the total plant population. These results indicate spurred anoda is competitively superior to velvetleaf.