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.

Interference between redstem filaree and round-leaved mallow was studied under controlled environmental conditions. Each species was grown in monoculture at densities of 2, 4, 8, and 12 plants per 20-cm-diam pot and in mixtures at all possible combinations of these densities. Leaf area per plant was similar for both species but round-leaved mallow grew taller and produced more shoot biomass than redstem filaree when each was grown in monoculture. Mixed culture responses varied with the proportion density of each species. A reciprocal yield model was tested and modified to account for this significant density interaction. When grown in mixture, round-leaved mallow usually gained in leaf area and shoot biomass at the expense of redstem filaree indicating that it was the superior competitor. Calculated competition ratios indicate that round-leaved mallow was about twice as competitive as redstem filaree under the growing conditions of this study.