Growth, reproduction and resource allocation of <i>Tithonia diversifolia</i> and <i>Tithonia rotundifolia</i>

Abstract

Summary Growth, reproduction and resource allocation of the polycarpic Tithonia diversifolia and the monocarpic Tithonia rotundifolia were studied in mixed and monoculture populations. The aim was to identify the characteristics contributing to the invasive habits of these species. Tithonia rotundifolia attained reproductive maturity at 2 months and T. diversifolia 4 months after planting . Tithonia rotundifolia completed its life cycle after 4 months, just as T. diversifolia was starting to flower. Both plant species produced a high number of seeds per capitulum (136–144 seeds in T. diversifolia ; 113–120 in T. rotundifolia ). Tithonia diversifolia reproduced asexually and sexually and produced many small light seeds . Tithonia rotundifolia produced large seeds, had early rapid growth, short life cycle and high reproductive effort. Growth in mixture did not significantly affect plant height, numbers of branches and leaves, or leaf size, but affected biomass allocation to reproductive and vegetative activities in the species. The attributes contributing to the invasiveness of these species are large seeds, early rapid growth, short life cycle and high reproductive effort in T. rotundifolia , with many small light seeds and asexual and sexual reproduction in T. diversifolia . For both species, control of recruitment would be a means of limiting their invasiveness.