J. Bio. & Env. Sci. 2012 26 | Musyimi et al. RESEARCH PAPER OPEN ACCESS Allelopathic effects of Mexican sunflower [Tithonia diversifolia (Hemsl) A. Gray] on germination and growth of Spiderplant (Cleome gynandra L.) D. M. Musyimi * , S. W. Kahihu, D. K. Buyela, P. A. Sikuku Department of Botany, Faculty of Science, Maseno University, P.O BOX, 333, Maseno, Kenya Received: 16 July 2012 Revised: 04 August 2012 Accepted: 06 August 2012 Key words: Allelopathy, growth, spiderplant, leaf extracts, Maseno University. Abstract Allelopathy refers to both beneficial and harmful effects of one plant on another plant by the release of chemicals from plant parts through leaching, root exudation, volatilization, residue decomposition and other processes in both natural and agricultural systems. Tithonia diversifolia contains allelochemicals that inhibit or stimulate growth of agricultural crops. A study was conducted to investigate the allelopathic effects of fresh shoot aqueous extracts of T. diversifolia on the germination of seeds and growth of young seedlings of Spiderplant (Cleome gynandra) under laboratory and glasshouse conditions. Seeds of C. gynandra were germinated in sterilized petri-dishes lined with two layers of whatman no.1 filter papers moistened with 10ml of fresh shoot aqueous extracts of T. diversifolia (0%, 25%, 50%, 75%, and 100%) in Department of Botany laboratory of Maseno University. Number of seeds germinating each day was recorded and germination percentage calculated for each treatment at the end of the experiment. Plumule and radicle lengths were also measured. In the glasshouse, individual plants were grown in 4.5 litre plastic pots containing soil. The treatments allocated to the pots involved 4 different concentrations: 400ml aqueous shoot extracts of T. diversifolia at 25%, 50%, 75% and 100% and tap water (control). The treatments were replicated five times and the pots laid out in a completely randomized design. The fresh shoot aqueous extracts of T. diversifolia did not show significant (p > 0.05) allelopathic effect on germination of seeds of C. gynandra. However, higher shoot extracts concentration stimulated the germination of the seeds. Plumule and radicle lengths were significantly (p < 0.05) inhibited by higher concentrations of the shoot extracts. The aqueous shoot extracts of T. diversifolia significantly stimulated shoot height, leaf area, number of leaves, fresh weight and dry weight of C. gynandra. The study indicated that aqueous fresh shoot extracts of T. diversifolia have both stimulatory and inhibitory effects on spiderplant (C. gynandra,) germination and growth. * Corresponding Author: D.M. Musyimi  davidmusyimi2002@yahoo.com Journal of Biodiversity and Environmental Sciences (JBES) ISSN: 2220-6663 (Print) 2222-3045 (Online) Vol. 2, No. 8, p. 26-35, 2012 http://www.innspub.net