Pak. J. Bot., 44: 407-411, Special Issue March 2012. OXALIS CORNICULATA AS A SUCCESSFUL LAWN WEED: A STUDY OF MORPHOLOGICAL VARIATION FROM CONTRASTING HABITATS MUHAMMAD IBRAHIM MALIK, SEEMA MAHMOOD * , GHULAM YASIN AND NAHIDAH BASHIR Institute of Pure and Applied Biology, Bahauddin Zakariya University, Multan Pakistan * Corresponding author’s e-mail: drseema pk@gmail.com Abstract Oxalis corniculata, an abnoxious weed and is of cosmopolitan distribution. The species is a successful invader and seems to be adapted to a wide array of habitats. In the present study various survival strategies of the species under different environmental conditions were assessed through the variability of morphological character expressions. Eight populations of the O. corniculta were sampled from 4 contrasting habitats and were studied for various traits. The populations exhibited distinct morphological responses with respect to changing environmental conditions. The variability of phenotypic expressions seems to provide some selective advantage for survival under contrasting habitat situations. The species appeared to be a successful lawn weed as the maximum adaptive significance of character expressions was observed from a mowed lawn. The study suggested that various abiotic/ biotic factors did not limit the growth of the species. Hence, chemical control seems to be an appropriate strategy for weed management. Introduction The term ‘weed’ is used for a number of species that are invasive plants of natural and agricultural ecosystems (Charudattan, 2005). Weeds are regarded as a nuisance because they are unwanted plant species. Weeds interfere with human land use as they are successful colonizers and have considerable impact on plant growth (Garbari & Pedulla, 2001). Weeds also cause problems for water management as they impede flow of water through irrigation ditches. Weeds are well adapted to highly unstable and unpredictable environments as they can compete with plants for nutrients, water, light, space, and harbor crop pests or diseases through different survival tactics (Rodenburg et al., 2010). Morphological variation leads to different survival strategies has long been recognized because it enables the plants to acclimatize in changing habitats (Gambino & Vilela, 2011). Phenotypic variability is a reflection of the genetic constitution of the individuals and their interaction with the environment. Thus, morphological expressions are usually pertinent to habitat conditions (Jaleel et al., 2008; Mandák et al., 2011). Hence, plant populations occupy and are maintained in diverse habitats through the adjustment of morphological expressions (Urbas & Zobel, 2000). O. corniculata or creeping wood-sorrel, or yellow wood-sorrel is of cosmopolitan distribution and is considered as a troublesome weed that successfully grows in lawns, arable lands, waste places and gardens. It tends to become especially troublesome in pots growing in greenhouses (Anon., 2000). Although, the traditional approach to study weeds is to examine their control or management (Rodenburg et al., 2010) but the main goal of weed management is to understand the way by which weeds exist? Therefore, in the present study several populations of O. corniculata were studied from contrasting habitats. These provenances were examined for various phenotypic expressions to understand the survival strategies and successful invasion of the weed in a wide range of habitat. Thus, the main objectives of the study were to reveal population differentiation in O. corniculata from contrasting environments as well as to explore the variability of morphological expressions that provide some selective advantage to the species for its maintenance in a variety of habitat. Materials and Methods Choice of sites: Several sites at Bahauddin Zakariya University Multan, Pakistan (30°11N and 71°28E) were visited to observe natural growing populations of O. corniculata. The species was found growing under different environmental conditions. Four contrasting habitats (8 sites) were selected for sampling. The sampling details are summarized in Table 1. Table 1. Habitats types and description of the sites selected for sampling of populations of Oxalis corniculata. S. No. Habitats Description 1. Sun An open area with maximum exposure to sun light, high temperature, rain fed area. 2. Shade With thick canopy of Accacia nilotica, Morus nigra and Eucalyptus lanceolatum with greater amount of litter. 3. Irrigated area Along a water course, highly moist soil. 4. Derelict/ Dry land Dry sandy soil, rain fed area with harsh set of environmental conditions. 5. Neighboring with grasses Lawn of Botanic Garden with different grass species Poa annua, Dicanthium annulatum, Polypogon monspeliensis, Cyprus rotendus, Cynodon dactylon, competition for space, water, light nutrients etc. 6. Neighboring with Shrubs Growing in competition with Shrubs like Dodonia viscosa, Rosa indica, Hibiscus rosasinensis, Nerium oleander. Soil sandy loam, competition for water and nutrients, low light intensity due to shade of shrubs. 7. Mowed Lawn A well maintained lawn. Regular mowing with ample watering. 8. Unmowed site Flower beds of a lawn with some annual ornamental plants such as Bellis perennis, Helianthus annuus, Petunia alba, Lathyrus odoratus and Tagetes erecta.