Abstract
An account is given of a typical rainfed waterbody in the Al-Ammariyah Wadi (Saudi Arabia), with special reference to charophyte vegetation, water chemistry and topography of the area, which was studied from April 1996 to July 1997. Recurring patterns following rainfall and inundation of the waterbody are described as a model of temporal succession of biotic communities. Unispecific Chara braunii Gm. meadows were the first aquatic vegetation to emerge and overwhelmingly dominated the freshwater lentic ecosystem. This was followed by plankton and desert plants as the waterbody dried out. Chara braunii is reported as a new record for the Saudi Arabian charoflora. The species is characterised as stenohaline and tends to grow in vivo and in vitro in the salinity range of 0.2-0.8ppt. A gradual increase in elements and ions (Si 20-31 mg L super(-1) and pH 6.8-7.6) in the water was demonstrated as the waterbody desiccated. As a result of the increasing concentration of ions and pH, C. braunii developed heavy encrustation, and hastened fructification prior to desiccation of the waterbody between June and July 1997. Survival and emergence of C. braunii is positively correlated with drought resistant-oospores, specificity to hyposalinity, water-level fluctuations, and absence of herbivores.