Chara braunii (Charales, Charophyta) in an arid rainfed waterbody, Saudi Arabia

An account is given of a typical rainfed waterbody in the Al-Ammariyah Wadi (Saudi Arabia), with special reference to charophyte vegetation, water che mistry and topography of the area, which was studied from April 1996 to Jul y 1997. Recurring patterns following rainfall and inundation of the waterbo dy are described as a model of temporal succession of biotic communities. U nispecific Chara braunii Gm. meadows were the first aquatic vegetation to e merge and overwhelmingly dominated the freshwater lentic ecosystem. This wa s 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 s pecies is characterised as stenohaline and tends to grow in vivo and in vit ro in the salinity range of 0.2-0.8 parts per thousand. A gradual increase in elements and ions (Si 20-31 mg L-1 and pH 6.8-7.6) in the water was demo nstrated as the waterbody desiccated. As a result of the increasing concent ration of ions and pH, C. braunii developed heavy encrustation, and hastene d fructification prior to desiccation of the waterbody between June and Jul y 1997. Survival and emergence of C. braunii is positively correlated with drought resistant-oospores, specificity to hyposalinity, water-level fluctu ations, and absence of herbivores.