The autecology of Battarrea stevenii in ephemeral rivers of southwestern Africa

In September 1990, 74 sporocarps of Battarrea stevenii were observed on the floodplain of the ephemeral Kuiseb River in western Namibia. Herein we rep ort subsequent studies of the distribution, abundance, nutritional role, ph enology, and sporocarp development of this fungus in the hyper-arid Namib D esert. Included are full descriptions of developing and mature sporocarps. B. stevenii is a common associate of riparian forests on silty floodplain t erraces, but does not form mycorrhizal associations with the dominant woody species, Faidherbia albida or Tamarix usneoides. Rather, clamped mycelium extends throughout floodplain soils decomposing coarse and fine particulate organic material (4-7% of soil dry weight). Sporocarp production occurs 4. 5-12 mo post-flooding in response to soil desiccation at depths of 20-35 cm . The extensive mycelium, duration of vegetative growth post-flooding, and large size and abundance of B. stevenii sporocarps suggest that it is an im portant component of the subsurface decomposer community in the Namib's eph emeral rivers. Given that the fungus has also been recorded from floodplain soils of Angola, Hungary, and New Mexico (U.S.A.), and is known to have a world-wide distribution, we predict that further biogeographical studies wi ll reveal that B. stevenii is a characteristic element of the riparian biot a in dryland rivers, which drain approximately one-third of the earth's lan d surface.