TWO ECOTYPES OF IRIS ATROFUSCA BAK. AND THEIR RELATIONS TO MAN-MODIFIED HABITATS

ABSTRACT Iris atrofusca Bak. occurs in two different habitats in the northern Negev: (1) deep loessial soils of the 'Arad valley which have been under primitive cultivation for thousands of years and (2) shallow loessial lithosols in the hills north of Be'er Sheva which have been under heavy grazing pressure. In this latter habitat, Asphodelus microcarpus, an unpalatable geophyte, has become the dominant species. The plants of I. atrofusca in the 'Arad valley have markedly curved (falcate) leaves, whereas those of the Be'er Sheva hills have erect (ensiform) leaves and their overall habitus is very similar to that of A. microcarpus. It is hypothesized that this latter ecotype has evolved as a result of natural selection under grazing pressure, whereby the erect-leaved plants survived because of their visual similarity to the unpalatable species.

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