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a leaf of fern or seed plants that develops one or more sporangia. The sporangia form in the axil of the leaf or on the leafs surface. In aquatic ferns microsporangia and megasporangia form in sporocarps on the same sporophyll. The sporophylls of heterosporous plants on which only microsporangia develop are called microsporophylls, and those on which only megasporangia develop are called megasporophylls. Microsporo phylls and megasporophylls are often more or less identical, for example, in heterosporous club mosses. In seed plants, however, they differ from one another and may be easily distinguished from assimilating leaves, or trophophylls.