Leptosporangiate fern
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Leptosporangiate ferns are vascular spore plants, whose sporangia arose from a single epidermal cell and not from a group of cells as in eusporangiate ferns. The sporangia are typically covered with a scale (from Greek: 'lepis', 'lepidos') called the indusium, which can cover the whole sorus, but can also be strongly reduced. Many leptosporangiate ferns have an annulus around the sporanium, which ejects the spores.
Most extant fern families are leptosporangiates. Examples are: Dryopteridaceae, Cyatheaceae, Polypodiaceae, Athyriaceae, Woodsiaceae, Onocleaceae, Lomariopsidaceae and Tectariaceae.
References:
Smith, A. R., Pryer, K. M., Schuettpelz, E., Korall, P., Schneider, H., Wolf, P. 2006. A classification for extant ferns. Taxon 55(3): 705-731.
Sporne, K. R. 1962. The morphology of pteridophytes, the structure of ferns and allied plants. pp. 127-135. Hutchison & Co. London.