leptosporangiate

RADIATION AND DIVERSIFICATION OF LEPTOSPORANGIATE FERNS

According to Schuettpelz and Pryer (2009), leptosporangiate ferns originated near the start of the Carboniferous period (359.

Many leptosporangiate groups are known to evolve via reticulate evolution and to form cryptic complexes, involving all of the cited processes as hybridization, polyploidy and apogamy.

The remaining living ferns consist of heterosporous leptosporangiate genera that are either amphibious (Marsileales) or floating aquatics (Salviniales; Gifford & Foster, 1989).

These include 13 extant homosporous filicaleans, 17 extinct homosporous and heterosporous ferns from Paleozoic strata, five extant and one extinct heterosporous leptosporangiate ferns, two extant marattiaceous ferns, two extant ophioglossaceous ferns, one extant and two extinct equisetophytes, both extant homosporous psilotophytes (i.

Ophioglossales) as sister group to the eusporangiate marattialean ferns plus the leptosporangiate ferns.

Most leptosporangiate ferns share a common shoot apical organizational pattern, in which a superficial layer of large anticlinally elongate cells overlies a zone of smaller isodiametric cells.

Although the basic structure of the shoot apical meristem seems to be similar for leptosporangiate ferns, the terminology and concepts used by different authors to characterize the apical zonation has varied.

Aspects of the later development of the leaf in leptosporangiate ferns have been investigated by relatively few recent workers.