Pellaea glabella
Introduction '''''Pellaea glabella''''' is a fern with the common name '''smooth cliffbrake'''. It was once regarded as a reduced form or variety of ''Pellaea atropurpurea''. ''P. glabella'' is known to exist in two cryptic species, one diploid and one tetraploid. The diploid reproduces sexually, while the tetraploid is normally apogamous. It is now known that the tetraploid form of the species is one of the parents of the original hybrid ''P.'' × ''atropurpurea'' that became the apogamous species.
Range and Habitat ''P. glabella'' ranges widely in the United States and much of Canada, excluding the northernmost regions and Alaska. ''P. glabella'' is epipetric, normally growing on well-weathered limestone, usually in cracks with little or no soil. It can also be found on sandstone and basalt, probably in places where calcium is locally concentrated. It favors more exposed sites than ''P. atropurpurea''.
Description This species has sessile or nearly sessile pinnae. Sori are formed on the underside of the pinnae edges and are covered by a false indusium formed by curled under pinna edges. It can be distinguished from ''Pellaea atropurpurea'' by its smooth, not hairy, stipe and rachis (the main leaf stalk and stem).
Taxonomy ''P. glabella'' has been assigned a total of four subspecies:* ''Pellaea glabella'' subsp. ''glabella'' Mettenius ex Kuhn* ''Pellaea glabella'' subsp. ''missouriensis'' (G. J. Gastony) Windham* ''Pellaea glabella'' subsp. ''occidentalis'' (E. E. Nelson) Windham* ''Pellaea glabella'' subsp. ''simplex'' (Butters) A. Löve & D. LöveThe subspecies ''glabella'' and ''simplex'' are the tetraploids, while ''missouriensis'' and ''occidentalis'' are the diploids. ''Glabella'' and ''missouriensis'' have hairlike scales near the midrib, while ''simplex'' and ''occidentalis'' are completely glabrous.
References *''P. glabella'' USDA Plants Profile: http://plants.usda.gov/java/profile?symbol=PEGL*''P. glabella'' in '''Flora of North America''': http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500875