Flora of the Southeastern United States
2022 Edition


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Isoetes Linnaeus. Quillwort, Merlin's-grass.

Contributed by P.W. Schafran, L.J. Musselman, and A.S. Weakley

Key to Isoetes

A genus of about 250-300 species, cosmopolitan in distribution. Allopolyploids, derived from crossing between parental species and genome duplication, represent roughly half of the named taxa in eastern North America. Molecular data suggest that many of the southeastern polyploid species contain complexes of morphologically similar but genetically unique taxa. These complexes represent independent polyploidy events between different sets of parental species. The appropriate systematic treatment of these complexes would recognize approximately twice as many species. At present, many polyploid species should be treated only as taxonomic, not evolutionary, entities.

ID notes: Hybrids are possible between many combinations of species. Hybrids are readily recognized by having megaspores of variable size, shape, and ornamentation (aborted). Leaf width measurements are at midpoint of the leaf length, well above the flared base. Leaf lengths are of undamaged leaves from leaf tip to the top of the rootstock.

Ref: Boom (1982); Bray, Schafran, & Musselman (2018); Brunton (2015); Brunton (2016); Brunton & Britton (1996a); Brunton & Britton (1996b); Brunton & Britton (1997); Brunton & Britton (1998); Brunton & Britton (1999); Brunton & McNeill (2015); Caplen & Werth (2000a); Caplen & Werth (2000b); Hoot, Napier, & Taylor (2004); Jermy In Kramer & Green (1990); Kott & Britton (1983); Luebke & Budke (2003); Musselman (2001); Musselman & Knepper (1994); Musselman et al. (1995); Musselman, Bray, & Knepper (1996); Musselman, Bray, & Knepper (1997); Musselman, Taylor, & Bray (2001); Schafran (2019); Schafran et al. (2016); Schafran et al. (2018); Singhurst et al. (2011); Taylor et al. (1993a) In Flora of North America Editorial Committee (1993b); Wood et al. (2020a). Show full citations.

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image of plant© Alan Cressler: Isoetes piedmontana, Cedar Mountain, Douglas County, Georgia 1 by Alan Cressler source
image of plant© Alan Cressler: Isoetes lacustris, Piseco Lake, Little Sand Point State Campground, Adirondack Park, Hamilton County, New York 3 by Alan Cressler source