Blunt-lobed woodsia (Woodsia obtusa) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific name:
Woodsia obtusa (Sprengel) Torrey subsp. obtusa
Synonyms:
Polypodium obtusum (Sprengel), Woodsia perriniana (Sprengel) Hooker & Greville
Common names:
Eng.: Blunt-lobed woodsia, Blunt-lobed cliff fern
Fr.: Woodsie à lobes arrondis, woodsie obtuse
Family:
Dryopteridaceae
Major plant group:
ferns

Morphological description

Blunt-lobed woodsia (Woodsia obtusa) is a small to medium-size fern with fronds up to 60 cm long and 15 cm wide (Figure 1). It is characterized by the blunt, rounded lobes of its bright green leaves, which are retained late into the fall.The leaf stalk (rachis) is straw-coloured, occasionally darker at base, not articulate but relatively brittle. The blade is coarsely cut and evidently 2-pinnate with proximal pinnules of lower pinnae usually shallowly lobed or merely dentate. In the field, blunt-lobed woodsia is most often confused with fragile fern (Cystopteris fragilis) but has a stiffer aspect, has glands and scales on the axes and veins as well as opaque stipes.

Figure 1. Blunt-lobed woodsia. a) plant growth form; b) leaf shape (Photographs: M. Wild).

Blunt-lobed woodsia. a) plant growth form; b) leaf shape

Genetic description

Blunt-lobed woodsia comprises two cytotypes that are often treated as subspecies because they show subtle morphological and ecological distinctions and tend to have different distributions. Tetraploid populations (subsp. obtusa) are found throughout the eastern part of its range, commonly occurring on limestone. The diploid (subsp. occidentalis) is found near the western edge of the species’ range, usually on sandstone and granitic substrates. It has been hypothesized that blunt-lobed woodsia might be an autopolyploid derived from W. oregana (Brown 1964). However, isozyme and spore ornamentation studies indicate that these species are not closely related, and the discovery of a diploid cytotype of blunt-lobed woodsia suggests a different origin for this taxon (Windham 1993). Blunt-lobed woodsia has been known to hybridize with W. oreganasubsp. cathcartiana (B.L. Robinson) Windham to form the sterile tetraploid hybrid known as W. × kansana Brooks (Windham 1993). 

Designatable units

There are no designatable units below the species level as only the subspecies Woodsia obtusa subsp. obtusa is found in Canada. All Canadian populations are located within the Great Lakes Plains Ecological Area as defined in the COSEWIC Operations and Procedures Manual and no significant genetic or morphological differences have been demonstrated for these populations.

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