Isoetes riparia Englem. ex A. Braun var. canadensis Engelm. ex N.E. Pfeiff.
Habitat: Margins of lakes, ponds, and streams. Tidal shores or estuaries. Circumneutral or slightly acidic, oligotrophic waters.
Range: Labrador, Ontario, and Quebec south to South Carolina
Aids to Identification: Quillworts are recognized by their rosettes of ascending basal leaves in aquatic environments. Identification of quillworts is difficult and is based on characteristics of the microscopic megaspores that are found enclosed in the swollen base of the basal leaves. Shore quillwort has bright green, evergreen, twisted and often spirally arranged leaves that become paler towards the base. The megaspores have an obscure girdle.
Ecological characteristics: The only known occurrence of this species occurred on the sandy bottom of a pond in several meters of water.
Phenology: Spores mature in late summer.
Synonyms: Isoetes canadesis (Engelm) A.A. Eat. ex Maxon, Nom. illeg.
Known Distribution in Maine: This rare plant has been documented from a total of 1 towns in the following counties: Oxford.
Reason(s) for rarity: At northern limit of range.
Conservation considerations: Unknown; has not been seen in Maine in over 30 years.