Isoetes acadiensis Kott
Habitat: Submersed in ponds or lakes, less often in rivers, rooted in gravel, sand, or mud, rarely amphibious [Open water (non-forested, wetland)].
Range: Nova Scotia and New Brunswick south to Massachussetts. Common in Nova Scotia.
Aids to Identification: The various quillwort species can be difficult to identify because they are often distinguished by microscopic differences of the reproductive macro spores. The typical form of the quillworts is a dense rosette of narrow leaves with the spores located inside the widened leaf bases. I. acadiensis has 9-35 leaves, mostly curved backward, 5-21 cm long, and typically dark green. The megaspores are about 0.5 mm wide with a loose network of smooth, rounded ridges (vs. irregular roughened crests in I. tuckermanii).
Ecological characteristics:Generally associated with acidic water (pH 5.0-5.3).
Phenology: Perennial; megaspores mature in August and September.
Synonyms: Widely considered a legitimate taxon, but Gleason & Cronquist (Second ed., 1991) did not segregate from the more common Isoetes tuckermanii A. Braun ex Engelm.
Known Distribution in Maine: This rare plant has been documented from a total of 3 town(s) in the following county(ies): Aroostook, Hancock.
Dates of documented observations are: 1898, 1917, 1995
Reason(s) for rarity: Restricted range.
Conservation considerations: Maintain hydrologic integrity and water quality of pond habitat.