Potamogeton illinoensis Morong

  • Authority

    Haynes, Robert R. & Holm-Nielsen, Lauritz B. 2003. Potamogetonaceae. Fl. Neotrop. Monogr. 85: 1-52. (Published by NYBG Press)

  • Family

    Potamogetonaceae

  • Scientific Name

    Potamogeton illinoensis Morong

  • Type

    Type. U.S.A. Illinois. Oquawka, H. N. Patterson s.n. (holotype, NY-n.v.).

  • Synonyms

    Potamogeton ziziiformis Hagstr., Potamogeton fragillimus Hagstr., Potamogeton pedersenii Tur, Potamogeton dunicola Tur, Potamogeton macrophylloides Hagstr., Potamogeton pulchelliformis Hagstr., Potamogeton lucens subsp. brasiliensis A.Benn. ex Asch. & Graebn.

  • Description

    Species Description - Rhizomes present; erect stems terete, without spots, 28-120 cm long. Leaves both submersed and floating or the floating absent, ± spirally arranged; submersed leaves sessile or petiolate, lax, entire to crisped, red-brown to light green, the blades elliptic to lanceolate or rarely linear, often arcuate, 7-19-veined, 5-20 x 0.2-4.5 cm, with 2-5 lacunae each side midrib, the apex noncucullate, acute-mucronate, the base acute, the glands absent, the petioles, if present, 0.5-4 cm long, the basal sheaths conspicuous, free from blade, nonligulate, light brown to red-brown, nonfibrous, not shredding at tip, 1-8 cm long, the apex acute; floating leaves petiolate, light green above, the blades elliptic to oblong-elliptic, 13-29-veined, 4-19 x 2-6.5 cm, the apex round-mucronate, the base cuneate, the petiole continuous in color to apex, 2-9 cm long. Turions absent. Inflorescences unbranched; peduncles similar, cylindric, terminal or axillary, erect to ascending, 4-30 cm long; spikes similar, cylindric, 2.5-7 cm long. Fruits sessile, laterally compressed, obovate to ovate, grayish green to olive-green, with well-developed abaxial keel and lateral ridges, 2.5-3.6 x 2.1-3 mm, the lateral ridges without points; beak erect to slightly recurved, 0.5-0.8 mm long; sides without basal tubercles; embryo with ca. one full spiral.

  • Discussion

    Ascherson and Graebner (1907) cited only Gardner 2756 in the protologue of Potamogeton lucens subsp. brasiliensis without stating from which herbarium the specimen(s) was/were examined. They make reference to the discussion by Bennett (1895). Here again, however, no particular herbarium is given. We have examined specimens from G, P, and US. All are the same taxon and are of equal quality. We are designating the specimen at P as the lectotype.

  • Distribution

    North America south to Mexico, West Indies, Central America, and South America. Alkaline waters of streams, rivers, lakes, ponds, and sloughs at elevations from near sea level to 2500 m.

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