(Last Modified On 12/18/2012)
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(Last Modified On 12/18/2012)
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Species
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ROTALA MEXICANA Cham. & Schlechtd.
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PlaceOfPublication
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Linnaea 5:567. 1830.
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Synonym
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Rotala pusilla Tul. in Ann. Sci. Nat. 4 ser. 6:128. 1856. Rotala apetala F. Muell. Fragm. 3:108. 1862. Hypobrichia spruceana var. tenuifolia Griseb. Cat. P1. Cub. 106. 1866. Ammannia pygmea S. Kurz, in Seem. Journ. Bot. 5:376. 1867. Rotala verticillaris Hiern, in Oliv. Fl. Trop. Afr. 2:467. 1871. Rotala mexicana , spruceana Hiern, loc. cit. 1871. Rotala mexicana subsp. typica var. a forma minima Koehne, in Mart. Fl. Bras. 132:195. 1877. Rotala mexicana subsp. typica var. a forma media Koehne, loc. cit. 1877. Rotala mexicana subsp. typica var. a forma major Koehne, loc. cit. 1877. Rotala -mexicana subsp. typica var. spruceana (Griseb.) Koehne, loc. cit. 1877. Rotala mexicana subsp. typica Koehne, in Engl. Bot. Jahrb. 1: 151. 18 8 0. Rotala mexicana subsp. hierniana Koehne, loc. cit. 1880. Rotala mexicana subsp. typica var. chamissoana-Koehne, in Engl. Pflanzenr. 4:30. 1903. Rotala mexicana subsp. pusilla (Tul.) Koehne, loc. cit. 1903.
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Description
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Creeping aquatic or palustrine herbs to 3 dm. tall, the branches obscurely angular. Leaves ternate, the submerged leaves linear, 3-18 mm. long, 0.5-3.0 mm. wide, the emersed leaves 3-8 mm. long, 1-2 mm. wide, both obtuse or retuse, cuneate-attenuate at the base. Flowers sessile, subtended by 2 setose bracteoles. Hypanthium urceolate, 0.6-1.0 mm. long, 0.5-0.6 mm. broad at the orifice; calyx lobes narrowly deltoid, sometimes unequal. Petals absent. Stamens commonly 2, the anthers oblong-ovoid, about 0.1 mm. long, 0.25 mm. wide, the filaments about 0.4 mm. long. Ovary globose, abruptly narrowed into a short gynophore, 0.4 mm. long; style about 0.1 mm. long. Seeds suborbicular, about 0.3 mm. long, 0.25 mm. wide.
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Habit
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herbs
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Distribution
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Central and South America, Asia, Africa and Australia. Found at low eleva- tions in periodic streams and potholes.
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Specimen
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CANAL ZONE: along the old Las Cruces Trail, between Fort Clayton and Corozal, Standley 29222; Darien Station, Standley 3I539. CHIRIQUI: lower portion of valley and marshes along Rio Ant-on, El Valle de Anto6n, about 500 m., Hunter d Allen 366. PANAMA: near Matias Hernandez, Standley 28989; near the big swamp east of the Rio Tecumen, Standley 267I5; vicinity of Juan Franco Race Track, near Panama', Standley 27817; along road between Panama' and Chepo, Dodge, Hunter, Steyermarkl, d Allen I672I; Las Sabanas, Bro. Heriberto i5I; San Jose Island, Perlas Archipelago, East Harbor, Johnston 83o, Erlanson 459.
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Note
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Since this species is often found in periodic waters, two habits are found: an emersed and a submerged. Rotala mexicana flowers when the plants become emersed. Considerable difficulty is encountered in attempting to identify the submerged specimens. Identification, by means of vegetative characters only, is best accomplished by use of the obtuse or retuse leaf apex character.
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