1955] 



REVISION OF THE GENUS SAGITTARIA 



191 



Of the New World species, four cross the Tropic of Cancer (5. latifolia, S, lanci- 

 folia, S. graminea, S, longiloba), while one other (S, macrophylla) may be classi- 

 fied as semitropical. 



It Sagittaria rhombifolia Cham, Linnaea 10: 219. 1835. 

 Sagittaria af finis Seub. in Mart. Fl. Bras. 3(1): 111. 1847. 



Sagittaria lagoensis Seub. & Warm. Vidensk. Meddel. Naturh. Foren. Kjoeb. 1872: 113. 

 1872. 



Sagittaria rhomboidalis Micheli in DC. Monogr. Phan. 3: 66. 1881. Error for rhombifolia, 

 Sagittaria pugioniformis var. platyphylla Micheli in DC. Monogr. Phan. 3: 78. 1881. 

 Sagittaria pugioniformis var. affinis (Seub.) Kuntze, Rev. Gen. 3: 328. 1898. 

 Sagittaria pugioniformis var. rhombifolia (Cham.) Kuntze, Rev. Gen. 3: 328. 1898. 

 Sagittaria amazonica Huber, Bol. Mus. Goeldi 5: 314. 1909. 

 Sagittaria cordifolia Suess. & Beyerle, Repert. Sp. Nov. 39: 17. 1935. 

 Sagittaria pugioniformis Auct. non L. 



Perennial with horizontal rhizome. Leaves typically emersed, occasionally 

 submerged or floating, with linear to ovate blades 8-25 x 0.5-6 cm, the infrequent 

 floating blades cordate, the petioles 15-90 cm long or longer. Scapes simple, 

 20-90 cm long, with 3-10 whorls of flowers. Bracts large, 1.2-3 x 0.4-0.9 cm, 

 thickened, connate at the base, attenuate, those of the upper whorls somewhat 

 overlapping and appressed to scape. Pistillate flowers with pedicels strongly 

 recurved, markedly thickened, 1.5-4 cm long, occasionally with a ring of func- 

 tional stamens; sepals 1-2 x 1-2.5 cm, closely appressed to the receptacle at 

 maturity; petals 1.5-2.5 x 1-2 cm, all white or with a purple spot at the base. 

 Staminate flowers with pedicels filiform, divaricate, 2.5-8 cm long; stamens nu- 

 merous, the filaments linear, glabrous to minutely glandular-pubescent, 2-3 mm 

 long, the oblong anthers only 0.5-1.2 mm long. Mature pistillate heads 1.5-2.5 cm 

 in diameter; achenes large 2.5-5.5 x 1.3-2.5 mm, very narrowly winged, obovate, 

 abruptly tapering to a slender base, the faces unadorned, the beak 0.5-1 mm long, 

 horizontally or obliquely inserted. (FIG. 2a, b.) 



Type collection: Sellow s.n., Brazil (holotype not seen, presumably at Berlin; 

 i so type K). 



Distribution: Lowlands of tropical South America. Collections examined from 

 Bolivia, British Guiana, Brazil, Colombia, Paraguay, Venezuela. (FIG. 2.) 



A widespread but seldom collected tropical species of shallow waters of lakes, 

 swamps, and quiet waterways. The wide variation in leaf outline is seemingly the 

 only basis for the proposed synonyms. The thickened, recurved pedicels, the 

 closely appressed sepals, the occasional rings of functional stamens in the pistil- 

 late flowers, and the purely tropical distribution serve to relate 5. rhombifolia 

 most closely with S, montevidensis and S. guyanensis. The species superficially 

 resembles S, montevidensis subsp. chilensis; however, the overlapping, appressed 

 bracts, the large, unadorned achenes, the non-sagittate leaves and the geographical 

 distribution are all quite distinct. 



All authors since Linnaeus have ascribed this species to S. pugioniformis L. 

 Close examination of a photograph of the Linnaean type specimen of S, pugioni- 

 formis shows that it has no relation to S, rhombifolia except for the similarly 

 narrowed leaves. The Linnaean type is obviously the narrow-leaves form of S, 

 lancifolia L. (5. angustifolia Lindl.), showing the typical reflexed sepals and 

 ascending pedicels of the pistillate flowers of the subgenus Sagittaria. 



Explanation of Figure 2 



FIG. 2. Distribution of some South American species of Sagittaria, a, b, S. rhombi- 

 folia, a, bracts, X 2 / 3 . b, achene, X 3. c, d, S. sprucei, c, bracts, X 2 / 3 . d, achene, X 3. 

 e, f, S. montevidensis subsp. montevidensis, e, bracts and pistillate flower, X %, f, 

 achene, X 3. g; bracts and pistillate flower of S, montevidensis subsp. chilensis, X %. 



