Sagittaria graminea var. macrocarpa (J.G.Sm.) Bogin
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Authority
Bogin, Clifford. 1955. Revision of the genus Sagittaria (Alismataceae). Mem. New York Bot. Gard. 9 (2): 179-233.
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Family
Alismataceae
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Scientific Name
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Description
Species Description - Perennial with runners. Emersed leaves spatulate, 15-30 cm long, to 2 cm wide, the somewhat thickened phyllodia 15-25 cm long. Scape 15-30 cm long, with 2-4 whorls of flowers. Bracts moderately connate, ca. 0.4 cm long, the free ends triangular. Stamens (9-)12-18, the filaments ca. 1 mm long. Mature receptacle 0.8-1.2 cm in diameter; achenes large, 2.5-3.5 x 1.3-2 mm, the prominent dorsal wing crenate-crested, the faces plain or with 1-3 low ribs, the beak subulate, to 0.4 mm long, occasionally obsolete.
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Discussion
Sagittaria macrocarpa J.G.Sm. Missouri Bot. Gard. Rep. 6: 27. 1894.
Type collection: Curtis 'C', ponds, South Carolina (holotype MO; isotype GH). The type specimen unfortunately is not at all typical of the bulk of the collections, and indeed, comes very close to being intermediate between var. graminea and var. macrocarpa. The large crested achenes are distinctive, however, to serve safely to identify the type specimen and other intermediates as var. macrocarpa.
Sagittaria graminea is the only member of the genus with pubescent, dilated filaments. It apparently hybridizes with all other Sagittarias that have pubescent filaments and occur within its range, including S. rigida and S. lancifolia, both of which are closely related to it, and S. montevidensis from which it may have evolved.
In a genus characterized by variable species, S. graminea probably represents the high tide of that variability. Every characteristic is extremely plastic and it is the exception rather than the rule that enough variable factors become correlated in a geographic pattern to warrant the formation of a separate taxon. Altogether six varieties in addition to var. graminea are here recognized. All have been treated at one time or another as separate species, but careful study of some 1200 collections shows no basis for following this course. All these varieties fall entirely within the range of S. graminea var. graminea, but otherwise none of them ever encroaches on the geographic distribution of any other. Each shows some intergradation in its own range with var. graminea, and certain plants of similar appearance may occur in populations of var. graminea well removed from its accepted range. At the same time the extremes of these taxa are certainly distinctive and could not, except in a most juvenile state, be confused with var. graminea. Actually, then, the well-marked geographic isolates have been separated out as varieties, and the remainder included in var. graminea. The latter, therefore, is of necessity the most plastic variety and includes many incipiently variable plants as well as the numerous, intermediate forms.
The variety platyphylla of the Gulf and south-central states is easily recognized by the recurved pistillate pedicels. It probably arose as a result of hybridization between S. graminea and S. montevidensis subs p. calycina, with subsequent introgression with 5". graminea. It shows signs of being intermediate in bract, filament, and achene characteristics and has pistillate pedicels which resemble those of S. montevidensis. In all other respects it approaches S. graminea. A narrow-leaved form in Alabama has been called 5". mohrii but is not tenable as a taxon.
The var. teres of Cape Cod, Long Island, and the pine barrens of New Jersey shows differences that come close to being specific. The small, fully connate bracts, the crenate-winged achenes, and the peculiar spongy-terete phyllodia are all quite distinct.
The var. weatherbiana of the southeastern coastal plain is less distinctive. In general it is larger in all respects than var. graminea. Its unique production of leaves in the fall and the early spring flowering and fruiting make it seem worthy of separation.
The var. chapmani of Florida, Georgia, and Alabama is easily recognized by its elongate bracts, branching scapes, and small receptacles and achenes. Its mode of branching at times resembles that of some species of Alisma and Echinodorus, in that as many as five whorls may have the pedicels replaced by branches.
The var. macrocarpa of the Carolinas is distinguished mainly by the large, crenate-crested achenes and, to a lesser degree, by the spatulate leaf-shape. The var. cristatq of the northwestern Great Lakes region has a geographic distribution approaching that of a subspecies, for it has in large measure replaced var. graminea throughout its range. The short, basal phyllodia in association with the long-petioled, small-bladed emersed leaves, the large, crested achenes, and the filaments longer than the anthers are all distinctive.
The other previously proposed species here included in synonymy are probably ecological forms of S. graminea. They include the small, sterile, phyllodial plants of eastern, tidal waters (S. eatoni); the husky southern plants with horizontal rhizomes (5. cycloptera); the plants with tapering, terete phyllodes of southern lakes having a marked seasonal drop of water level (S. isoetiformis) and the elongate phyllodial plants of moving waters (S. edwardsiana). Another plant limited to the Cumberland plateau of northeastern Alabama is worthy of mention, although it has never been separated from S. graminea. It is unique in having elongate rhizomes that produce a series of phyllodia along their entire length in contrast to the typical apical crown of leaves. In general it resembles other flowing-water forms of S. graminea and pending further study has not been separated from that species. 5. lancifolia var. angustifolia of Grisebach is based on mixed collections of Wright in Cuba and in large part must be considered as S. graminea, although it is included in the synonymy of S. lancifolia as well.
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Distribution
North and South Carolina. A local plant of the highlands, but not the mountains, present in bogs, ponds, and sluggish streams. All the collections seen appear to be confined to Henderson Co., North Carolina and vicinity, except for the type collection which is labelled "South Carolina".
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