Distribution, Habitats, and Taxonomy of Ruppia maritima L. and R. occidentalis S. Watson in Nebraska

Specimens of Ruppia from all eleven Nebraska counties in which it is known fall into two groups: R. occidentalis in alkaline Sandhills waters and R. maritima in saline waters of the Platte River Valley and Lancaster County. Ruppia occidentalis is distinguished by its more robust size; redspotted leaves and stems; terete, entire, obtuse leaves; 4-8(9) carpels; and by two elliptic white spots on its endocarp, among other characteristics. Ruppia maritima is more delicate and unspotted; the leaves are oblate in section, sub-apically denticulate, and acute-acuminate; the carpels are 3 or 4, and the endocarp spots are nearly circular. Both species grow in waters of low species-richness of submersed macrophytes; Potamogeton pectinatus often grows with them in Nebraska, and Chara sp., Myriophyllum sp., Utricularia vulgaris, and Zannichellia palustris are sometimes present. Water qualities of some lakes having Ruppia are summarized.