Subsection XI. Totally Aquatic and Usually Fully Submerged Pondweeds

compiled by Dave Richardson

1a. Leaves thread-like, pointed, alternate, distinctly flattened in cross-section with one vein; stem white or green, up to 1.5 m. long; seeds black; generally in submerged beds or exposed mats on marsh surface.....Widgeon Grass, Ruppia maritima (RPPMRT).
1b. Leaves ribbon-like, with roundish tips; plant upright or nearly so in deep water, trailing under or on the surface in shallow water, sometimes exposed on mudbanks at low tide; seeds half-hidden in a long row in leaf sheaths.....Eelgrass, Zostera marina (ZSTMRN).