Plants large to very large, occasionally smaller, turgid, variegated red and green, brownish red, blackish red, or sometimes green throughout. Stems sparsely and irregularly branched, shoot apices sometimes hooked. Stem leaves often with red pigment present in large parts of leaf or sometimes only in transverse sub-basal zone, broadly ovate, concave or strongly so, plicate or not, 0.8–2 mm wide; base patent, distinctly constricted at insertion; apex acute or acuminate.
Habitat: Wet, mesotrophic, often spring-influenced mires, lakeshores, submerged in lakes
Elevation: low to moderate elevations (0-1100 m)
Alta., Yukon, Alaska, n Eurasia.
Hamatocaulis lapponicus is rare in western parts of the flora area. The species is recognized by its large size (approximately as large as Scorpidium scorpioides), usually slightly plicate stem leaves without differentiated alar cells, and stem with neither central strand nor hyalodermis. Besides the larger size, H. lapponicus differs from H. vernicosus in its more or less patent stem leaf bases, and in stem leaves broadly ovate and more distinctly constricted at their insertion. Hamatocaulis lapponicus is usually more sparsely and irregularly branched than H. vernicosus, has somewhat less plicate leaves, and large parts of its shoots are more often red.