Trapa natans, L.

1. T. natans L. , Sp. Pl. 120 (1753) View Cited Treatment .

Annual, with unbranched stems 0-5-2 m. Submerged leaves caducous; floating leaves 1 -4-5 cm long and wide, usually rhombic, dentate, glabrous above, pubescent, at least on the veins, beneath; base broadly cuneate or almost truncate, entire; petiole up to 17 cm, pubescent,

often with a fusiform swelling. Flowers in the axils of the floating leaves; pedicels pubescent. Sepals narrowly triangular, keeled, accrescent and indurated in fruit, forming 2, 3 or 4 horns. Petals c. 8 mm, white, caducous. Nut 2-3-5 x 2-5-5 cm. 2n —c. 48. In nutrient-rich but not strongly calcareous water. S. & C. Europe, extending northwards to C. France and to c. 57° N. in C. Russia. Sometimes cultivated elsewhere, and formerly widespread in continental N. Europe, particularly during the Sub-boreal period. Al Au BI Bu Cz Ga Ge Gr He Hs Hu It Ju Po Rm Rs (B, C, W, K, E) fSu.

There is great variation in the size of the fruit and in the number and degree of development of the horns. Several of these variants have been described as species or subspecies, and populations in one lake or river-system may show considerable uniformity; there is, however, overlap in characters between populations. In addition some of the variation appears to be due to edaphic factors, such as abnormally high calcium or low potassium and nitrogen concentrations. It therefore seems unjustified to give taxonomic recognition to these populations.