Trapa natans
Trapa
water caltrop, water nut, water-chestnut
châtaigne d'eau, water chestnut, water chestnut or caltrop
slender, young growth and flowering parts velutinous.
submerged, flexible, unbranched, submerged nodes often developing green, pinnately-dissected to filiform adventitious leaflike roots.
of floating rosettes bearing successively longer petioles toward outer edges of rosette, to 20 cm;
blade 20–40 × 25–60 mm, width greater than length, surfaces velutinous abaxially, glabrous adaxially.
dimorphic, flanked by deeply cleft stipules; floating leaves alternately or spirally arranged in terminal rosette, supported by slender to bulbous float at mid petiole, blade rhombic to triangular, base cuneate, margins coarsely toothed in distal 1/2; submerged leaves subopposite, sessile, blade linear, margins entire.
indeterminate, emergent, solitary flowers in axils of floating leaves, pedicels elongating and declining after pollination, submerging developing fruit.
pedicellate, actinomorphic, monostylous;
floral tube perigynous to semi-epigynous, campanulate;
epicalyx segments absent;
sepals 4, 3 times floral tube length, persistent on fruit as hardened spines;
petals caducous, 4, white or pale lavender;
nectary development unknown;
stamens 4, in 1 whorl;
ovary 2-locular, surrounded by coronary disc, semi-inferior, fully inferior in fruit;
placenta axile, abbreviated, at apex of ovary;
style slender;
stigma capitate;
ovules 1 per locule, pendulous, 1 locule and ovule failing to develop after anthesis.
drupes, top-shaped, woody, with 2–4 hardened, spiny horns, endocarp indurate, exocarp evanescent, with tubercles.
20–25 mm diam., excluding spines;
horns 2–4, to ca. 10 mm.
1, oblong;
cotyledons 2, unequal, 1 large, starchy, retained in fruit, the other scalelike, growing out of fruit apex, becoming photosynthetic.
tube 2 mm;
sepals 4–7 mm, keeled;
petals obovate, 8–15 mm.
= 48 (Poland, Japan), 96 (Japan).
Trapa natans
Trapa
Trapa natans was first noted in Massachusetts in 1859 from an unknown origin and was recorded from the Charles River, Cambridge, in 1879. The hard, spiny fruits can cause severe puncture wounds and are slow to decay in lake and river bottoms. The species propagates by seed and by detached floating rosettes to form extensive floating mats that reduce oxygen, restrict light, crowd out native plants, and make navigation difficult. Populations grow rapidly and are difficult to eradicate except by sustained efforts over multiple seasons. Federal regulations now prohibit interstate sale and transport of T. natans. The species is considered rare and threatened in Europe.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species 1–30+ (1 in the flora).
Trapa is cultivated in China for the edible nut or enlarged cotyledon, which is referred to as water chestnut. The familiar cultivated Chinese water chestnut marketed in North America is usually another plant, the sedge Eleocharis dulcis (Burman f.) Trinius ex Henschel. Specialized features of Trapa (inflated leaf petioles, semi-inferior or fully inferior ovary, hardened horned fruits, unequal cotyledons) long made exact taxonomic placement difficult. Until recently, the genus was generally treated as the sole member of Trapaceae, with close relationship to Lythraceae or Onagraceae. Substantial molecular evidence indicates that Trapa is sister genus to Sonneratia Linnaeus f., a genus of mangrove trees in southeastern Asia. The two genera are well-nested within Lythraceae and closely related to two other Asian Lythraceae, Duabanga Buchanan-Hamilton, a genus of southeastern Asian trees, and Lagerstroemia, the crape myrtle (S. A. Graham et al. 2005). The great discrepancy in number of species attributed to the genus is primarily the result of extensive variability in the fruit shape and in the shape and number of horns and spines on the fruit. Trapa has become a notorious invader of rivers and lakes in the northeastern United States since its introduction in the nineteenth century. It was reported in southeastern Canada for the first time in 1998, extending the range northward from localities in the Lake Champlain watershed in the United States. Trapa fruits are well known from the Miocene, and younger, fossil deposits in the United States, Europe, and Asia.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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