Re: Trapa natans L.

Common Names: Water Chestnut, Bull Nut

Family: Onagraceae (evening primrose family) or Trapaceae (a discrete 
monogenerous family). Dicotyledonous.

Habit: Plants floating, usually rooted in the mud, with leaves clustered 
toward the tip of the stem, forming a rosette. Stem long and lax, rather 
more elongated than in other rosette species. Amphibious, can produce 
land forms on wet mud substrates. Floating leaves four-sided with long 
petioles which have an inflated spongy region. Submersed leaves opposite, 
finely dissected ... or ... In the lower part of the stem are numerous 
finely branched adventitious roots. Theophrastus, the Father of Botany 
(b. 370 BC) stated that, " quite peculiar to this plant is the hair-like 
character of the growths which spring from the stalk; for these are 
neither leaves nor stalk." The exact nature of the finely branched 
submerged structures has been a topic for debate for quite some time! The 
upper 'roots' contain chlorophyll and the lower 'roots' can anchor the 
plant in shallow water where there is a muddy substrate. Flowers aerial, 
white, solitary, axillary among floating leaves, entomophilous (insect 
pollinated). Ovary two-chambered. After fertilization, peduncles curve 
downward, fruit develops submerged. Fruit a nut-like caltrop, four-horned 
with four sharp barbed spines, large, fleshy, edible. Unlike most aquatic 
plants, it is an annual therophyte (overwinters as seed). Seed germinates 
in substrate, firmly anchored by lateral roots.

Uses: Fruits form a staple food in continental Asia, Malaysia and India. 
Used especially in Chinese dishes. Several countries in southeast Asia, 
and also Chinese communities in Europe and North America, import the 
fruit directly from China. Fruits are used in the preparation of 
liniments to treat elephantiasis, pestilent fevers, rheumatism, sores, 
sunburn and skin complaints. Used also as food for pigs and other 
livestock in southeast Asia. 
In 1981, Germany issued a set of four stamps of aquatic plants, one of 
which was Trapa natans. The others were Lobelia dortmanna, Caltha 
palustris and 'Water Gillyflower' (whatever that is).

Distribution: Paleotropical and warm temperate Eurasian. Introduced in 
North America. Agnes Arber (Water Plants, 1920) wrote " ... the present 
distribution of certain aquatics cannot be understood unless allowance be 
made for the influence of mankind in their dispersal. Trapa natans ... is 
an instance. This plant now occurs over a considerable part of Europe, 
the Caucusus and Siberia. It has been used from early times for food, 
medicine and magic, and is supposed to have been introduced into 
Switzerland as long ago as the period of the lake dwellings. It is now 
nearly exterminated in that country, and has vanished from various 
localities in Belgium, Holland and Sweden ... It certainly seems to be a 
plant which is in process of extinction in various parts of its range ..."

Introduced from Eurasia into North America in approximately 1874. 
Initially cultured in Asa Gray's botanical garden at Harvard University 
in 1877. By 1879 it had escaped into local waters. Locally abundant in 
the Atlantic States, sometimes forming large floating mats. This species 
has become a noxious weed in the waters where it has become established. 
It is an interesting paradox that it is considered a rare and endangered 
species in many parts of its 'native' habitat yet a noxious weed in North 
America. Dave Whittaker recently mentioned that it is in fact a 
restricted species in Canada. Withing its natural North American range, 
it is found in waters of pH 6.7 to 8.2, with alkalinity from 12 to 128 
mg/l CaCO3.

Well, you asked Karen ...
Dr. dave