Remains of Euryale ferox nuts (seeds in botanical terminology) at GBY were identified by their characteristic features such as the prominent longitudinal ridge (raphe), shape and location of the operculum and hilum, as well as the structure of the seed surfaces (Figures 1, 3). These characteristics distinguish Euryale ferox from related fossil genera such as Palaeoeuryale and Pseudoeuryale (Miki 1960).
The prickly water-lily is an annual or perennial plant with long-petiole leaves whose large rounded blades (normally up to 1.3 and occasionally 2.4m in diameter) float on the water surface. The long petiole and veins that protrude from the bottom of the blade are densely covered with sharp prickles. The rhizome is sunk deep in the ground with the help of groups of thick and fleshy roots. The plant develops approximately 15–20 spongy fruits, each of which contains 30–40 nuts. When the fruit is ripe it dehisces and releases the nuts, which are covered by a mucilaginous arillus (Jha et al. 1991).
The plant grows in shallow stagnant water generally 0.3–1.5m deep and at a neutral pH. In the study region in Madhubani District, Bihar, water depths reach a maximum depth of around 3.5m. Flowering occurs in April–May and the fruits ripen and dehisce between June and August, when spherical nuts are released. The nuts have a mucilaginous arillus that holds them above the water surface for several days, after which they sink to the bottom of the water body. The plant germinates in early winter and grows with surprising speed, the biomass doubling each month from January to July. The maximal biomass found in a pond in India was 1.7kg/m² fresh weight in July. Temperature has a profound effect on the rate of biomass production (Jha et al. 1991).
As regards their nutritional value, E. ferox nuts contain 12.8% moisture, 9.7% protein, 0.1% fat, 0.5% minerals, 76.9% carbohydrates, 0.9% phosphorus, 0.02% calcium and 1.4 mg/100g carotene. The calorific value is 362 kcal/100g for raw E. ferox and 328 kcal/100g for popped nuts (see below for description of the processing techniques of these nuts). Popped nuts are comparable with staple food such as wheat and rice. The essential amino acid indices (EAAI) in the raw and popped parts of edible E. ferox nuts are 93% and 89%, respectively. These are higher than the values for rice (83%), wheat (65%), Bengal grain (81.55%), soya bean (85.6%), amaranth (57.5%), human milk (81.55%), cow's milk (88.8%), fish (89.2%) and mutton (87.24%) (Jha et al. 1991; Jha and Barat 2003; Ghosh and Santra 2003). E. ferox nuts are superior to dry fruits such as almonds, walnuts, coconuts and cashew nuts in terms of sugar, protein, ascorbic acid and phenol content (Jha et al. 1991; Jha and Barat 2003; Ghosh and Santra 2003).
E. ferox was present in Europe in the geological past, becoming extinct during the Quaternary (Simpson 1936; Miki 1960; Soboleweska 1970; Jha et al. 1991; Ghosh and Santra 2003). Fossil nuts of this species have been reported from the Pleistocene in Poland (Soboleweska 1970) and England (Gibbard et al. 1996), and from the Oligocene in Scotland (Simpson 1936). Evidence of E. ferox is also noted in Tertiary deposits in Kolkata, India (Jha et al. 1991; Ghosh and Santra 2003). Nuts of several extinct fossil Euryale species, including E. europaea Weber, E. lissa Reid and E. nodulosa Reid, were found in geological layers in Europe and Japan (Miki 1960). At present, E. ferox is the only surviving species of the genus, which is the only recent genus of the subfamily Euryaloideae.