Marsilea drummondii is a species of fern known by the common name nardoo. It is native to Australia, where it is widespread and common, particularly in inland regions. It is a rhizomatous perennial aquatic fern that roots in mud substrates and produces herbage that floats on the surface of quiet water bodies. It occurs in water up to one meter deep.
It occurs in abundance after floods and can form mats on the water's surface covering the ground in carpets as floodwaters recede. It is variable in appearance and occurs in many types of wetland habitats. In general the frond is made up of two pairs of leaflets and is borne erect when not floating. The plant produces sporocarps which can remain viable for 50 years and only release spores after being thoroughly soaked. The sporocarps are dispersed by birds that eat them but cannot digest them, and also spread by flowing water. Sporocarps are hard, woody structures about 0.5-1 cm long that are produced on stalks that arise from the rhizome. They bear sori, which are the structures in which the fern spores are produced.
The sporocarp is used for food by Australian Aborigines, who collect and grind them to powder which they mix with water to make a dough. The sporocarp can be toxic due to high levels of thiaminase, which destroys thiamine (vitamin of B1). Consumption of large amounts of nardoo can cause beriberi. It has been known to poison sheep, as well as humans, including the leaders of the Burke and Wills expedition. Nardoo must be prepared properly before consumption to destroy the thiaminase.
Burke and Wills ground the sporocarps dry, then cooked the flour in much the same way that wheat and barley are ground and cooked. This method of preparation contrasted with that used by the Aborigines, who ground them with water to make a thin paste. As nardoo sporocarps contain large amounts of the enzyme thiaminase, mixing the flour with water stops the enzyme's action and also dilutes the other chemicals that are needed for the enzyme to destroy thiamine. In their preparation method, the Aborigines did not allow the watery paste to come into contact with bark or leaf utensils. Had they used bark or leaf, amino acids from them could have activated the thiaminase.
This post is part of the Friday Greens meme,
and also part of the Food Friday meme,
and also part of Pippa's Week That Has Been Friday meme.