The plants - dudhi (Euphorbia hirta), black nightshade (Solanum nigrum), and chhotagokhuru (Tribulus terrestris) - are used to treat conditions including worm infestation, stomach irritation, menstrual pain and urinary infections.
In the US, Proctor & Gamble, Phytopharm and Zeneca have registered patents covering various uses of general extracts and specific chemicals from the plants. They include "pharmaceutical compositions for the treatment of skin disorders" and "for gastro-protection". These would include the ways Indians now use the plants, or their extracts.
The Gaia Foundation pressure group condemned the move as "prospecting for green gold", in which companies hope to patent medicines used for centuries by Indian practitioners. But Richard Dixey, chief executive of Huntingdon-based Phytopharm, accused the group of "flag-waving" and India of sabre-rattling.
"We use Tribulus as a component of a formulation that comes from China," he said. "India is trying to lay claim to ownership of plants that are distributed all over the Far East. But Tribulus is one of 10 components of our own product which we source in China. We buy tonnes of it - earning that country very good money."
Patenting plants and indigenous naturally occurring chemicals has become increasingly contentious. Biotechnology companies say patents are necessary to protect the investment made to discover the active chemicals or genes, and that the patents only cover specified applications of those discoveries. They also point out that patents are public, and have a limited lifespan.
Vandana Shiva, of the Indian Research Foundation for Science, Technology and Ecology said: "Since all these plants' properties have been systematically studied within our indigenous knowledge systems ... claims to novelty, on which the patents are based, are false."Reuse content