ST. LOUIS - Four of the world's leading botanical institutions are working on a catalogue of every plant in the world, with plans to make the inventory of at least 400,000 species available for free online by 2020.

Those involved in the project say at least 100,000 plant species worldwide are threatened by extinction.

Plans for the catalogue called the World Flora were announced Monday by the St. Louis-based Missouri Botanical Garden, New York Botanical Garden and two British institutions, the Royal Botanic Garden Edinburgh and Royal Botanic Gardens, Kew.

The catalogue will include scientific information and images for every known species, with new ones added as they are discovered.

Officials at the botanical organizations say developing the catalogue is partly aimed at helping halt the loss of plant biodiversity around the world.

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