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Natural rubber is an essential material, especially for plane and truck tyres but also for medical gloves. Asia ranks first in the production of natural rubber, of which the Hevea tree is currently the sole source. However, it is anticipated that this source alone will not be able to fulfill the growing demand. Guayule, a shrub native to northern Mexico and southern United States, may also contribute. This plant not only contains polyisoprene, but also resin, a mixture of lipids and terpenoids. This review summarizes various aspects of this plant, from the usage history, botanical description, geographical distribution and cultivation practices, down to polyisoprene and resin biosynthesis including their distribution within the plant and molecular composition. Finally, the main processes yielding dry rubber or latex are depicted, as well as the properties of the various extracts along with economic considerations. The aim is to provide a wide picture of current knowledge available about this promising crop, a good feedstock candidate for a multiple-product biorefinery.

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a b s t r a c t Natural rubber demand was 11 million tons in 2014 and is expected to reach 16 million tons by 2025 according to the International Rubber Study Group (IRSG). The expected limitation of natural rubber from Hevea induced an interest for the development of alternative sources of natural rubber. Guayule (Parthenium argentatum Gray L.), being native to the Mexican Chihuahua desert, is a perennial crop of semi-arid area, with the potential of growing in the Mediterranean area. To assess the potential of guayule cultivation, CIRAD (France) and Wageningen University (The Netherlands) have conducted some on-farm guayule trials in southern Europe in partnership within the European based production and exploitation of alternative rubber and latex sources project (EU-PEARLS). Promising agronomic results have led to assess the profitability of a guayule commodity chain in the Mediterranean Europe area. Data on farming practices, biorefinery, costs of inputs were collected from the trials conducted in Spain and France, and from farmers and farmers' organizations in both countries. At farm level, different cost scenarios were tested, with guayule biomass being the sole output, with annual or biennial harvests. Our results showed that, based on a nine-year field cultivation, the farmer's breakeven point can be reached at a sale price of D 147 ton −1 of dry biomass (at 12 ton ha −1 ). At factory level, the biorefiner needs to sell water-extracted rubber as latex. By adding solvent extraction, it is possible to extract the remaining percentage of total rubber and the resin. In such case, the biorefiner's profits rises to D 691 ton −1 of extracted rubber, making guayule cultivation profitable. Bagasse sale for electricity production or wood pellets is a bonus to be considered too. Our results showed that, in these conditions, a guayule value chain in Europe could be profitable.We extrapolated the results from our experiments to other Mediterranean countrie's culture conditions. Our results showed that guayule cultivation would probably be more beneficial in the Southern Mediterranean countries, including Spain, than in the Northern countries (South of France). Introduction of guayule production in the Mediterranean region could contribute to improved sustainability in rural development projects, allow a new economic development of the regions, and contribute to provide a new sustainable crop alternative against the impacts of climate change such as longer and more severe drought stress.