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Guayule (Parthenium argentatum Gray, Asteraceae) grows wild in the arid and semi-arid regions in Mexico and represents a potential source of natural rubber and latex. Evaluation of guayule’s natural distribution allows identification and selection of high yielding accessions from these sites. Our objective was to inventory different native stands of guayule in Mexico to assess their usefulness for research and development by measuring plant density, spatial distribution patterns, biomass, rubber and resin content and other morphological characteristics during a 3-year-period in three native stands. The study sites were: Norias de Guadalupe (Zacatecas), Rocamontes (Zacatecas), and Gomez Farias (Coahuila), with work carried out from January 1999 to February 2002. Plant density was evaluated by the point-centered quarter method, and spatial distribution pattern was estimated using the block quadrant variance method. Whole plants for analysis were collected once a month from small, medium, and large sizes at each site. During the three years of study the highest number of small plants was observed in Rocamontes (23,000 small plants ha(-1)). The lowest number of small plants (1007 plants ha(-1)) and the highest number of dead plants (6200 plants ha(-1)) were observed in Norias de Guadalupe. In Gomez Farias, plant development was intermediate between the two other sites. The spatial distribution pattern of guayule plants in the sites was not clear as no clump (plant aggregates) was observed. The factor analysis showed positive correlation among height, main stein and first branch diameter, dry weight, and plant width. These parameters were negatively correlated with the sampling year. The rubber and resin content showed a negative correlation with moisture content. (c) 2004 Elsevier B.V. All rights reserved.