Morphological variation in rosette-forming plants (Hesperoyucca, Asparagaceae) along a latitudinal gradient of dry environments in the Baja California Peninsula.

Morphological variation provides plants the potential to respond to heterogeneous environmental pressures. Species with restricted distributions in dry habitats are particularly interesting because small-scale environmental gradients may influence trait variation. We evaluated morphological variation in two rosette-forming Hesperoyucca species, H. whipplei and H. peninsularis, across a latitudinal gradient in the Baja California Peninsula (BCP) and identified the environmental variables most strongly associated with morphological traits. We measured 15 morphological traits in 181 adult plants from 22 sites along the BCP. Multivariate analyses (PCA, MANOVA, linear mixed models and ANCOVA) were used to assess variation within and between species and to test associations with latitude and environmental variables. Morphological variation showed clear species-level differentiation, with significant differences in tepal size, overall plant size and architectural traits. At the regional scale, morphological variation was significantly associated with latitude. Tepal size and plant architecture covaried with solar radiation and precipitation, respectively, indicating that morphological traits covary with environmental heterogeneity across the BCP. Morphological variation in Hesperoyucca varies along the latitudinal gradient of the BCP and differs between species. Despite their restricted distributions, both species exhibit geographical trait variation associated with local environmental conditions. These findings highlight the role of environmental heterogeneity in shaping morphological patterns at regional scales and provide a baseline for future genetic and experimental studies.