Background:

In arid regions, palm groves function as wetland refugia, supporting hydrophytic plant communities under extreme climatic constraints. Despite their ecological significance, the regional patterns of these assemblages remain poorly understood.

Questions:

We asked whether the composition of hydrophytic plant communities across arid palm groves in the Baja California Peninsula and southern California reflects regional climatic gradients, and hypothesized that differentiation is structured by climate-driven variation.

Data:

We compiled a database of 1,133 plant species (including 368 hydrophytes) associated with the five native palms, using herbarium records and literature sources. Analyses focused on species classified as aquatic, subaquatic, or tolerant.

Study site and dates:

Data encompass 235 palm groves spanning a 1,400 km climatic gradient across the Baja California Peninsula (Mexico) to California (USA). Records range from 1950 to 2022.

Methods:

Species composition was analyzed across 18 areas using non-metric multidimensional scaling ordination, species vector fitting, and distance-based redundancy analysis with 19 bioclimatic variables from WorldClim.

Results:

We recorded 368 wetland-associated species: 252 tolerant, 79 subaquatic, and 37 aquatic species. Ordination revealed strong floristic structuring along a latitudinal gradient, distinguishing tropical southern areas from Mediterranean northern ones; distance-based redundancy analysis showed climate explained 55 % of variation, with precipitation during the driest quarter as a key predictor.

Conclusions:

Arid palm groves harbor diverse wetland plant communities whose composition is shaped by regional climate. These systems function as biodiversity hotspots and climatic indicators, highlighting their importance for conservation and research.

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