Abstract: Alfalfa (Medicago sativa L.) is a globally important perennial legume forage whose productivity and persistence are strongly constrained by water availability. Xylem vessels serve as the primary pathway for long-distance water transport, and their anatomical characteristics underpin the classical trade-off between hydraulic efficiency and embolism resistance. Previous studies have mainly focused on single traits such as vessel diameter and density, whereas the spatial distribution of vessels at the tissue scale and its functional significance have received less attention. In recent years, spatial point pattern analysis, particularly the Strauss–Hardcore point process model, has been increasingly applied to quantify the two-dimensional spatiial arrangement of xylem vessels, providing new insights into vessel spatial heterogeneity. This model characterizes vessel spatial configurations under physical exclusion and local interaction constraints using key parameters, including hard-core distance (h), interaction distance (R), and pairwise interaction strength (γ). Accumulating evidence suggests that xylem vessel spatial patterns in Alfalfa (Medicago sativa L.) vary markedly among genotypes and environmental conditions and are closely associated with hydraulic safety, water-use efficiency, and drought tolerance. This review synthesizes recent advances in the application of the Strauss–Hardcore model to studies of xylem vessel spatial distribution in alfalfa, discusses the potential bet ween vessel spatial configurations and hydraulic trade-offs, and summarizes vessel network plasticity in response to drought, salinity, and nutrient availability. Furthermore, we highlight recent progress in the molecular regulation of vessel development and outline future directions integrating three-dimensional imaging and multi-omics approaches to better understand the ecological significance of xylem spatial organization.

Key words: Alfalfa (Medicago sativa L.), xylem vessel, spatial point pattern, Strauss–Hardcore model, hydraulic trade-off, environmental stress