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Summary: The evolution of angiosperms was accompanied by the segregation and specialisation of their xylem tissues. This study aimed to determine whether the fraction and arrangement of parenchyma tissue influence the hydraulic efficiency–safety trade‐off in the basal angiosperms.We examined xylem anatomical structure and hydraulic functioning of 28 woody species of Magnoliids in a tropical rainforest of Madagascar and reported, for the first time, quantitative measurements that support the relationship between vessel‐to‐xylem parenchyma connectivity and the hydraulic efficiency–safety trade‐off. We also introduced a new measurement – the distance of species from the trade‐off limit – to quantify the co‐optimisation of hydraulic efficiency and safety.Although the basal angiosperms in this study had low hydraulic conductivity and safety, species with higher axial parenchyma fraction (APf) had significantly higher hydraulic conductivity. Hydraulic efficiency–safety optimisation was accompanied by higher APf and vessel‐to‐axial parenchyma connectivity. Conversely, species exhibiting high ray parenchyma fraction and high vessel‐to‐ray connectivity had lower Ks and were further away from the hydraulic trade‐off limit line.Our results provide evidence that axial parenchyma fraction and paratracheal arrangement are associated with both enhanced hydraulic efficiency and safety. [ABSTRACT FROM AUTHOR]

Having a high stature subjects palms to the same constraints as trees, but the lack of cambial growth urges them to adopt a different strategy. We aimed to characterize the spatial organization of xylem tissues and their potential functions in two palm stems: a 30 cm diameter at breast height (DBH) royal palm (Roystonea regia) and a 12 cm DBH Alexandra king palm (Archontophoenix alexandrae). Macroscopic and microscopic anatomical characteristics were assessed at five vertical locations and 5–6 radial locations at each height. Over 9600 vessels across the two stems were drawn manually and measured based on histological sections. Vertically, a hydraulic bottleneck was identified at the first meter, and both stems showed conduit tapering from 4 m to the top. Radially, most water transport and mechanical support were achieved within 2–5 cm below the bark. The larger stem diameter of royal palm may have improved its water transport, storage, and potential for mechanical support compared to king palm. There was a strong trade-off between ground parenchyma and the fiber fraction. However, the correlation between theoretical hydraulic conductivity (K t) and the ground parenchyma fraction, and between K t and the fiber fraction, shifted from positive or non-significant below the bark, to strongly negative close to the center. These changes reflect the functional sectoriality of the palm stems, which may reduce the constraint of trade-offs between water transport, storage, and mechanical support. To conclude, functional sectoriality may have helped both palm species to withstand the hydraulic and mechanical constraints due to high stature. [ABSTRACT FROM AUTHOR]