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Summary Many plant leaves have two layers of photosynthetic tissue: the palisade and spongy mesophyll. Whereas palisade mesophyll consists of tightly packed columnar cells, the structure of spongy mesophyll is not well characterized and often treated as a random assemblage of irregularly shaped cells.Using micro‐computed tomography imaging, topological analysis, and a comparative physiological framework, we examined the structure of the spongy mesophyll in 40 species from 30 genera with laminar leaves and reticulate venation.A spectrum of spongy mesophyll diversity encompassed two dominant phenotypes: first, an ordered, honeycomblike tissue structure that emerged from the spatial coordination of multilobed cells, conforming to the physical principles of Euler’s law; and second, a less‐ordered, isotropic network of cells. Phenotypic variation was associated with transitions in cell size, cell packing density, mesophyll surface‐area‐to‐volume ratio, vein density, and maximum photosynthetic rate.These results show that simple principles may govern the organization and scaling of the spongy mesophyll in many plants and demonstrate the presence of structural patterns associated with leaf function. This improved understanding of mesophyll anatomy provides new opportunities for spatially explicit analyses of leaf development, physiology, and biomechanics.
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This content will become publicly available on December 15, 2025
Into the spongy-verse: structural differences between leaf and flower mesophyll
As the site of almost all terrestrial carbon fixation, the mesophyll tissue is critical to leaf function. However, mesophyll tissue is not restricted only to leaves but also occurs in the laminar, heterotrophic organs of the floral perianth, providing a powerful test of how metabolic differences are linked to differences in tissue structure. Here, we compared mesophyll tissues of leaves and flower perianths of six species using high-resolution X-ray computed microtomography (microCT) imaging. Consistent with previous studies, stomata were nearly absent from flowers, and flowers had a significantly lower vein density compared to leaves. However, mesophyll porosity was significantly higher in flowers than in leaves, and higher mesophyll porosity was associated with more aspherical mesophyll cells. Despite these differences in cell and tissue structure between leaf and flower mesophyll, modeled intercellular airspace conductance did not differ significantly between organs, regardless of differences in stomatal density between organs. These results suggest that in addition to differences between leaves and flowers in vein and stomatal densities, the mesophyll cells and tissues inside these organs also exhibit marked differences that may allow for flowers to be relatively cheaper in terms of biomass investment per unit of flower surface area.
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- Award ID(s):
- 2029756
- PAR ID:
- 10550148
- Publisher / Repository:
- OUP
- Date Published:
- Journal Name:
- Integrative and comparative biology
- ISSN:
- 1557-7023
- Subject(s) / Keyword(s):
- flower, flower anatomy, functional plant anatomy, intercellular airspace, leaf, leaf anatomy, microCT, spongy mesophyll, structure-function relations
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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