Palatability of geophyte underground storage organs partially explains their depth in the Cape Floristic Region, geophyte capital of the world
5 affiliations
- 1School of Natural Resource Management, Science Faculty Nelson Mandela University George 6530 South Africa
- 2Palaeo‐Research Institute University of Johannesburg Auckland Park 2006 South Africa
- 3Royal Botanic Gardens, Kew Richmond Surrey UK
- 4Department of Conservation Ecology and Entomology Stellenbosch University Stellenbosch 7599 South Africa
- 5African Centre for Coastal Palaeoscience, Department of Botany Nelson Mandela University Gqeberha 6031 South Africa
Abstract
Premise: The soil depth of underground storage organs (USOs) of geophytes involves cost–benefit trade‐offs and may relate to USO age, size, and disturbances such as fire and herbivory. Yet determinants of USO depth are poorly studied. We posit that belowground mammalian predation of USOs is a selective force for the positive relationship between USO size and depth.
Methods: We tested the mammalian predation hypothesis using USO depth, mass, type (bulb, corm, tuber, rhizome) and palatability to human foragers for 1828 geophyte individuals (153 species, 54 genera, 22 families) from the lowlands of the Cape Floristic Region (South Africa) which harbors the world's highest concentration of geophytes.
Results: USOs were found at depths of 0–34 cm, but depth had no consistent relationship with mass. The depth–mass relationship was instead related to USO type: Compared with smaller counterparts, larger bulbs were at shallower depths, and larger corms were deeper. USO palatability affected the depth–mass relationship; palatability was generally associated with deeper burial across USO types: Palatable corms, tubers, and rhizomes mostly had positive depth–mass relationships, and unpalatable types had no relationship. Palatable bulbs had negative relationships that were less significant than for unpalatable bulbs. The phylogenetic signal in the study species was only moderate.
Conclusions: USO type and palatability explained some variation in their depth–mass relationship in accordance with the mammalian predation hypothesis. USO age and shape, soil type, and predation strategy and intensity should be explored as potential additional correlates of USO depth and size.
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BibTeX
@article{kraaij2026palatability,
title = {{Palatability of geophyte underground storage organs partially explains their depth in the Cape Floristic Region, geophyte capital of the world}},
author = {Tineke Kraaij and Elzanne Singels and Félix Forest and Karen J. Esler and Richard M. Cowling},
journal = {American Journal of Botany},
year = {2026},
month = oct,
doi = {10.1002/ajb2.70271},
url = {https://doi.org/10.1002/ajb2.70271},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Palatability of geophyte underground storage organs partially explains their depth in the Cape Floristic Region, geophyte capital of the world
AU - Tineke Kraaij
AU - Elzanne Singels
AU - Félix Forest
AU - Karen J. Esler
AU - Richard M. Cowling
PY - 2026
DA - 2026/10/07
JO - American Journal of Botany
DO - 10.1002/ajb2.70271
UR - https://doi.org/10.1002/ajb2.70271
AB - Premise: The soil depth of underground storage organs (USOs) of geophytes involves cost–benefit trade‐offs and may relate to USO age, size, and disturbances such as fire and herbivory. Yet determinants of USO depth are poorly studied. We posit that belowground mammalian predation of USOs is a selective force for the positive relationship between USO size and depth. Methods: We tested the mammalian predation hypothesis using USO depth, mass, type (bulb, corm, tuber, rhizome) and palatability to human foragers for 1828 geophyte individuals (153 species, 54 genera, 22 families) from the lowlands of the Cape Floristic Region (South Africa) which harbors the world's highest concentration of geophytes. Results: USOs were found at depths of 0–34 cm, but depth had no consistent relationship with mass. The depth–mass relationship was instead related to USO type: Compared with smaller counterparts, larger bulbs were at shallower depths, and larger corms were deeper. USO palatability affected the depth–mass relationship; palatability was generally associated with deeper burial across USO types: Palatable corms, tubers, and rhizomes mostly had positive depth–mass relationships, and unpalatable types had no relationship. Palatable bulbs had negative relationships that were less significant than for unpalatable bulbs. The phylogenetic signal in the study species was only moderate. Conclusions: USO type and palatability explained some variation in their depth–mass relationship in accordance with the mammalian predation hypothesis. USO age and shape, soil type, and predation strategy and intensity should be explored as potential additional correlates of USO depth and size.
SN - 0002-9122
SN - 1537-2197
ER -