Secondarily woody lobostemon and echium (boraginaceae) from two mediterranean-climate biodiversity hotspots share similar wood anatomies
Loading...
Date
2024
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier B.V.
Abstract
Lobostemon (Boraginaceae) comprises 28 shrubby species closely related to the herbaceous genus Echiostachys. Both are native to the Greater Cape Floristic Region of South Africa. Together, they form a sister clade to Echium, which is herbaceous except for 23 species that evolved into shrubs and rosette trees on the islands of Macaronesia. Lobostemon and woody Echium make a rare case of parallel evolution of woody habits from herbaceous ancestors (secondary woodiness) in climatically similar but geographically very distant areas. We examined the wood anatomy of 27 Lobostemon species and two of the three species of Echiostachys and compared it with the literature data on woody and herbaceous Echium. Despite differing growth habits, all species share similar wood anatomical traits that may reflect their preference for open, semi-arid habitats. Most conspicuously, there is a common tendency to retain ground tissue cells alive for prolonged periods. In woody species, this results in living fibres and fibre-tracheids. In herbs, it may lead to the total parenchymatization of wood that is devoid of dead cells, except for vessel elements. In Lobostemon, fibre-tracheids with conspicuous pits co-occur with grouped vessels. This may be related to the prolonged retention of protoplasts in ground tissue cells, which hinders water conductance, forcing the development of grouped vessels that can provide a bypass for water in case of embolism.
Description
Keywords
Cape Floristic Region, Carlquist's law, Convergent evolution, Derived woodiness, Drought
Citation
Frankiewicz, K.E., Velani, N., Manuel, R., Lyner, T., Magee, A.R., Boatwright, J.S., Muasya, A.M. and Oskolski, A.A., 2024. Secondarily woody Lobostemon and Echium (Boraginaceae) from two Mediterranean-climate biodiversity hotspots share similar wood anatomies. South African Journal of Botany, 174, pp.116-124.