Photo credit: Palaeontology
Figure 5 — Stomata of modern plants. (A) Wollemi Pine. (B) Cherry laurel leaf. (C) Baobab. (D) Bay leaf. Credit: L. Seyfullah.
Fossil Focus: Using Plant Fossils to Understand Past Climates and Environments
by Seyfullah L. J. (2012)
Leyla J. Seyfullah, Georg-August-Universität Göttingen, Courant Research Centre Geobiology, Göttingen, Germany.
in Palaeontology Volume 2 | Article 7 | Page 1-8 –
Uses of leaves 3: Leaf cuticle and stomatal density
The cuticle is the waxy surface layer on leaves that protects them from dust, pathogens, mechanical injury and some of the ultraviolet radiation in sunlight. It is also important for regulating temperature and water loss. It is not a solid barrier: to live and grow, plants need efficient gas exchange, which is controlled by the stomata (pores) in the leaves (Fig. 5). The thickness of the cuticle itself is an indicator of how much water stress the plant experiences: the more abundant water is in the environment, the less need the plant has to prevent water escaping, and the thinner the cuticle. So plants with thin cuticles live in areas where water is freely available; these plants include the filmy ferns (Hymenophyllaceae), which are commonly found near waterfalls and are constantly wetted by spray. Plants with thick cuticles, such as cacti and succulents, experience more water stress, and may display other features that reduce water loss, such as sunken stomata and papillae.
There have been numerous experiments on modern plants testing how the density — number per unit area of the leaf — and function of the stomata change with different environmental factors, such as water stress or increased carbon dioxide levels. Overall, this work shows that some living angiosperms (flowering plants) and conifers subjected to high carbon dioxide concentrations have low stomatal densities, whereas plants in very windy conditions have high stomatal densities, but the stomata are very small. Assuming that fossil plants also show this correlation, the relationship between the number of stomata and the number of epidermal cells (the stomatal index) can be a useful palaeoclimate proxy.
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