Sunken, covered, and encrypted stomata in relation to dry habitats

Stomatal protection in Proteaceae. Note that these structures all supplement the protection provided by the outer cuticular ledges present in most vascular plants. Figs. 1–3, 7–8 light micrographs; Figs. 4–6, scanning electron micrographs. 1.Transverse section of a Banksia ericifolia leaf showing the closely revolute margins. Note the dense hairs in the grooves created by the leaf margin.2.Transverse section of a Grevillea striata leaf showing two hair‐lined grooves that contain the stomata. Note the dense hairs in the left hand groove.3.Transverse section of a Hakea lissosperma leaf showing an individual crypt.4.External surface of a H. lissosperma leaf showing the aperture of an individual crypt.5.External, abaxial surface of a Banksia quercifolia leaf showing the hair‐filled apertures of two pits.6.Inner surface of the abaxial cuticle of a Banksia quercifolia leaf (prepared by maceration in chromium trioxide) showing the balloon‐like crypt. Two stomata are indicated with arrows. 7.Transverse section of a Telopea truncata leaf showing a papillose pit. 8.Transverse section of a Leucadendron pubescens leaf showing a papillose pit. Scale bars: Fig. 1 = 500 μm; Fig. 2, 5 = 200 μm; Figs. 3, 4, 6–8 = 50 μm.

 

The evolutionary relations of sunken, covered, and encrypted stomata to dry habitats in Proteaceae

by Jordan G. J., Weston P. H., Carpenter R. J., Dillon R. A., Brodribb T. J. (2008)

School of Plant Science, University of Tasmania, Private Bag 55, Hobart 7001, Australia

Gregory J. Jordan, Peter H. Weston, Raymond J. Carpenter, Rebecca A. Dillon, Timothy J. Brodribb

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in Am. J. Bot. 95(5): 521-530 – https://doi.org/10.3732/ajb.2007333 –

https://onlinelibrary.wiley.com/doi/full/10.3732/ajb.2007333

Abstract

Sunken, covered, and encrypted stomata have been anecdotally linked with dry climates and reduced transpiration and therefore have been used to infer dry palaeoclimates from fossils.

This study assesses the evolutionary and ecological associations of such stomatal protection in a model system—the diverse southern hemisphere family Proteaceae. Analyses were based on the morphology of over 1400 Australian, South African, New Caledonian, New Zealand, and South American species, anatomy of over 300 of these species, and bioclimatic data from all 1109 Australian species.

Ancestral state reconstruction revealed that five or six evolutionary transitions explain over 98% of the dry climate species in the family, with a few other, minor invasions of dry climates.

Deep encryption, i.e., stomata in deep pits, in grooves, enclosed by tightly revolute margins or strongly overarched by cuticle, evolved at least 11 times in very dry environments.

Other forms of stomatal protection (sunken but not closely encrypted stomata, papillae, and layers of hairs covering the stomata) also evolved repeatedly, but had no systematic association with dry climates.

These data are evidence for a strong distinction in function, with deep encryption being an adaptation to aridity, whereas broad pits and covered stomata have more complex relations to climate.