Cuticle and Stomata in Palaeobotany

 

Plant cuticles and some of their applications in palaeobotany

by Anonymous – (x)

in Uni Muenster

http://www.uni-muenster.de/GeoPalaeontologie/Palaeo/Palbot/cuticles.htm

The cuticle is a non-cellular protective layer covering the outer cell layer (epidermis) of the green, aerial parts of land plants.  Cuticles protect plants against dessication, UV radiation and various kinds of physical, chemical and (micro)biological agents.  Moreover, the cuticle also provides some support.  In fact, the cuticle  which protects the underlying tissues has basically the same function as our own skin.  In several groups of plants cuticles are very resistant and they have a high fossilization potential; only few groups do not generally have highly resistant cuticles (lycopods, Equisetophytes and ferns).

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Very typical features are the so-called stomata which serve for gass exchange, i.e. the uptake of carbondioxide and release of oxygen.  Stomata consist of an opening or stomatal pore, and two kidney-shaped guard cells. The guard cells  are used for opening and closing the stomatal pore, in order to regulate the evapotranspiration and gass exchange.   Early land plants and several angiosperms have such simple stomata.  In many gymnosperms stomata and surrounded by cells that are differently shaped from the normal epidermal cells.  Usually stomata are surrounded by one ring of neighbouring cells, occasionally a second ring of encircling cells occurs.  The stoma together with the neighbouring (and encircling) cells is then called a stomatal complex or stomatal apparatus.  Stomata are often more common on the lower leaf surfaces; not rarely they are completely restricted to lower leaf surfaces; being in the shade reduces the risk of excessive water loss.  For the same reason stomata may also be sunken and stomatal pores may be covered by overhanging papillae (see below).  Not only the shape of the stomata is typical, but also their distribution (e.g., concentrated, randomly, in rows) and the orientation are useful diagnostic characters.

 

Leaf cuticle of Symplocos hallensis(Eocene) with three stomata 
each consisting of two guard cells
Axial cuticle of the Early Devonian land plant Aglaophyton major with stoma consisting of two guard cells Leaf cuticle of the Early Permian pteridosperm Autunia conferta
with stomatal complexes

 

Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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