Stomatal patterning in Bennettitales

Leaf surface development and the plant fossil record: stomatal patterning in Bennettitales

by Rudall P. J., Bateman R. M. (2019)

Paula J. Rudall, Richard M. Bateman,

Royal Botanic Gardens, Kew, Richmond, United Kingdom


In Biological Reviews 94(3) – –


Stomata play a critical ecological role as an interface between the plant and its environment. Although the guard‐cell pair is highly conserved in land plants, the development and patterning of surrounding epidermal cells follow predictable pathways in different taxa that are increasingly well understood following recent advances in the developmental genetics of the plant epidermis in model taxa. Similarly, other aspects of leaf development and evolution are benefiting from a molecular–genetic approach. Applying this understanding to extinct taxa known only from fossils requires use of extensive comparative morphological data to infer ‘fossil fingerprints’ of developmental evolution (a ‘palaeo‐evo‐devo’ perspective).

The seed‐plant order Bennettitales, which flourished through the Mesozoic but became extinct in the Late Cretaceous, displayed a consistent and highly unusual combination of epidermal traits, despite their diverse leaf morphology. Based on morphological evidence (including possession of flower‐like structures), bennettites are widely inferred to be closely related to angiosperms and hence inform our understanding of early angiosperm evolution. Fossil bennettites – even purely vegetative material – can be readily identified by a combination of epidermal features, including distinctive cuticular guard‐cell thickenings, lobed abaxial epidermal cells (‘puzzle cells’), transverse orientation of stomata perpendicular to the leaf axis, and a pair of lateral subsidiary cells adjacent to each guard‐cell pair (termed paracytic stomata). Here, we review these traits and compare them with analogous features in living taxa, aiming to identify homologous – and hence phylogenetically informative – character states and to increase understanding of developmental mechanisms in land plants.

We propose a range of models addressing different aspects of the bennettite epidermis. The lobed abaxial epidermal cells indicate adaxial–abaxial leaf polarity and associated differentiated mesophyll that could have optimised photosynthesis. The typical transverse orientation of the stomata probably resulted from leaf expansion similar to that of a broad‐leaved monocot such as Lapageria, but radically different from that of broad‐leafed eudicots such as Arabidopsis. Finally, the developmental origin of the paired lateral subsidiary cells – whether they are mesogene cells derived from the same cell lineage as the guard‐mother cell, as in some eudicots, or perigene cells derived from an adjacent cell lineage, as in grasses – represents an unusually lineage‐specific and well‐characterised developmental trait. We identify a close similarity between the paracytic stomata of Bennettitales and the ‘living fossil’ Gnetum, strongly indicating that (as in Gnetum) the pair of lateral subsidiary cells of bennettites are both mesogene cells. Together, these features allow us to infer development in this diverse and relatively derived lineage that co‐existed with the earliest recognisable angiosperms, and suggest that the use of these characters in phylogeny reconstruction requires revision.


Stomatal development in Gnetales

Mature stomata on a leaf of Gnetum gnemon. Image: Rudall and Rice 2019.

Epidermal patterning and stomatal development in Gnetales

Salt A. (2019)

In Botany One May 30, 2019 –


Stomatal development in Ephedra differs significantly from that of Gnetum and Welwitschia, more closely resembling that of other extant gymnosperms. Differences in epidermal pre-patterning broadly reflect differences in growth habit between the three genera.

A new study by Rudall and Rice in Annals of Botany looks at Epidermal patterning and stomatal development in Gnetales. The Gnetales are three families of plants that diverged in the Jurassic, before flowering plants, so they are ancient. However, just three genera have survived to the current day. That means they provide a useful group of plants if you want to examine how stomata have developed over millions of years. Dr Paula Rudall made some time to talk to Botany One about her research.

Epidermal patterning and stomatal development in Gnetales (Gymnospermae)

Epidermal patterning and stomatal development in Gnetales

by Rudall P. J., Rice C. L. (2019)

Paula J. Rudall, Callie L. Rice,

Royal Botanic Gardens, Kew, Richmond, TW9, UK


In Annals of Botany, mcz053 – –


Background and Aims

The gymnosperm order Gnetales, which has contentious phylogenetic affinities, includes three extant genera (EphedraGnetumWelwitschia) that are morphologically highly divergent and have contrasting ecological preferences: Gnetum occupies mesic tropical habitats, whereas Ephedraand Welwitschia occur in arid environments. Leaves are highly reduced in Ephedra, petiolate with a broad lamina in Gnetum and persistent and strap-like in Welwitschia. We investigate stomatal development and prepatterning stages in Gnetales, to evaluate the substantial differences among the three genera and compare them with other seed plants.


Photosynthetic organs of representative species were examined using light microscopy, scanning electron microscopy and transmission electron microscopy.

Key Results

Stomata of all three genera possess lateral subsidiary cells (LSCs). LSCs of Ephedra are perigene cells derived from cell files adjacent to the stomatal meristemoids. In contrast, LSCs of Gnetumand Welwitschia are mesogene cells derived from the stomatal meristemoids; each meristemoid undergoes two mitoses to form a ‘developmental triad’, of which the central cell is the guard mother cell and the lateral pair are LSCs. Epidermal prepatterning in Gnetum undergoes a ‘quartet’ phase, in contrast with the linear development of Welwitschia. Quartet prepatterning in Gnetum resembles that of some angiosperms but they differ in later development.


Several factors underpin the profound and heritable differences observed among the three genera of Gnetales. Stomatal development in Ephedra differs significantly from that of Gnetum and Welwitschia, more closely resembling that of other extant gymnosperms. Differences in epidermal prepatterning broadly reflect differences in growth habit between the three genera.

Stomata in Podocarpus

The stomatal complex of Podocarpus observed in cross-section using cryofracture: a preliminary study

by Whiting M., Mill R. R., Jeffree C. E. (2017)

In Edinburgh Journal of Botany 74(3): 345-364 –


Cryofracture of living material and fracture at room temperature of herbarium material were used to obtain cross-sections of the stomatal complexes of four species of Podocarpus (Podocarpaceae) for scanning electron microscopy. Cross-sections of the stomata of one species in Podocarpus subgenus Foliolatus, section Foliolatus (Podocarpus rubens),

one in Podocarpus section Globulus (Podocarpus beecherae), one in Podocarpus subgenus Foliolatus section Longifoliolatus (Podocarpus insularis) and one in subgenus Podocarpus section Australis (Podocarpus nivalis) were studied. The architecture of the stomatal complex, including the wax plug, is described.

It was found that the wax plug sits high in the stomatal antechamber in Podocarpus rubensP. beecherae and Podocarpus decipiens and about halfway up the chamber in P. nivalis. A ridge, which appears to correspond to the crease where the guard cells meet, exists on the underside of the wax plug in Podocarpus beecheraeP. decipiens and P. rubens; its presence in P. nivalis requires confirmation. In addition, ridges within the stomatal antechamber were observed when viewing the cross-sections of Podocarpus decipiens and P. rubens, the internal surface of the cuticle of P. decipiensPodocarpus teysmanniiP. insularis and Podocarpus milanjianus, and the external surface of the cuticle of Podocarpus chinensisPodocarpus macrophyllus and Podocarpus pilgeri. These ridges may consist of wax and be a result of epitaxis.

Stomata in fossil conifers

Zur Unterscheidung fossiler Spaltöffnungen den mitteleuropaischen Coniferen (In German)

by Trautmann W. (1953)

Werner Trautmann, Universität Göttingen (Germany)


In Flora 140: 523-533 – –


Stomata: Pinus, Picea, Taxus, Abies, Larix, Juniperus

Sunken stomata in Pinus (Gymnopsermae)

Photo Google Wikimedia Commons
Cross section: Pinus needle magnification: 400x
A single layered epidermis of lignified cells is covered by a heavy waxy cuticle. Numerous sunken stomata are scattered over the entire epidermal surface. They are bounded by pairs of subsidiary cells, and open internally to a sub-stomatal cavity and externally to a respiratory cavity or vestibule.
The underlying hypodermis consists of several layers of thick-walled sclerenchyma, particularly well-developed at ridges.

10 February 2014, Berkshire Community College Bioscience Image Library

3,264 × 1,840 (5.58 MB)

Stomatal characteristics in Glyptostrobus (Taxodiaceae)

SEM images of stomata. Scale bars = 50 µm. Fig. 11. Stomata of outer surface of a linear leaf collected from Hangzhou. Figs 12, 13. Stomata of inner surface of linear leaves collected from Hangzhou.



Screen Shot 2018-06-04 at 23.47.51
Stomata from linear-subulate leaves collected from Hangzhou. Arrows indicate pits. Scale bars = 30 µm.


Epidermal structures and stomatal parameters of Chinese endemic Glyptostrobus pensilis (Taxodiaceae)

by Ma Q.-W., Li C.-S., Li F.-L., Vickulin S. V. (2004)

Qing-Wen MA, Cheng-Sen LI, Feng-Lan LI, SergeiI V. VICKULIN,


in Botanical Journal of the Linnean Society 146(2): 153–162 –


Glyptostrobus pensilis K. Koch, the only living species, is endemic to southern China. Epidermal structures of Gpensilis have been studied on leaves collected from Guangzhou, southern China, the native locality of the species, and from Hangzhou, eastern China, the cultivated locality.Leaves are linear, linear-subulate and scale-like. Epidermal cells are rectangular and elongate parallel to the mid-vein on areas lacking stomata, and short, with rounded corners, on intrastomatal areas.

Stomatal bands lie parallel to the mid-vein on both surfaces of leaves. Commonly the stomata have five or six subsidiary cells. Stomatal parameters (density and index) of the same surfaces of linear leaves from Guangzhou and Hangzhou show no statistically significant differences (P > 0.05).

Considering the stomatal parameters of the same surfaces of linear-subulate leaves between the two localities, the stomatal index of the abaxial surfaces reveals no significant differences (P > 0.05), while the stomatal index of the adaxial surfaces and the stomatal density of both surfaces exhibit significant differences (P < 0.05). Intra-individual variation in stomatal index is smaller than that in stomatal density based on the coefficient of variability of stomatal parameters of the same areas of leaves.

When studying the correlation between stomatal parameters of G. pensilis and atmospheric CO2 concentrations, the stomatal parameters of linear leaves are mostly significant, and stomatal index is more useful than stomatal density.