Premise of research: The morphology of leaves is shaped by both historical and current selection acting on constrained developmental systems. For this reason, the phylogenetic signal of these characters is usually overlooked. Methodology: We investigate morphology of the leaflets of all genera of the Zamiaceae using multiple microscopical techniques to test whether leaf characters present a phylogenetic signal and whether they are useful to define clades at a suprageneric level. Pivotal results: Our investigation shows that most genera are quite uniform in their leaflet anatomy, with the largest genera (Zamia, Encephalartos) presenting the highest degree of variation. Using both Bayesian and parsimony methods on two different molecular scaffolds, we are able to show that leaflet anatomy has a strong phylogenetic signal in the Zamiaceae and that many clades retrieved by molecular analyses present potential synapomorphies in their leaflet anatomy. Particularly, the placement of Stangeria in a clade with Zamia and Microcycas is supported by the presence of both an adaxial and an abaxial girder sclerenchyma and the absence of sclerified hypodermis. The placement of Stangeria as sister to Bowenia, on the other hand, is not supported by our analysis. Instead, our results put into question the homology of the similar guard cell morphology in the two genera. Conclusions: We show that leaflet anatomy has a substantial amount of phylogenetic signal in the Zamiaceae, supporting relationships that are not supported by general morphology. Therefore, anatomical investigation represents a promising avenue for plant systematists.

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Numerous specimens from several species of the Paleozoic marattialean fern genus Psaronius Cotta were collected from Upper and Middle Pennsylvanian deposits in Ohio, Illinois, and Kansas. I suggest that, as the Psaronius plant grew, basal portions of the stem and bound root zone decayed. This conclusion is based on specimens in which the stem and bound root zone are completely or partially lacking, the paucity of very basal trunk segments known for the genus, and evidence from living analogs. Secondary parenchyma in P. chase Morgan and P. blicklei Morgan is described as localized areas of radially aligned cells in stems and outer cortex. Linear regressions of number of orthostichies, stelar cycles, and inner meristeles versus stem diameter indicate that vascular ontogeny may have occurred at different rates among some species of Psaronius. Analysis of Psaronius stem anatomy and morphology suggests that, in general, stems had an open, unidirectional growth mode with a continuously expanding apex and vascular tissue of both cauline and foliar origin.

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Populus nigra L. (black poplar) possesses amphistomatic leaves, with large\ud (giant) and normal sized stomata. The role of giant stomata in leaf development,\ud and the consequences on stomatal density in adult leaves remains elusive.\ud This paper describes the characteristics of ordinary and giant stomata in\ud leaves of two black poplar genotypes (58-861 with large leaves from northern\ud Italy, and Poli with small leaves from southern Italy). Stomatal traits in both\ud genotypes were studied using light microscopy on mature leaf adaxial and\ud abaxial epidermal impressions. Moreover, scanning electron microscopy was\ud applied to study giant and normal stomata in early, young, and mature leaves.\ud Leaf abaxial surfaces in the two genotypes revealed variable sizes and patterns\ud of stomata related to differences in intrinsic water use efficiency (Wi). These\ud observations provided evidence of different stomatal types in mature black\ud poplar leaves, and new information regarding the presence and potential role\ud of giant stomata in black poplar leaves