The widespread recognition of the scientific importance of leaf architecture, the description and interpretation of leaf shape and venation, is a cornerstone contribution of Leo Hickey's career. One leaf architectural trait that Hickey developed is leaf rank, which describes the level of organization of leaf venation in a single, discrete, ordinal variable. He used this scoring system to provide a rapid summary of overall venation complexity and organization in modern and fossil leaves. Leaves with the most reduced and disorganized venation are scored as low rank, whereas leaves with complex and well-organized venation are given high values. Leaf rank data facilitated comparisons of early angiosperms in fossil floras and were invoked in hypotheses regarding angiosperm evolution and ecology. This study presents a large data set of leaf ranks that Leo Hickey scored while he was a researcher at the Smithsonian Institution from 1969 to 1982. The data set represents at least 2,435 observations of US National Herbarium specimens. These formative observations of leaf venation have never been published. Here, we examine Hickey’s data in light of current angiosperm phylogeny as a way to reinvestigate several of his hypotheses regarding leaf rank and angiosperm evolution: (1) leaf ranks tend to be consistent within a family; (2) leaf rank was low in early angiosperms, and high-rank venation occurred later; and (3) leaf rank is correlated with environmental conditions, often with reduced leaf rank values appearing in xeric taxa compared with close relatives under mesic conditions. These hypotheses have not been tested in the light of DNA-based, angiosperm-wide phylogeny, which was not available at the time when leaf rank was developed. We show that even with a DNA-based phylogeny, family-level comparisons show significant differences in average leaf rank; inferred leaf rank states along the early backbone of the angiosperm phylogeny are low, with high-rank taxa occurring across derived lineages; and there is a definite trend toward reduced leaf rank in xeric taxa, all consistent with Hickey’s hypotheses. This taxonomically rich set of observations can serve as a foundation for further investigations of the evolution of leaf vein organization.

Understanding the phylogenetic diversification of the water lilies (Nymphaeales sensu lato) in deep time is currently on the rise through studies based on both molecular analyses and the fossil record. An enhanced data set of leaf architectural and vegetative characters, for example, was found to be in broad agreement with phylogenies based only on molecular characters. Yet questions remain open regarding the relationships among the genera and subgenera of Nymphaea, the minimum time of divergence of familial and subfamilial clades and the phylogenetic radiation of the nymphaeoids during the Cenozoic that led to the living genera. Here we build on the aforementioned enhanced data set by adding a suite of nine, new or previously studied, Early to Late Cretaceous and Cenozoic fossil leaves to elucidate the phylogenetic positions of the fossil taxa, to test hypotheses based on molecular studies and to resolve phylogenetic relationships within Nymphaeales. In our phylogenetic analysis, five fossil leaf species show strong relationships with Nymphaeaceae and weaker subfamilial relationships to Nymphaea subgenus Lotos and to the Victoria—Euryale clade. Three fossil leaf species have strong relationships to Cabombaceae and are stem taxa. Taken as a whole, these new phylogenetic analyses yield strong evidence for the monophyly of the living families and some subfamilial clades. They also provide support for a divergence of Cabombaceae and Nymphaeceae by the Early Cretaceous. Finally, they suggest that some subfamilial clades of Nymphaeaceae may have originated by the Albian—Cenomanian, at the time of rapid diversification of the early angiosperms.

In their 1977 study on Potomac Group angiosperms, Hickey and Doyle made only broad comparisons with living taxa. Newer data, especially discoveries of fossil flowers in the Potomac and coeval deposits and increasingly robust molecular phylogenies of living angiosperms, allow more precise phylogenetic placement of fossils. Hickey and Doyle compared most early Potomac leaves (Aptian—early Albian) with “magnoliids,” a paraphyletic group as then defined, but several clades can now be recognized. Leaves and dispersed cuticles share epidermal features with woody members of the basal ANITA grade, and in some cases crown group Austrobaileyales, whose presence is confirmed by flowers called Anacostia. Aptian—Albian flowers (Monetianthus, Carpestella) and whole plants (Pluricarpellatia) are nested in crown group Nymphaeales; Potomac reniform leaves could belong to this clade. Several Potomac leaves have chloranthoid teeth, venation, and opposite phyllotaxis consistent with Chloranthaceae, while Aptian to Cenomanian flowers reveal the presence of both crown group Chloranthaceae (Asteropollis plant, near Hedyosmum) and stem relatives of this family and/or Ceratophyllum (Canrightia, Zlatkocarpus, Pennipollis plant, possibly Appomattoxia). Phylogenetic analyses confirm interpretations of Aptian Liliacidites pollen and Acaciaephyllum as monocots. Ternately lobed leaves such as Vitiphyllum may represent basal eudicots, in or below Ranunculales. In the late Potomac (middle to late Albian), the rise of tricolpate pollen and local dominance of angiosperm leaves mark the influx of near-basal eudicot clades. Associated floral receptacles confirm that Nelumbites leaves were related to Nelumbo (Proteales), while heads of unisexual flowers indicate that both palmately lobed “platanoid” and pinnatifid Sapindopsis leaves (previously compared with rosids) were stem relatives of Platanus (also Proteales). Flowers called Spanomera are related to Buxaceae. Several Albian and early Cenomanian flowers belong to Magnoliidae in the new monophyletic sense, including Archaeanthus in Magnoliales and Virginianthus and Mauldinia in Laurales; Laurales are common in the late Albian leaf record.

Plant fossil collections from Lower Cretaceous floodplain deposits sometimes provide snapshots of local communities that included early herbaceous angiosperms. Here I describe the plant megafossils in a collection made from the lower part of the Potomac Group near Fairlington, Virginia, USA. The collection includes 123 identifiable plant fossils on 42 hand specimens, comprising nine plant morphotypes: three ferns, five gymnosperms and one angiosperm. All but one of the described morphotypes also occur in other collections from the lower Potomac Group. There is one moderately abundant angiosperm species in this collection that has been found at other Potomac Group sites but was incorrectly identified as a fern. Well-preserved specimens of this morphotype clearly show axillary branching, complex leaves and glandular teeth at the apices of lobes on the leaves; together, these characteristics suggest it was an herbaceous eudicot angiosperm. The one new morphotype in this collection is an enigmatic plant of intermediate abundance and unknown affinity. On the basis of the simple, pinnate stenophyllous leaves with two vein orders, reticulate secondary veins and the attachment of one leaf to a carbonized axis roughly 1 cm across with long internodes, I hypothesize that it was a shrubby riparian gymnosperm. This work represents the first step toward a complete morphotype catalog for the flora of the lower Potomac Group.

Abundant plant fossils were recovered from Albian fluvial and back-swamp sediments of the Jarash Formation (Kurnub Group) of Jordan. The flora consists of angiosperms, ferns and gymnosperms. Water lily Scutifolium jordanicum, marsilealean fern Marsileaceaephyllum mahisensis and tree fern Weichselia reticulata are from a thin crevasse splay layer of a small fluvial system. Four species of other ferns, Phlebopteris hickeyi sp. nov., Piazopteris branneri, Aspidistes beckeri and Cladophlebis sp., and two gymnosperms, Zamites hoheneggeri and Brachyphyllum mamillare, are from a back-swamp dark gray carbonaceous lens. Phlebopteris hickeyi represents a new fern species that has five preserved pinnae with unique characteristics, including small sori and sporangia. The relatively small pinnules with massive midveins and grooves along either side of midveins represent a unique combination of characters. The water lily S. jordanicum and marsilealean fern M. mahisensis may have grown in ponds, lakes or slow-moving streams along the margin of the back-swamps. However, the tree fern W. reticulata is thought to have grown in tropical coastal areas. The co-occurrence of W. reticulata with S. jordanicum and M. mahisensis indicates that the habitat of water lily and marsilealean fern was not far from the coast. Additionally, M. mahisensis suggests the presence of dry seasons because extant Marsileaceae need a dry terrestrial phase for reproduction, which is consistent with climate implied from the xerophilic characters of W. reticulata. The matoniaceous fern Phlebopteris hickeyi, Piazopteris branneri, A. beckeri and bennettitalean Z. hoheneggeri were probably growing in the back-swamps. However, the conifer B. mamillare probably grew in coastal areas close to the back-swamps.

Six fossil leaf species are described from impression fossils collected from the Paleocene Fort Union Formation in the Williston Basin in southwestern North Dakota, USA. They are Meliosma vandaelium sp. nov., Meliosma thriviensis sp. nov., Ternstromites paucimissouriensis sp. nov., Macginitiea nascens sp. nov., Dicotylophyllum horsecreekium sp. nov. and Dicotylophyllum hansonium sp. nov. These species represent some of the elements of the Fort Union Formation that are biostratigraphically important megafloral zone taxa or are species that demonstrate an evolutionary relationship to floras from the Eocene Golden Valley Formation. Some of the species described here suggest that new species endemic to the Williston Basin evolved through the Paleocene and into the Eocene. If the pattern of the origination of endemic daughter species seen in the Williston Basin is consistent across the Western Interior basins of North America, it might have driven up gamma diversity through the Paleogene. This provides a possible explanation for the relatively steep vegetation diversity gradients seen in mid- and high-latitude pollen floras in North America during the late Paleocene and early Eocene.

The term parichnos, coined in 1891, has been used since then with more or less precision to describe a morphological or anatomical feature in several taxa of fossilized lycopsids. The parichnos is a tissue system found surrounding or accompanying the (vascular) leaf traces on their paths from the stele to the leaves. By analogy, the term has also been applied to features of some extant lycopsids. Associated with the minor, semantic issue of precisely defining the term, there is the problem of fully understanding the underlying feature that it describes, and a substantive debate about the function of that anatomical or morphological feature. In this article, I review the history of the term and of the associated problem of interpreting the nature and function of the parichnos system. This examination illustrates the constraints that morphological terminology can place on theories of plant function and in turn how accepted ideas about plant function affect the interpretation of observed morphology.

Fossil carettochelyine turtles are well known from the Paleogene of Europe (Allaeochelys), North America and Asia (Anosteira); however, the previously known Neogene fossil record is highly fragmentary and was therefore unsuitable for taxonomic analysis. In this work, we present a new carettochelyine taxon, Allaeochelys libyca, from the Middle Miocene (Langhian) of Gebel Zelten (Libya) based on an incomplete skull and disarticulated postcranial elements. The new taxon is diagnosed relative to the extant Carettochelys insculpta based on the placement of the foramen posterius canalis carotici interni close to the fenestra postotica, the horizontal orientation of the tubercula basioccipitalis, the substantial contribution of the opisthotic to the base of the tubercula basioccipitalis, the presence of a triangular pterygoid fossa, the arrangement of the mandibular condyles along a plane and the presence of an extremely well-developed fossa at the base of the processus mandibularis. A phylogenetic analysis of pancarettochelyids confirms the monophyly of Carettochelyidae and Carettochelyinae but resulted in a paraphyletic taxon, Allaeochelys. For the sake of nomenclatural stability, we provisionally retain the genus Allaeochelys as paraphyletic relative to the extant Carettochelys insculpta.

The fossil record of turtle reproduction (e.g., eggs, embryos, nests and copulating pairs) is relatively poor compared with that of dinosaurs. This record extends from the Middle Jurassic to the Pleistocene, and specimens are known from every continent except Antarctica. Fossil turtle eggs are recognized as body fossils, and confident taxonomic identification at the genus or species level is dependent on embryos preserved within fossil eggs or by eggs found within a gravid female. Cladistic analysis of egg and eggshell characters demonstrates a high degree of homoplasy, and only a few characters provide a strong phylogenetic signal. Taphonomic studies of fossil turtle eggs are rare but can elucidate size and number of eggs produced by extinct taxa. Pathological fossil turtle eggs are known from a few localities and provide information about physiological or environmental stresses experienced by the gravid female. Fossil turtle eggs are relatively abundant in Asia, Europe and North America but are poorly represented in Gondwana. An ootaxonomic review of fossil turtle eggs shows that of 15 named ootaxa, 8 are nomina valida, 5 are nomen nudum and 2 are junior synonyms of other ootaxa.

Percina brucethompsoni, the Ouachita Darter, is described as a new species endemic to the Ouachita River system in the Ouachita Highlands of Arkansas. Bruce Thompson first noted the distinctiveness of the new species from the nominal P. nasuta distributed in the White River and Arkansas River basins in his 1977 doctoral dissertation. The new species is delimited through morphological comparisons with P. nasuta and a phylogenetic analysis of the Percina subclade Swainia using two mitochondrial genes. More than 385 specimens were examined for the morphological comparisons, and 54 specimens were sampled for mitochondrial DNA sequencing. Percina brucethompsoni is distinguished from P. nasuta by a shorter snout, a broader and deeper head, six versus seven branchiostegal rays and specific patterns of lateral pigmentation on the side of the body. Phylogenetic analysis of DNA sequences sampled from two regions of the mitochondrial genome indicate that P. brucethompsoni is the sister species of P. nasuta populations in the White River drainage. Neither P. nasuta nor P. phoxocephala are monophyletic in the mitochondrial DNA gene tree. Specimens of P. phoxocephala from the Red River drainage are resolved as the sister lineage of a clade containing all other sampled populations of P. phoxocephala, P. brucethompsoni and P. nasuta. Percina nasuta and P. phoxocephala sampled from the Arkansas River drainage form a clade that is the sister lineage of a clade containing P. brucethompsoni and P. nasuta from the White River drainage.