Kathleen B. Pigg

Evolution of Isoetalean Lycopsids

The recognition of numerous similarities between Isoetes L. and extinct arborescent lycopsids historically led to one of the best Known phylogenetic lineages in vascular plant evolution. The lycopsid reduction series proposed the derivation of the extant guillwort Isoetes from the Carboniferous lepidodendrids through a progressive reduction in both stems and stigmarian rooting systems. New information gained in the past decade demonstrates that the history of this group is more complex than the linear reduction sequence suggests (...)

Chaloneria Gen. Nov.; Heterosporous Lycophytes from the Pennsylvanian of North America

Several hundred permineralized fragments of a single type of plant occur in upper Pennsylvanian coal balls from the Appalachian Basin, and these provide evidence for the description and complete reconstruction of a new heterosporous lycophyte. Chaloneria cormosa gen. et sp. nov. is unbranched, ca. 2 m tall, and has a rounded rooting base. Secondary xylem is abundant at the base, diminishes distally, and is absent from the apical region. The stem has ligulate microphylls that are vegetative at proximal levels and grade upward into a fertile apex. Leaf cushions are not produced. In the fertile zone there are alternating regions of megasporophylls and microsporophylls. A second species, Chaloneria periodica sp. nov., has alternating vegetative and fertile zones and is based on Middle Pennsylvanian specimens that were previously referred to Polysporia mirabilis. Spores of both species are assignable to Valvisisporites and Endosporites. Plants with these sporomorphs comprise several genera rather than the single species P. mirabilis.

Isoetalean Lycopsid Evolution: from the Devonian to the Present

Abstract The evolution of the isoetalean lycopsids spans much of the history of vascular plants, from Late, (or possibly Middle), Devonian to the current day genus Isoetes. The best known fossil members of this group are the arborescent lepidodendrids that dominated the Late Carboniferous coal swamps. Simpler unbranched isoetaleans with elongate stems also predated, coexisted with, and postdated the coal swamp trees, extending well into the Mesozoic. Whereas certain synapomorphies such as stigmarian rootlets, bipolar growth and secondary tissues unite the clade, other features characterize smaller subgroups of differing age, growth form and possibly, evolutionary lineage. Although some of these features are well known for plants of given time periods, particularly the Carboniferous, trends in character evolution have never been adequately documented for the group as a whole. A better understanding of such trends throughout the isoetalean fossil record could be valuable in distinguishing evolutionary lineages from convergence. It is interesting that several morphological characters of modern Isoetes are present as early as the Triassic: monolete microspores, sunken sporangia and elaborate ligules with glossopodia occur within elongate-stemmed Triassic forms. The dominant plant habit of modern Isoetes, a reduced cormose form that lacks appreciable stem elongation, originated at least by the Jurassic and typifies late Mesozoic and Cenozoic isoetaleans.

A brief review of the fossil history of the family Rosaceae with a focus on the Eocene Okanogan Highlands of eastern Washington State, USA, and British Columbia, Canada

Many of the oldest definitive members of the Rosaceae are present in the Eocene upland floras of the Okanogan Highlands of northeastern Washington State and British Columbia, Canada. Over a dozen rosaceous taxa representing extant and extinct genera of all four traditionally recognized subfamilies are known from flowers, fruits, wood, pollen, and especially leaves. The complexity seen in Eocene Rosaceae suggests that hybridization and polyploidy may have played a pivotal role in the early evolution of the family. Increased species diversity and the first appearance of additional modern taxa occur during the Late Paleogene in North America and Europe. The Rosaceae become increasingly important components of fossil floras during the Neogene, with taxa adapted to many habitats.

The Princeton chert: Evidence for in situ aquatic plants

Abstract The Middle Eocene Princeton chert from southern British Columbia represents one of the richest known assemblages of permineralized Tertiary plants. Affinities with modern aquatic angiosperms, anatomical modifications for the aquatic habit and associated fresh water faunal elements support the interpretation of some components of the Princeton chert as in situ aquatic plants. Among these are fossil plants with affinities to the extent Nymphaeaceae ( Allenbya ), Araceae ( Keratosperma ), Alismataceae ( Heleophyton ), Cyperaceae/Juncaceae ( Ethela ) and Lythraceae ( Decodon ). Anatomical modifications include aerenchyma in vegetative tissues ( Eorhiza, Dennstaedtiopsis, Heleophyton and Uhlia ), the thin-walled tracheary elements without prominent secondary wall thickenings and the presence of protoxylem lacunae surrounded by a ring of cells with thickened inner walls ( Heleophyton ). Seeds that share morphological features with extant aquatics are characterized by a palisade layer, operculum, external mucilage, small amounts of endosperm and abundant perisperm. Associated faunal elements include turtle bones in the peat matrix and freshwater fish at the top of the section. In situ preservation of these aquatic forms is supported by the presence of rooted axes, the large number of plant organs of the same type and preservation of complete flowers, delicate tissues and organic connections allowing for whole plant reconstruction.

Anatomically Preserved Glossopteris Stems with Attached Leaves from the Central Transantarctic Mountains, Antarctica

Stems and buds of Glossopteris skaarensis Pigg and buds of G. schopfii Pigg from the Permian Skaar Ridge locality in the central Transantarctic Mountains, Antarctica demonstrate the first anatomically preserved glossopterids known with stem/leaf attachment. Stems of G. skaarensis are 1-12 mm in diameter ( = 3.1 mm) with a broad pith, poorly defined primary xylem, and a zone of secondary xylem up to 6 mm thick. Pycnoxylic wood conforming to Araucarioxylon Kraus is composed of tracheids with uni- to biseriate oval to hexagonal bordered pits on radial walls, uniseriate rays one to a few cells high, and cupressoid to taxodioid cross-field pitting. Stems have a narrow zone of secondary phloem, aerenchymatous cortex with scattered sclereids, and sometimes a narrow periderm. Two wedge-shaped leaf traces each bifurcate to form four strands in the base of each petiole. Small axillary branches are vascularized by double branch traces that fuse at the margin of the main axis. Buds of G. skaarensis have leaves with narrow lateral laminae and a thickened midrib containing a wide lacuna, delicate vascular strands, and a prominent hypodermis. In contrast, buds of G. schopfii have uniformly thick leaves with prominent, circular vascular bundle sheaths. These anatomical details are used to reconstruct individual types of glossopterid plants, providing new information toward understanding the ecology and evolution of this important group of Permian seed plants.

Platanaceous plants from the Paleocene of Alberta, Canada

A new platanaceous plant is described from the Joffre Bridge locality from the Paleocene of western Canada. The plant is based upon a suite of distinctive platanaceous remains. These include: foliage leaves that resemble Platanus nobilis Newberry, pistillate inflorescences and infructescences assigned to a new species of Macginicarpa Manchester, M. manchesteri Pigg et Stockey, sp. nov., staminate inflorescences assigned to a new species of Platananthus Manchester emend. Friis et al., P. speirsae Pigg et Stockey, sp. nov., isolated groups of stamen clusters containing platanaceous pollen, and young seedlings in several stages of development. Based on their exclusive co-occurrence at a single locality these disarticulated organs are thought to represent the same platanaceous plant. The reconstruction of the Joffre plane tree is the second “whole plant” reconstruction from the Joffre Bridge locality. Along with the cercidiphyllaceous Joffrea speirsii Crane and Stockey, the Joffre plane tree can be included among the best known Paleocene angiosperms.

Corylus, Carpinus, and Palaeocarpinus (Betulaceae) from the Middle Eocene Klondike Mountain and Allenby Formations of Northwestern North America

Coryloid reproductive remains (Betulaceae, subfamily Coryloideae) are documented from the middle Eocene Republic flora of northeastern Washington State and the Princeton flora of southern British Columbia. The oldest confirmed examples of two modern genera, Corylus johnsonii Pigg, Manchester & Wehr sp. nov., and Carpinus perryae Pigg, Manchester & Wehr sp. nov., are reported from the Republic flora, and three new species of the extinct genus Palaeocarpinus, Palaeocarpinus barksdaleae Pigg, Manchester & Wehr sp. nov., Palaeocarpinus stonebergae Pigg, Manchester & Wehr sp. nov., and Palaeocarpinus dentatus (Penhallow) Pigg, Manchester & Wehr comb. nov., are described from Republic, Washington; Princeton, British Columbia; and Stump Lake, British Columbia, respectively. Corylus johnsonii resembles three extant Asian species: Corylus wangii, Corylus ferox, and Corylus heterophylla. Involucres of this fossil species vary from being highly dissected and spiny like C. wangii and C. ferox to more laminar like C. heterophylla. This similarity is interesting because C. ferox and perhaps also C. wangii are members of section Acanthochlamys, thought to be basal within the genus. Carpinus perryae has asymmetric leaflike bracts that partly enclose an ovate nutlet and, thus, fits within the extant Carpinus subgenus Carpinus, a group with Asian, European, and North American affinities today. Palaeocarpinus, thought to be basal within the Coryloideae, is reported from several Eocene localities in the Okanogan Highlands. These occurrences demonstrate that this primarily Paleocene, extinct genus extended into the Eocene in western North America as it did in Asia. Associated staminate catkins containing coryloid pollen and Corylus‐like leaves also occur at Republic along with P. barksdaleae. The presence in the Okanogan Highlands floras of a suite of coryloid plants including both extinct and extant genera demonstrates that, like the birch subfamily Betuloideae, the subfamily Coryloideae was also a significant and diverse group in western North America during the middle Eocene.

Anatomically preserved Glossopteris foliage from the central Transantarctic Mountains

Abstract Two distinctive new species of Glossopteris, G. schopfii Pigg sp. nov., are described from the central Transantarctic Mountains, Antarctica. These new species represent the first species of Glossopteris based on internal anatomy. Glossopteris schopfii is characterized by narrow, elongate meshes, bundle sheath fibers, prominent phloem lacunae, papillar epidermal cells with straight margins and simple, longitudinally-oriented stomata. In contrast, G. skaarensis has broad polygonal meshes, a distinctive hypodermis, epidermal cells with sinuous margins and irregularly distributed, sunken stomata. These stomata are surrounded by a well-defined ring of subsidiary cells with beak-like papillae. The variety of anatomical detail demonstrated by these forms illustrates the diverse nature of glossopterid-bearing plants and underscores the value of permineralized peat to the study of Gondwana plants.

Anatomically preserved Liquidambar (Altingiaceae) from the middle Miocene of Yakima Canyon, Washington state, USA, and its biogeographic implications

Liquidambar changii Pigg, Ickert-Bond & Wen sp. nov. (Altingiaceae) is established for anatomically preserved, middle Miocene infructescences from Yakima Canyon, Washington, USA. Specimens are spherical, ∼2.5 cm in diameter, and have ∼25-30 tightly packed, bilocular fruits per head. Fruits are 3.4-4.7 mm wide × 2.6-3.5 mm long and wedge shaped, fused at the base, and free distally. Each locule contains 1-2 mature, elongate seeds proximally and 5-9 aborted seeds of more irregular shape distally. Mature seeds are 1.5 mm long × 1.2 mm wide, elongate, and triangular transversely, with a slight flange. Seeds have a seed coat for which three zones can be well defined, a uniseriate outer palisade layer, a middle region of isodiametric cells comprising most of the integument, and a uniseriate inner layer of tangentially elongate cells lining the embryo cavity. Liquidambar changii is most similar to the eastern Asian L. acalycina H.-T. Chang on features of infructescence, fruit, and seed morphology and quite unlike the North American L. styraciflua L. and other species. Such a close relationship between these two species supports a Beringian biogeographic track between eastern Asia and western North America during the Miocene. Previous phylogenetic and allozyme analysis of modern Liquidambar demonstrates a close relationship between North American-western Asian taxa and suggests a North Atlantic biogeographic track in the middle Miocene. Together, these biogeographic tracks underscore the complexity of the biogeographic history of the Altingiaceae in the Northern Hemisphere throughout the Neogene.