Princeton Chert Research Articles

Fossil Coryphoid Palms from the Eocene of Vancouver, British Columbia

Premise of research. Fossil fan palm fronds are well known from Eocene sites in the United States; however, although they are also known from the Paleogene Huntingdon Formation of British Columbia for over 100 years, these are poorly studied. There are early anecdotal reports of Eocene “Sabal” or Sabalites leaves from the Vancouver area, pollen from Vancouver and the interior of British Columbia, and a single megafossil palm described from the Princeton Chert, indicating past warm climates in the region. Leaves of coryphoid palms (Arecaceae) from British Columbia are described formally here for the first time.Methodology. We analyze morphologically the Eocene palm frond fossils from the Vancouver area (Huntingdon Formation) and the Ashcroft area in British Columbia.Pivotal results. The Sabalites fossil fronds from the Vancouver area represent fan palms (subfamily Coryphoideae, cf. tribe Sabaleae) and are assigned to the new taxon Sabalites dawsonii. These and other Eocene palm fossils from the Pacific Northwest demonstrate that—based on prior paleoclimate analyses—coryphoid palms were growing under paleotemperatures close to their modern cold limits. Palm fossils reported from near Ashcroft are not Arecaceae, as key diagnostic characters are absent.Conclusions. These and comparable palm fossil records, coupled with analyses of paleoclimate, corroborate an early Paleogene origin of temperate climate adaptation by Coryphoideae, likely as part of the initial Sabaleae and Trachycarpeae diversifications.

An Eocene tar spot on a fossil palm and its fungal hyperparasite

Two ascomycetes from the middle Eocene (48.7 million yr b.p.) Princeton chert are described. Palaeoserenomyces allenbyensis gen. et sp. nov. consists of long, loculate stromata of distinctive columnar cells beneath the epidermis of the extinct fan palm, Uhlia allenbyensis. The sporogenous locules are emp- ty but stromatal features and locule shape are similar to extant Serenomyces, a genus in the Phyllachorales that forms leaf spots on coryphoid palms. The locules of P allenbyensis contain circular structures that are interpreted as intralocular ascomata of a mycoparas- ite, Cryptodidymosphaerites princetonensis gen. et sp. nov. Two-celled ascospores in uniseriate rows are sim- ilar to the genus Didymosphaeria of the Melanom- matales. These fossils are compared to Didymosphaer- ia conoidea, an extant mycoparasite of stromatic as- comycetes. The large number of exquisitely pre- served fungal structures on taxonomically defined hosts in the Princeton chert provides a unique op-

Cretaceous and Paleogene Fagaceae from North America and Greenland: evidence for a Late Cretaceous split between Fagus and the remaining Fagaceae

Abstract Modern lineages of the beech family, Fagaceae, one of the most important north-temperate families of woody flowering plants, have been traced back to the early Eocene. In contrast, molecular differentiation patterns indicate that the Fagus lineage, Fagoideae, with a single modern genus, evolved much earlier than the remaining lineages within Fagaceae (Trigonobalanoideae, Castaneoideae, Quercoideae). The minimum age for this primary split in the Fagaceae has been estimated as 80 ± 20 Ma (i.e. Late Cretaceous) in recently published, time-calibrated phylogenetic trees including all Fagales. Here, we report fagaceous fossils from the Campanian of Wyoming (82-81 Ma; Eagle Formation [Fm]), the Danian of western Greenland (64-62 Ma; Agatdal Fm), and the middle Eocene of British Columbia (ca 48 Ma; Princeton Chert), and compare them to the Fagaceae diversity of the recently studied middle Eocene Hareøen Fm of western Greenland (42-40 Ma). The studied assemblages confirm that the Fagus lineage (= Fagoideae) and the remainder of modern Fagaceae were diverged by the middle Late Cretaceous, together with the extinct Fagaceae lineage(s) of Eotrigonobalanus and the newly recognised genus Paraquercus, a unique pollen morph with similarities to both Eotrigonobalanus and Quercus. The new records push back the origin of (modern) Fagus by 10 Ma and that of the earliest Fagoideae by 30 Ma. The earliest Fagoideae pollen from the Campanian of North America differs from its single modern genus Fagus by its markedly thicker pollen wall, a feature also seen in fossil and extant Castaneoideae. This suggests that a thick type 1 foot layer is also the plesiomorphic feature in Fagoideae although not seen in any of its living representatives. The Danian Fagus pollen of Greenland differs in size from those of modern species but is highly similar to that of the western North American early Eocene F. langevinii, the oldest known beech so far. Together with the Quercus pollen record, absent in the Campanian and Danian formations but represented by several types by the middle Eocene, this confirms recent dating estimates focussing on the genera Fagus and Quercus, while rejecting estimates from all-Fagales-dated trees as too young. The basic Castaneoideae pollen type, still found in species of all five extant genera of this putatively paraphyletic subfamily, represents the ancestral pollen type of most (modern) Fagaceae (Trigonobalanoideae, Castaneoideae, Quercoideae).

A review of the plants of the Princeton chert (Eocene, British Columbia, Canada)

The Princeton chert is one of the most completely studied permineralized floras of the Paleogene. Remains of over 30 plant taxa have been described in detail, along with a diverse assemblage of fungi that document a variety of ecological interactions with plants. As a flora of the Okanagan Highlands, the Princeton chert plants are an assemblage of higher elevation taxa of the latest early to earliest middle Eocene, with some components similar to those in the related compression floras. However, like the well-known floras of Clarno, Appian Way, the London Clay, and Messel, the Princeton chert provides an additional dimension of internal structure. In the present study, we outline the history of Princeton chert plant research, starting with Boneham and others, and extending into studies by Stockey and her students and colleagues. These studies were undertaken primarily at the University of Alberta, Edmonton. We then re-examine the individual elements of the Princeton chert flora, using the framework of the currently recognized Angiosperm Phylogeny Group (APG III) phylogeny and in light of recent fossil discoveries. We hope that this update will bring to mind new aspects of the significance of the Princeton chert flora to Paleogene paleobiology, biogeography, and plant evolution.

Paleomycology of the Princeton Chert. III. Dictyosporic microfungi, Monodictysporites princetonensis gen. et sp. nov., associated with decayed rhizomes of an Eocene semi-aquatic fern

This study builds on previous investigations of paleomycological diversity within permineralized plants of a significant Eocene paleobotanical locality, the Princeton Chert. The fungal body fossils described here occur in decayed rhizomes of the extinct semi-aquatic fern Dennstaedtiopsis aerenchymata. Fungi include vegetative hyphae throughout the plant tissue, as well as a dense assemblage of >100 dematiaceous spores. The spores occur in a discrete zone surrounding two extraneous rootlets of other plants, which penetrated the fern tissue post-mortem. Spores are obovoid and muriform, composed of 8–12 cells with constricted septa and produced from hyaline or slightly pigmented hyphae. The spores are morphologically similar to both asexual reproductive dictyospores of phylogenetically disparate microfungi attributed to the morphogenus Monodictys and perennating dictyochlamydospores that occur in the anamorph genus Phoma. In addition to expanding the early Eocene fossil record for Ascomycota, these specimens also provide new insight into the rapidity of initial phases of the fossilization process in this important paleobotanical locality.

A review of paleobotanical studies of the Early Eocene Okanagan (Okanogan) Highlands floras of British Columbia, Canada, and Washington, USA

The history of plant fossil collecting in the Okanagan (Okanogan) Highlands of British Columbia and northeastern Washington is closely intertwined with the history of geological surveys and mining activities from the 1870s onward. The first descriptions of fossil plants from British Columbia were published in 1870–1920 by J.W. Dawson, G.M. Dawson, and D.P. Penhallow. In the United States, fossil leaves and fish were first recognized at Republic, Washington, by miners in the early 1900s. Many early workers considered these floras to be of Oligocene or Miocene age. C.A. Arnold described Canadian occurrences of conifers and Azolla in the 1950s. Palynological studies in the 1960s by L.V. Hills, G.E. Rouse, and others and those of fossil fish by M.V.H. Wilson in the 1970–1980s provided the framework for paleobotanical research at several key localities. Permineralized plants were first described from the Princeton chert in the 1970s by C.N. Miller, J.F. Basinger, and others, followed by R.A. Stockey and her students. W.C. Wehr and K.R. Johnson revitalized the study of fossils at Republic with the discovery of a diverse assemblage in 1977. In 1987, J.A. Wolfe and Wehr produced a United States Geological Survey monograph on Republic, and Wehr cofounded the Stonerose Interpretive Center as a venue for public collecting. Systematic studies of the Okanagan Highlands plants, as well as paleoecological and paleoclimate reconstructions from palynomorphs and leaf floras, continue to expand our understanding of this important Early Eocene assemblage.

Characterization of the stem anatomy of the Eocene fern Dennstaedtiopsis aerenchymata (Dennstaedtiaceae) by use of confocal laser scanning microscopy

Permineralization provides the most faithful known mode of three-dimensional preservation of the morphology and cellular anatomy of fossil plants. Standard optical microscopic documentation of such structures can provide only an approximation of their true three-dimensional form and is incapable of revealing fine-structural (<300 nm) details, deficiencies that can be addressed by the use of confocal laser scanning microscopy (CLSM). To demonstrate the usefulness of CLSM in such studies, we compare confocal laser scanning micrographs and optical photomicrographs of the permineralized tissues of rhizomes and petioles of the Eocene fern Dennstaedtiopsis aerenchymata preserved in cherts of the Clarno Formation of Oregon, USA, and the Allenby Formation (Princeton chert) of British Columbia, Canada. The laser-induced fluorescence detected by CLSM produces crisp high-resolution images of the three-dimensionally permineralized tissues of Dennstaedtiopsis aerenchymata. Tissues analyzed include the epidermis and epidermal hairs, cortex, aerenchyma, endodermis, vascular tissue, and pith-for each of which, CLSM yields results superior to those of standard optical microscopy. CLSM and previous Raman spectroscopic analyses of the same specimens provide evidence consistent with original biochemistry. Use of CLSM to characterize the morphology and cellular anatomy of permineralized fossil plants can provide accurate data in two and three dimensions at high spatial resolution, information that can be critically important to taxonomic, taphonomic, and developmental interpretations. Results presented here from this first detailed CLSM-based study of permineralized plant axes indicate that this nonintrusive, nondestructive technique should be widely applicable in paleobotany.

Paleomycology of the Princeton Chert I. Fossil hyphomycetes associated with the early Eocene aquatic angiosperm, Eorhiza arnoldii

The Eocene (~ 48.7 Ma, Ypresian–Lutetian) Princeton Chert of British Columbia, Canada, has long been recognized as a significant paleobotanical locality, and a diverse assemblage of anatomically preserved fossil plants has been extensively documented. Co-occurring fossil fungi also have been observed, but the full scope of their diversity has yet to be comprehensively assessed. Here, we present the first of a series of investigations of fossilized fungi associated with the silicified plants of the Princeton Chert. This report focuses on saprotrophic, facultative-aquatic hyphomycetes observed in cortical aerenchyma tissue of an enigmatic angiosperm, Eorhiza arnoldii. Our use of paleontological thin sections provides the opportunity to observe and infer developmental features, making it possible to more accurately attribute two hyphomycetes that were observed in previous studies. These comprise multiseptate, holothallic, chlamydospore-like phragmoconidia most similar to extant Xylomyces giganteus and basipetal phragmospore-like chains of amerospores like those of extant Thielaviopsis basicola. We also describe a third hyphomycete that previously has not been recognized from this locality; biseptate, chlamydosporic phragmoconidia are distinguished by darkly melanized, inflated apical cells and are morphologically similar to Brachysporiella rhizoidea or Culcitalna achraspora.

The First Organismal Concept for an Extinct Species of Pinaceae:Pinus arnoldiiMiller

The Eocene Princeton Chert locality of southern British Columbia, Canada, provides data to develop organismal concepts for several species of fossil plants, including the first extinct species of Pinaceae, Pinus arnoldii Miller. This new species concept is based on a combination of interconnected organs, common histological features, and patterns of association among isolated plant parts. These data expand our knowledge of P. arnoldii from a morphospecies of ovulate cones to an extinct species of pine that produces woody stems with five-needled fascicles of leaves; simple pollen cones with two abaxial pollen sacs per microsporophyll, containing bisaccate pollen grains; seed cones with inflated scale apices, dorsal umbos that do not bear mucros, and a thick-walled sclerotic outer cortex; and coralloid roots with ectomycorrhizal associations. Organs preserved at various stages of development provide evidence for numerous aspects of growth and reproductive biology, including pollination biology and seed cone development. Cladistic analyses of morphological and molecular characters demonstrate that the novel combination of characters displayed by P. arnoldii causes this extinct species to fall near the base of the Pinus L. tree, either as the sister to all living species of the subgenus Pinus or outside the subgenera that have been defined by extant species of Pinus.

Cyclic sedimentation in the Eocene Allenby Formation of south-central British Columbia and the origin of the Princeton Chert fossil beds

Extensive deposits of Eocene conglomerate, sandstone, shale, and sub-bituminous coal occur within a half-graben at Princeton, British Columbia. These strata comprise ∼2000 m of fluvial sediment interbedded with tephra and volcanic flows. Near the southeast margin of the basin, ∼200 m of rhythmically bedded strata are exposed along the Similkameen River. Cyclic deposition resulted from repeated episodes of hydrologic and topographic change related to seismic activity along the Boundary Fault on the east flank of the Princeton Basin, where Allenby Formation sediments are juxtaposed against metamorphic and metavolcanic rocks of the Upper Triassic Nicola Group. Interbedded carbonaceous shale and tuffaceous sandstone record influxes of distal lahar deposits into a lowland swamp. Coal–breccia transitions originated when debris flows along the scarp carried volcanic debris into adjacent wetlands. Coal–chert rhythmites are inferred to be evidence of hydrologic changes associated with floodplain tilt events that caused lowland to repeatedly alternate between a stagnant pond (“fen”) and a stream-fed lake. During fen stages, peat was silicified in situ from percolation of groundwater carrying silica dissolved from underlying tuffaceous beds. Episodic influxes of stream flow reduced dissolved silica concentrations and caused increases in dissolved oxygen levels. These geochemical changes caused organic matter that accumulated during these conditions of open water circulation to remain unsilicified and susceptible to partial maceration. Diagenesis eventually converted these deposits to alternating beds of sub-bituminous coal intercalated with chert horizons.

Anatomy and development of fruits of Lauraceae from the Middle Eocene Princeton Chert

Investigations of the Middle Eocene Princeton Chert reveal evidence for the connection of lauraceous flowers to fruits through a developmental series. Youngest fruits are found with attached floral remnants. Later stages show receptacle enlargement, fruit wall thickening, and the development of abundant sclereid clusters. Mature fruits are borne on a shallow receptacle and have an endocarp palisade layer of radially elongate cells with stellate outlines, an inner mesocarp layer of radiately arranged sclereid clusters, and a fleshy outer mesocarp layer containing numerous idioblasts with contents. Each mature fruit bears a single seed retaining the outer integument with an innermost radially elongate transfusion cell layer. Mature seeds contain a cellular embryo bearing idioblasts. Fruits are distinguishable from previously described anatomically preserved fossil taxa. This study represents the only documented developmental reconstruction of fossil fruits of Lauraceae and that self-pruning evolved prior to the Eocene. Anatomical modifications over the developmental sequence indicate that different stages of maturity preserved together, may be erroneously identified as several taxa at a fossil locality. Fossil morphotypes typically underestimate species number, but this study suggests that the number of inferred species based on fruit types may be inflated for Lauraceae, potentially exaggerating the tropical interpretation of the paleoenvironment.

Establishing a fossil record for the perianthless Piperales: Saururus tuckerae sp. nov. (Saururaceae) from the Middle Eocene Princeton Chert

Investigations of small permineralized flowers from the Middle Eocene Princeton Chert, British Columbia, Canada have revealed that they represent an extinct species of Saururus. Over 100 flowers and one partial inflorescence were studied, and numerous minute perianthless flowers are borne in an indeterminate raceme. Each flower is subtended by a bract, and flowers and bracts are borne at the end of a common stalk. Five stamens are basally adnate to the carpels. Pollen is frequently found in situ in the anthers. Examined under SEM and TEM, pollen grains are minute (6-11 μm), monosulcate, boat-shaped-elliptic, with punctate sculpturing and a granulate aperture membrane. The gynoecium is composed of four basally connate, lobed carpels with recurved styles and a single ovule per carpel. Flower structure and pollen are indicative of Saururaceae (Piperales), and in phylogenetic analyses using morphological characters, the fossils are sister to extant Saururus. The fossil flowers are described here as Saururus tuckerae sp. nov. These fossil specimens add to the otherwise sparse fossil record of Piperales, represent the oldest fossils of Saururaceae as well as the first North American fossil specimens of this family, and provide the first evidence of saururaceous pollen in the fossil record.

Susiea newsalemaegen. et sp. nov. (Nymphaeaceae):Euryale‐like Seeds from the Late Paleocene Almont Flora, North Dakota, U.S.A.

Susiea newsalemae Taylor, DeVore & Pigg gen. et sp. nov. is described for distinctive seeds referable to the water lily family Nymphaeaceae from the Late Paleocene Almont Flora of central North Dakota, U.S.A. Seeds are oval to barrel shaped, 5 mm $$\mathrm{long}\,\times 3$$ mm wide, and have an apical operculum and a prominent lateral raphe. The outer surface of the seeds is composed of palisade, shinglelike cells 40 μm $$\mathrm{high}\,\times 150$$ μm wide with smooth cell margins lacking papillae. The operculum is 1 mm across and surrounded by a narrow furrow, covering the micropyle but not the hilum. The raphe and micropyle are separated by several cells. Several specimens have a small embryo cavity surrounded by a small area of presumed endosperm below the micropyle and a well‐developed perisperm filling the rest of the seed cavity. Susiea seeds are most similar to those of extant Euryale but differ in features of the epidermal cells, seed coat, and raphe morphology. They also share some features with Nymphaea, Nuphar, and Victoria. Susiea appears distinct from the permineralized fossil seeds of the middle Eocene Allenbya from the Princeton chert, Nuphar wutuensis from the Eocene of China, and Nuphar cf. wutuensis from the same Almont beds. Susiea is the oldest fossil taxon of the Euryale lineage, extending the previous Oligocene record back to the Late Paleocene and documenting a significantly older age for the Euryale/Victoria clade that is clearly a derived lineage based on phylogenetic analyses of modern taxa.

Trawetsia princetonensis gen. et sp. nov. (Blechnaceae): A Permineralized Fern from the Middle Eocene Princeton Chert

Trawetsia princetonensis Smith, Stockey, Nishida & Rothwell gen. et sp. nov. is described from several permineralized rhizomes, stipes, and higher‐order frond members of a blechnoid fern that have been identified from the Middle Eocene Princeton Chert of British Columbia. Rhizomes bear stipes arising from all sides of the stem as well as diarch adventitious roots. The dictyostelic rhizomes are up to 16 mm across and have five to seven amphiphloic cauline bundles that are capped internally and externally by sclerenchyma. Ground tissue, where well preserved, is transitional from arenchymatous to parenchymatous, with abundant small sclerotic nests found throughout the pith and cortex. Multicellular scales are borne on the rhizome but are sparse and do not imbricate. At least three orders of frond material are preserved: stipes, primary pinnae, and laminar pinnules. Stipes have an adaxial groove, two adaxial hippocampiform bundles, and seven or fewer small, circular bundles arranged in an abaxial U‐shaped arc...

Evidence for Sympodial Vascular Architecture in a Filicalean Fern Rhizome: Dickwhitea allenbyensis gen. et sp. nov. (Athyriaceae)

A new genus and species of anatomically preserved fossil filicalean ferns Dickwhitea allenbyensis gen. et sp. nov. is described from the Middle Eocene Princeton Chert of southern British Columbia, Canada. Rhizomes have a parenchymatous pith surrounded by a ring of five amphiphloic cauline bundles and pairs of frond traces that diverge from adjacent cauline bundles in a 2/5 phyllotaxis. The cortex is also parenchymatous except at the periphery, where there is a well‐developed sclerotic hypodermis. The stipe is characterized by a pair of hippocampiform bundles, and ground tissues are similar to those of the rhizome. Prominent nests of large cells with black contents occur adjacent to the vascular bundles in the ground tissue of the rhizome and stipe. Roots are diarch with cortex that grades from parenchymatous at the interior to sclerotic at the periphery. The vascular architecture of this fern appears to be novel among known Filicales. There are no gaps in the stele that result from the divergence of either frond or root traces, and there is no evidence that cauline bundles anastomose. Rather, the cauline bundles extend through the rhizome independently of each other, with each cauline bundle producing successive frond traces on alternating tangents. Root traces diverge from the outer surface of cauline bundles as is characteristic of solenostelic filicalean species and dictyostelic tree ferns. Examination of the literature reveals that there is a wide range of variation in filicalean vascular architectures that traditionally has not been recognized. Although there is anecdotal evidence that this newly recognized stelar variation is correlated with patterns of systematic diversity, the overall phylogenetic significance of fern vascular architecture has yet to be fully explored.

Pinus baileyi (section Pinus, Pinaceae) from the Paleogene of Idaho, USA

Pinus baileyi from the Paleogene of Idaho was initially related to the bristlecone pine P. longaeva (subgen. Strobus, sect. Parrya, subsect. Balfourianae) from western North America. Unlike the centromucronate condition in P. longaeva, P. baileyi cones have raised umbos that are excentromucronate, i.e., the mucro positioned in the upper umbo field above the keel. Cone size and scale morphology shows that P. baileyi more closely resembles excentromucronate pines of subsects. Halepenses and Pinus sensu Gernandt et al. (2005, Taxon 54: 29-42), but is most similar to P. resinosa, P. kesiya, and P. massoniana of subsect. Pinus. Morphologically, P. baileyi resembles the fossil species P. princetonensis and P. arnoldii from the Eocene Princeton Chert, British Columbia, Canada. Pinus baileyi extends the western North American range of ovulate cones resembling subsect. Pinus from the middle Eocene of British Columbia, Canada and Washington, USA to the Oligocene of Idaho, USA. Pinus baileyi, and possibly P. princetonensis and P. arnoldii, indicates the presence of early populations of subsect. Pinus-type pines in the western cordillera of North America, raising the possibility that P. resinosa and P. tropicalis may have evolved from this group.

Morphogenesis of the Specialized Peridermal Tissues in Decodon Allenbyensis from the Middle Eocene Princeton Chert

Aquatic tissues in the submerged axes of Decodon allenbyensis Cevallos- Ferriz et Stockey are investigated and described in detail. Numerous well-preserved roots have primary aerenchymatous cortex and no secondary vascular tissues while other axes show transitions to secondary xylem and phloem, as well as periderm composed of thin-walled lacunate phellem. Phellem appears similar to the primary aerenchyma seen in aquatic roots of species of Ludwigia L.; however, similar lacunate tissue in extant Decodon verticillatus (L.) Ell. is secondary (phellem) and this study shows this tissue to be homologous to that seen in the fossil Decodon J.F. Gmel. A complex rhytidome is described in the largest fossil axes. It is composed of alternating bands of 'phelloids' and bands of non-active phloem with lacunae. This complex aquatic rhytidome is currently unknown in other living or fossil taxa.

The Fossil Record of Basal Monocots

The fossil record of basal monocots (Acorales and Alismatales) extends back to the Cretaceous in the Northern Hemisphere. While many fossils were originally assigned to these basal groups, rigorous paleobotanical studies show many of them to be misidentified. Acorus fossils have been reliably reported from the Eocene while those of Alismatales extend back to the early Cretaceous. The fossil record of basal monocots is usually represented by leaves, fruits, and seeds; however, some localities preserve stems with attached leaves and roots and even whole plants. A detailed examination of leaf venation patterns in alismatids has recently allowed the description of a new taxon from the Upper Cretaceous of Alberta based on leaves attributed to Limnocharitaceae. Anatomically preserved alismatid petioles (Heleophyton helobiaeoides) and well-preserved flowers/fruits are known from the Middle Eocene Princeton chert of British Columbia. A complete developmental sequence from flower to fruit is known, and this material has good possibilities for whole plant reconstruction. The extinct floating aquatic Limnobiophyllum (Araceae/Lemnoideae) and the genus have been the subject of morphological cladistie analyses and competing hypotheses of relationships among aroids and duckweeds. The fossil record and recent molecular studies support separate origins of and the duckweeds from within Araceae. The fossil taxon Pistia corrugata has origins of and the of new evidence and indicates the presence of a new genus that shows leaf morphology unlike that seen in extant Pistia, but with a similar growth habit. Fossil evidence indicates morphology unlike that habit probably arose at least three times within Araceae.

Duabanga-like leaves from the Middle Eocene Princeton chert and comparative leaf histology of Lythraceae sensu lato

A permineralized lythraceous leaf type found in close association with fruits, stems, and roots of Decodon allenbyensis Cevallos-Ferriz et Stockey in the Middle Eocene Princeton chert of British Columbia, Canada, is described. Midribs have a prominent C-shaped midvein surrounded by sclerenchyma, with an adaxial epidermis of rectangular to rounded cells lacking enlarged mucilage cells. Leaves are dorsiventral, 180-270 μm thick at the lamina, with a double palisade layer. Abaxial epidermal cells have prominent papillae, and these epidermal cells can be infected by fungi, forming dark sterile stromata. Fossil leaves are similar to those of Myrtales and are compared to those of Lythraceae sensu lato. Although these leaves are thought to belong to the previously described Decodon allenbyensis found in the same chert layer, they lack the diagnostic features of extant Decodon leaves. Instead they share most anatomical similarities with Duabanga grandiflora Roxburgh ex DC Walpers (Lythraceae, subfamily Duabangoideae) including vascular tissues, palisade and spongy mesophyll, bundle fibers, and abaxial epidermal papillae. Duabanga grandiflora differs from the fossil in having mucilaginous cells and a consistently V-shaped abaxial midrib. Although anatomically similar to Duabanga, the fossil leaves are considered those of D. allenbyensis, based on association and the depositional environment prior to preservation. Recent phylogenetic analyses place Duabanga and Decodon in separate clades within Lythraceae, but relationships between these clades are not well supported, indicating that fossil leaves should provide useful anatomical characters for elucidating relationships within Lythraceae.

Contributions of Permineralized Plant Fossils to Plant Morphology

Summary: Permineralization is a peculiar process of fossilization preserving anatomical details of plants of the Past, in some cases with a remarkable condition as represented by motile sperm in an Permian ovule. Here I introduce selected studies on permineralized plant remains emphasizing their importance in plant morphological studies to various extent. Ferns from the Eocene Princeton Chert Bed, Canada, Late Cretaceous plants from Japan, and a megasporangiate organ of Late Permian Glossopteris from Australia are mentioned.