Paleobiochemistry of North American fossil Liriodendron sp.

Organic geochemical analyses are presented for a fossil Liriodendron sp. from the Miocene, Clarkia Flora of Northern Idaho. Flavonoid profiles determined for the fossil and two extent species of Liriodendron (L. chinense and L. tulipifera) confirm the generic status of the fossil material, but owing to a generic uniformity in flavonoid composition, fail to resolve taxonomic affinities at the species level. Steroid and other cycloalkane-alkene profiles indicate that the fossil taxon has a greater chemical similarity with L. chinense than L. tulipifera, despite the general leaf outline similarity between the fossil species and extent L. tulipifera. The morphologic and chemical data are interpreted as evidence for mosaic evolution within the genus, and the non-canalization of character states in some Miocene species.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF NORTH AMERICA: STIPULATE LEAVES OF THE RUBIACEAE INCLUDING A PROBABLE POLYPLOID POPULATION

A comparative study was made of the gross morphology, fine venation and cuticular features of Leitneria fioridana Chapman, the single living representative of the order Leitneriales and Leitneria eocenica (Berry) Brown, presumbaly a related fossil species. In addition to the type material, newly collected fossil specimens were investigated from clay pits in the Middle Eocene, Claiborne Formation, of western Tennessee and Kentucky. Foliate stipules attached to the petioles of several specimens suggest the assignment of this fossil leaf type to the genus Leitneria is incorrect. The nature of the gross morphology, fine venation and cuticular features confirms the misidentification. Previously, various specimens of this fossil leaf type have been placed in eight species of seven genera in seven families of six angiosperm orders, none of which are correct systematically. The gross morphology, venation and cuticular characters of the fossil leaf are distributed among a few extant South American genera of arborescent Rubiaceae. The fossil is an extinct rubiaceous leaf type which cannot be placed within a single modern subfamily, tribe or genus of the family. The organ genus, Paleorubiaceophyllum is proposed for these leaves. Three varieties of a single fossil species, P. eocenicum, are recognized. One variety with epidermal cells nearly twice the size of the others may represent a polyploid population.     

INTERCONNECTED REPRODUCTIVE AND VEGETATIVE REMAINS OF POPULUS (SALICACEAE) FROM THE MIDDLE EOCENE GREEN RIVER FORMATION,NORTHEASTERN UTAH

A new specimen from the Middle Eocene Evacuation Creek Member of the Green River Formation in northeastern Utah shows a twig with several leaves of Populus wilmattae Cockrell and a fruiting raceme attached. This specimen establishes for the first time the type of fruits borne by P. wilmattae and provides additional characters with which to assess its taxonomic and evolutionary status. An associated seed shows attached placental hairs like those of extant species of Populus. The Green River fossil differs from extant Populus species in having basically palmate leaf venation and in bearing its fruiting axis on a young twig. In other aspects, the fossil species is remarkably similar to the extant species Populus mexicana.     

鹅掌楸属(木兰科)次生木质部导管穿孔板的比较研究

利用扫描电子显微镜对鹅掌楸属仅存的2个自然种鹅掌楸和北美鹅掌楸的次生木质部导管穿孔板特征进行了详细的研究。结果显示,鹅掌楸属的2个种均以梯状穿孔板为主,同时存在网状-梯状混合穿孔板。鹅掌楸和北美鹅掌楸的导管穿孔板具有明显差异:(1)鹅掌楸具网状穿孔板,而北美鹅掌楸没有观察到;(2)北美鹅掌楸具单穿孔板,而鹅掌楸在该实验中未发现;(3)北美鹅掌楸具有横隔较粗的梯状穿孔板且横隔数目较多;(4)鹅掌楸的导管穿孔板多数横隔较少;(5)北美鹅掌楸的穿孔板倾斜角度较大;(6)北美鹅掌楸具麻黄式穿孔板的存在,且有纹孔膜残留存在。研究认为,北美鹅掌楸导管分子穿孔板分化较鹅掌楸更为剧烈。     

Comparative floral anatomy and ontogeny in Magnoliaceae

Floral anatomy and ontogeny are described in six species of Magnoliaceae, representing the two subfamilies Liriodendroideae (Liriodendron chinese and L. tulipifera) and Magnolioideae, including species with terminal flowers (Magnolia championi, M. delavayi, M. grandiflora, M. paenetalauma) and axillary flowers (Michelia crassipes). The sequence of initiation of floral organs is from proximal to distal. The three distinct outermost organs are initiated in sequence, but ultimately form a single whorl; thus their ontogeny is consistent with a tepal interpretation. Tepals are initiated in whorls, and the stamens and carpels are spirally arranged, though the androecium shows some intermediacy between a spiral and whorled arrangement. Carpels are entirely free from each other both at primordial stages and maturity. Ventral closure of the style ranges from open in Magnolia species examined to partially closed in Michelia crassipes and completely closed in Liriodendron, resulting in a reduced stigma surface. Thick-walled cells and tannins are present in all species except Michelia crassipes. Oil cells are normally present. Floral structure is relatively homogeneous in this family, although Liriodendron differs from other Magnoliaceae in that the carpels are entirely closed at maturity, resulting in a relatively small stigma, in contrast to the elongate stigma of most species of Magnolia. The flower of Magnolia does not terminate in an organ or organ whorl but achieves determinacy by gradual diminution.     

A new species of Zelkova (Ulmaceae,Ulmoideae) with leaves and fruits from the Oligocene of South China and its biogeographical implications

A new fossil species of Zelkova is described from the Oligocene Ningming Formation of Guangxi, South China. Zelkova ningmingensis sp. nov. is characterized by leaves with craspedodromous venation pattern and drupaceous fruit type. The new species possesses elliptical to ovate leaves, bearing 7–12 pairs of secondary and simple toothed margin, as well as epidermal cells with straight or rounded anticlinal walls. The species is compared with extant and other fossil species hitherto reported of the genus. It is most similar to the living Zelkova schneideriana in the leaf gross morphology and epidermal characters, which may be suggested to be the ancestral type of Zelkova schneideriana. The discovery of Zelkova ningmingensis sp. nov. in Guangxi indicates that Zelkova has already existed in southern China as early as the Oligocene. In combination with Zelkova material from the Oligocene of Europe, it can be inferred that Eurasian Zelkova had begun to diversify by at least the Oligocene. Because China is the biodiversity centre of modern Zelkova, the fossil herein provides new insights into Zelkova biogeography.     

福建中新世中期三宝木属(大戟科)一新种及其古气候与古生态学意义*

本文描述了发现于福建省漳浦地区佛昙群的三宝木属(Trigonostemon)一新种:漳浦三宝木(Trigonostemon zhangpuensis sp. nov. J.L. Dong et B.N. Sun)。该化石叶片呈倒披针形,基部窄,顶端渐尖;中上部的叶缘具细齿,近叶基1/3的部位全缘;叶脉为羽状环曲脉,中脉粗壮,向上逐渐变细;气孔器为无规则型,气孔呈长椭圆形,分布稀疏,无规则排列;平周壁不光滑,具褶皱。化石种与现生种剑叶三宝木(Trigonostemon xyphophyllorides(Croiz.) L.K. Dai et T.L. Wu)在叶片形态特征方面最为相似。剑叶三宝木分布在我国的海南省,基于化石种与最近亲缘现生种的生态幅基本一致的假设,漳浦地区在中新世中期的气候特征可能类似于现今海南省。化石种叶片上共划分13种损伤类型,属于6类功能性取食组,包括孔洞取食(hole feeding)、边缘取食(margin feeding)、留脉式取食(skeletonization)、表面取食(surface feeding)、造瘿(galling)和刺吸式取食(pierci...     

MOLECULAR DIVERGENCE BETWEEN ASIAN AND NORTH AMERICAN SPECIES OF LIRIODENDRON (MAGNOLIACEAE) WITH IMPLICATIONS FOR INTERPRETATION OF FOSSIL FLORAS

Botanists have long been aware of the floristic similarities between eastern Asia and eastern North America. Most who have considered this classic disjunction pattern have suggested that it arose through range disruption of a flora that was once more widely distributed in the Northern Hemisphere. There is less agreement on the timing of this process, with suggestions ranging from the Paleocene to the Neogene. In this study, molecular markers from two different plant genomes were used to assess the degree of genetic divergence between the two interfertile, morphologically similar species of the genus Liriodendron, i.e., L. tulipifera and L. chinense. Resulting molecular divergence estimates were translated into approximate dates of separation, independent of evidence from the fossil record. Allozyme data (Nei's genetic identity = 0.434) suggested a divergence time of 10–16 million years before present, whereas sequence divergence in the plastid genomes (1.24%) led to an estimate of approximately 11–14 million years before present. A review of the paleobotanical literature indicated that the fossil floras that included, or might have included Liriodendron could not have survived in Beringia after the late Miocene and the onset of southward-migrating Arctic air masses on the North American continent. This interpretation suggests a minimum time of separation of approximately 13 million years before present. Thus, both molecular data sets and the paleobotanical evidence concur in suggesting a divergence time of 10–16 million years before present. Interspecific compatibility and relative morphological stasis must have, therefore, persisted from at least the late Miocene. We emphasize the need for similar studies in other genera, especially those that have both a reasonable Tertiary fossil history and extant species in mesic temperate refugia in Asia, Europe, and western as well as eastern North America.     

Seasonal patterns of leaf water relations in four co-occurring forest tree species: Parameters from pressure-volume curves

Summary Leaf water relationships were studied in four widespread forest tree species (Ilex opaca Ait., Cornus florida L., Acer rubrum L., and Liriodendron tulipifera L.). The individuals studied all occurred on the same site and were selected to represent a range of growth forms and water relationships in some of the principal tree species of the region. The water relations of the species were analyzed using the concept of the water potential-water content relationship. The pressure-volume method was used to measure this relationship using leaf material sampled from naturally occurring plants in the field. Water potential components (turgor, osmotic, and matric) were obtained by analysis of the pressure-volume curves.Initial osmotic potentials (the value of the osmotic component at full turgidity) were highest (least negative) at the start of the growing season. They decreased (becoming progressively more negative) as the season progressed through a drought period. Following a period of precipitation at the end of the drought period, initial osmotic potentials increased toward the values measured earlier in the season.Seasonal osmotic adjustments were sufficient in all species to allow maintenance of leaf turgor through the season, with one exception: Acer appeared to undergo some midday turgor loss during the height of the July drought period.In addition to environmental influences, tissue stage of development played a role; young Ilex leaves had higher early season initial osmotic potentials than overwintering leaves from the same tree.The seasonal pattern of initial osmotic potential in Liriodendron and the observed pattern of leaf mortality suggested a possible role of osmotic potentials in the resistance of those leaves to drought conditions. The fraction of total leaf water which is available to affect osmotic potentials, called the osmotic water fraction in this study, was greatest in young tissue early in the season and declined as the season progressed.The results of this study showed that the water potential-water content relationship represents a dynamic mechanism by which plant internal water relations may vary in response to a changing external water-availability regime. The measured water relationships confirmed the relative positions of the species along a water-availability gradient, with Cornus at the wettest end and Ilex at the driest end of the gradient. Acer and Liriodendron were intermediate in their water relations. The spread of these species along a water-availability gradient on the same site suggested that coexistence is partially based on differential water use patterns.     

Fifteen polymorphic simple sequence repeat markers from expressed sequence tags of Liriodendron tulipifera

We developed and evaluated simple sequence repeat (SSR) markers derived from expressed sequence tags (ESTs) of Liriodendron tulipifera. Characteristics of 15 EST‐SSR loci were investigated using 33 L. tulipifera individuals. The number of alleles per locus ranged from two to five. The expected and observed heterozygosities ranged from 0.216 to 0.751 and from 0.182 to 0.97, respectively. These loci were further tested for their cross‐species transferability to Liriodendron Chinense. Because of their high level of polymorphism and transferability, our 15 single‐locus EST‐SSR markers will be valuable tools for research on mating system, population genetics and systemic evolution of Liriodendron.     

FOSSIL LEAVES OF DENDROPANAX FROM EOCENE SEDIMENTS OF SOUTHEASTERN NORTH AMERICA

As part of a reinvestigation of the Eocene floras from southeastern North America, a leaf form similar to some that were formerly placed in the genus Aradia has been identified as Dendropanax. Studies of the fine venation and cuticular characters have been important in this identification. This is the first report of leaf material of the genus Dendropanax in the fossil record.     

MUSOPSIS N. GEN.: A BANANA-LIKE LEAF GENUS FROM THE EARLY TERTIARY OF EASTERN NORTH GREENLAND

A fossil flora from the Late Paleocene-Early Eocene Thyra Ø Formation of eastern North Greenland (paleolatitude 77° N) has yielded monocotyledon leaf impressions with characters seen only in the closely related modem species in the families of Heliconiaceae, Musaceae, and Strelitziaceae. The combination of large costae widths and parallel, nonanastomosing, lateral veins that depart at right angles from the costae in the fossil material are features present only in leaves of extant species from these families. Three basic venation patterns also are recognized in the modem species of these families, but except for the genera Strelitzia and Phenakospermum, none of these patterns are present exclusively in any one family. Musopsis n. gen. is created for the fossil material from Greenland, but it is considered a form genus due to the lack of gross morphological features that can be used for separating leaves of the modem genera in Heliconiaceae, Musaceae, and Strelitiziaceae. It is the first known Arctic occurrence of fossil leaf material resembling this modem group of taxa.     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF SOUTHEASTERN NORTH AMERICA: PHILODENDRON LEAF REMAINS

Large leaves, new to the fossil record, from the Claiborne Formation in western Tennessee have been collected and analyzed. Careful analyses of venation and cuticular anatomy indicate that these fossil leaves contain specific characters found in modern species of the genus Philodendron subgenus Meconostigma. Features of venation were taxonomically more useful than other features. Reports of fossils of the Araceae are scarce and those few fossils assigned to the family frequently have been inadequately studied. This report establishes a reliable and carefully documented occurrence of the Araceae in the fossil record, and provides information concerning the differentiation of the family in time and the distributions of the genus Philodendron.     

Approaches to the identification of angiosperm leaf remains

During the past 125 years the history of early angiosperms, interpreted through the fossil leaf record has been largely an exercise in paleofloristic studies, ignoring evolution. Imprecise identifications of ancient leaves “matched” to extant genera and families have been used as the basis for reconstructions of paleocommunities and paleoclimates. However, as the result of careful morphological studies of leaf form, venation and cuticular features new insights into the evolution of angiosperms are now available. In this paper considerations are given to the usefulness and shortcomings of leaf form, venation and cuticular analysis as diagnostic tools of plant identification. Many techniques for the study of the morphology of modern and fossil leaves are included in this paper as well as tables outlining features of leaf venation and the epidermis. Careful morphological studies of leaf form (such as the venation and epidermal characters emphasized in this paper) will provide better understanding of the relationships of living angiosperms and transform the fossil leaf record into useful data that can be used to study the evolution of the angiosperms.     

Flavonoids of fossil miocene Platanus and its extant relatives

Flavonoids of seven extant Platanus species and a fossil Platanus species from the Miocene Clarkia Flora of northern Idaho were compared. Sixteen flavonoids were isolated of which 15 were either wholly or partially identified. Flavonoids of Platanus are based on kaempferol and quercetin and most glycosides are linked at position 3. Because of an extremely high degree of overall chemical similarity and the presence of minor variation within some species, flavonoid data were of limited value in clarifying relationships among extant species. Flavonoid data suggest a closer chemical similarity of the fossil Platanus species to the Asiatic P. orientalis, rather than to the six investigated North American species. Morphologically, however, the fossil Platanus is very similar to P.occidentalis from eastern North America. These findings are similar to those reported in a paleobiochemical study of a fossil Liriodendron species from the same Miocene Flora.     

Interspecies evolutionary divergence in <Emphasis Type="Italic">Liriodendron</Emphasis>, evidence from the nucleotide variations of <Emphasis Type="Italic">LcDHN-like</Emphasis> gene

Background

Liriodendron is a genus of Magnoliaceae, which consists of two relict species, Liriodendron chinense and L. tulipifera. Although the morphologies are highly similar, the two species exhibit different adaptive capacity. Dehydrins (DHNs) are abiotic stresses resistant proteins in planta, which are associated with adaptive evolution. To better understand the evolution divergence between L. chinense and L. tulipifera and how DHN genes are associated with adaptation evolution, we firstly investigated the DNA polymorphisms of the LcDHN-like gene in 21?L. chinense and 6?L. tulipifera populations.

Results

A 707?bp LcDHN-like gene was cloned, which included a 477?bp open reading frame (ORF) and coding 158 amino acids. 311 LcDHN-like gDNA sequences were obtained from 70?L. chinense and 35?L. tulipifera individuals. The AMOVA and phylogenetic relationship analysis showed significant differences between the two species. A higher genetic diversity was observed in L. tulipifera compared to L. chinense, in consistent with the higher adaptive capacity of L. tulipifera. Our data also suggested that the LcDHN-like genes’ polymorphisms were under neutral mutation and purifying selection model in the L. chinense and L. tulipifera populations, respectively. The distinct expanding range and rate between the two species, haplotypes shared only in L.chinense’s nearby populations, and wide dispersals in L. tulipifera could contribute to the obscure east-west separation in L. chinense and entirely unordered phylogeny in L. tulipifera. The completely separated nonsynonymous substitution at position 875 and the higher range scope of aliphatic index in L. tulipifera populations may be related with its higher adaptive capacity. Taken together, our study suggests LcDHN-like gene is a potential mark gene responsible for adaptive evolution divergence in Liriodendron.

Conclusions

Significant differences and completely distinct haplogroups between L. chinense and L. tulipifera showed that the two species have evolved into different directions. The more widely distribution, earlier haplogroups divergence events, and richer SNPs variations in L. tulipifera could imply its stronger adaptation in this species. And potential effect of the allelic variations in LcDHN-like gene may reflect the difference of water stress and chill tolerance between L. chinense and L. tulipifera, which could provide some information for further adaption evolution studies of Liriodendron.

     

The new species Ettingshausenia sarbaensis (Angiospermae) from the Cenomanian-Turonian of Western Kazakhstan in light of the problem of classification of dispersed cretaceous Platanus-like leaves

Based on morphological and epidermal characters of the leaf, a new species, Ettingshausenia sarbaensis sp. nov., from the Cenomanian-Turonian of western Kazakhstan is described. In fossil Platanus-like leaves, the unique epidermal structure, with the combination of encyclocytic, laterocytic, and paracytic stomata and the presence of trichomes on one or from two to seven epidermal cells, is shown for the first time. Based on variations in morphological and epidermal characters, two morphotypes corresponding to groups of sun and shade leaves are recognized. The expediency of consideration of dispersed Cretaceous Platanus-like leaves within the framework of morphological classification of leaves is discussed.     

COMPARATIVE PALEOBIOCHEMISTRY OF SOME FOSSIL AND EXTANT FAGACEAE

A Fagus-like leaf fossil (cuticular compression) with an attached fruit, differing from any known Fagus species (fossil or extant) or other fagoid taxa, has been discovered from the Miocene Clarkia Lake deposits of northern Idaho. Because of its unusual morphology (especially the fruit) the fossil taxon has been described as a new genus and species, Pseudofagus idahoensis Smiley and Huggins. The successful previous use of paleobiochemistry in studies of fossil taxa from the Miocene Succor Creek Flora of Oregon suggested that chemical data might help clarify the taxonomic affinities of Pseudofagus. Indeed, examination of the chemistry of the fossil, Pseudofagus idahoensis, and comparison with extant Fagus species and related fagoid genera indicate that: 1) based on steroid chemistry, Pseudofagus idahonesis does belong in the Fagaceae; 2) like all extant species of Fagus, the fossil lacks the tannin component, ellagic acid, which separates it from other extant fagoid genera, and 3) its simple flavonoid pigment profile places it closest to the extant North American Fagus grandifolia or the European/Eurasian Fagus sylvatica. However, the exclusive presence of an isorhamnetin (3'-methoxyquercetin) 3-0-glycoside, onocerane, and 5α-cholestane imparts a species-specific chemical character to Pseudofagus idahoensis, which also sets it apart from extant species of Fagus. While the chemistry does not decide the taxonomic level to be accorded to the fossil, it certainly supports, along with morphology and anatomy, the distinctness of Pseudofagus and its proposed relationships within the Fagaceae.     

Germination and early growth of <Emphasis Type="Italic">Ailanthus</Emphasis> and tulip poplar in three levels of forest disturbance

Increasing rates of forest disturbance may provide greater opportunity for invasion of nonnative species, thereby altering the successional trajectory of native plant communities. In the eastern U.S., invasive Ailanthus altissima and native Liriodendron tulipifera have similar life histories and niches and often co-occur. To examine how disturbance affects the establishment of these species, we performed field experiments to evaluate the response of sown seeds and transplanted seedlings to three levels of disturbance on north- and south-facing aspects. L.␣tulipifera germination was severely limited by low seed viability and had significantly lower germination than A. altissima in all sites. The effect of disturbance regime on A. altissima germination depended on aspect in the second growing season. In contrast, mean seedling survival, biomass, leaf area and leaf area ratio were greater for L. tulipifera in all field sites. Overall, the north-facing selective cut forest provided a disproportionately large number of suitable microsites for L. tulipifera establishment. Collectively, this study demonstrated that different timber harvest practices produce heterogeneous mosaics of suitable microsites for germination and establishment. Limited L. tulipifera germination may be a serious constraint to population establishment if seeds are deposited for the first time immediately after a disturbance event. However, if sufficient viable seeds of both species exist, L. tulipifera out-performs the invasive in the first two years following disturbance. This may explain why A. altissima has shown explosive population growth in a limited number of sites in the past century.     

Resource–consumer diversity: testing the effects of leaf litter species diversity on stream macroinvertebrate communities

1. Understanding relationships between resource and consumer diversity is essential to predicting how changes in resource diversity might affect several trophic levels and overall ecosystem functioning. 2. We tested for the effects of leaf litter species diversity (i.e. litter mixing) on litter mass remaining and macroinvertebrate communities (taxon diversity, abundance and biomass) during breakdown in a detritus‐based headwater stream (North Carolina, U.S.A.). We used full‐factorial analyses of single‐ and mixed‐species litter from dominant riparian tree species with distinct leaf chemistries [red maple (Acer rubrum), tulip poplar (Liriodendron tulipifera), chestnut oak (Quercus prinus) and rhododendron (Rhododendron maximum)] to test for additivity (single‐species litter presence/absence effects) and non‐additivity (emergent effects of litter species interactions). 3. Significant non‐additive effects of litter mixing on litter mass remaining were explained by species composition, but not richness, and litter‐mixing effects were variable throughout breakdown. Specifically, small differences in observed versus expected litter mass remaining were measured on day 14; whereas observed litter mass remaining in mixed‐species leaf packs was significantly higher on day 70 and lower on day 118 than expected from data for single‐species leaf packs. 4. Litter mixing had non‐additive effects on macroinvertebrate community structure. The number of species in litter mixtures (two to four), but not litter species composition, was a significant predictor of the dominance of particular macroinvertebrates (i.e. indicator taxa) within mixed‐species packs. 5. In addition, the presence/absence of high‐ (L. tulipifera) and low‐quality (R. maximum) litter had additive effects on macroinvertebrate taxon richness, abundance and biomass. The presence of L. tulipifera litter had both positive (synergistic) and negative (antagonistic) effects on invertebrate taxon richness, that varied during breakdown but were not related to litter chemistry. In contrast, the presence/absence of L. tulipifera had a negative relationship with total macroinvertebrate biomass (due to low leaf mass remaining when L. tulipifera was present and higher condensed and hydrolysable tannins associated with leaf packs lacking L. tulipifera). Macroinvertebrate abundance was consistently lower when R. maximum was present, which was partially explained by litter chemistry [e.g., high concentrations of lignin, condensed tannins, hydrolysable tannins and total phenolics and high carbon to nutrient (N and P) ratios]. 6. The bottom‐up effects of litter species diversity on stream macroinvertebrates and litter breakdown are different, which suggests that structural attributes of macroinvertebrate communities may only partially explain the effects of litter‐mixing on organic matter processing in streams. In addition, stream macroinvertebrates colonising decomposing litter are influenced by resource diversity as well as resource availability. Broad‐scale shifts in riparian tree species composition will alter litter inputs to streams, and our results suggest that changes in the diversity and availability of terrestrial litter may alter stream food webs and organic matter processing.