A Study on the Morphology of Foliar Trichomes of Evergreen Oaks (Quercus) in China and Its Implication in Taxonomy

Most of the evergreen oaks (Quercus L.) are endemic to China and distributed in a large moutainous area of southwestern China at an altitude of 2600-4000m. The delimitation of sections and species in the group has not been satisfactorily solved. The foliar trichomes are very an important character in identifying species of oaks. As a result of observation on 17 species and 2 varieties of evergreen oaks in China under scanning electron microscope, ten types of foliar trichomes are recognized: Simpleuniseriate, Simple-branched, Bulbous, Rosulate, Solitary, Stipitate-fasciculate, Fasciculate, Multiradiate, Stellate and Fused-stellate. The first four types fall into glandular trichomes and the last six non-glandular trichomes. The taxa examined have a combination of various types of the trichomes. All the evergreen oaks have non-glandular trichomes on their foliar epidermis, but glandular trichomes occur solely in certain taxa. These two types of foliar trichomes are obviously different in structure and function, which represent different adular trichomes and the last six non-glandular en oaks are divided into two groups: the glandular group and the non-glandular group according to the types of foliar trichomes and it is reasonable to divide the evergreen oaks into two sections: Sect. Suber (Reichenb.) Spach and Sect. Englerianae (A. Camus) Hsu et Jen. Foliar trichomes of the evergreen oaks show a continuity in density from species predominately with glandular trichomes at a high altitude to species solely with non-glandular trichomes at a low elevation. The characters of branching of foliar trichomes, especially the number of branches, can imply to some extent the evolutionary position of a given evergreen species. Considering the types, density and branches of foliar trichomes combined the evolutionary relationships among the evergreen oaks in China are proposed. Q. gilliana is the startpoint, from where evolution took place in two directions: glandular and non-glandular. In the glandular direction envolved are Q. aquifolioides, Q. longispica and Q. guyavaefolia. Q. pannosa is a species with the most types and highest number of glandular trichomes. In non-glandular line aligned are Q. spinosa, Q. senescens, Q. senescens var. muliensis, Q. monimotricha with the reduction of glandular trichomes and increase of non-glandular trichomes. After Q. tungmaiensis no glandular trichomes appear and it solely depends on non-glandular trichomes to protect itself. Q. granchetii is the climax in the non-glandular line with the highest density and number of branches of foliar trichomes. And then some species, such as Q. engleriana, Q. phillyraeoides, have few or no trichomes. Q. dolicholepis, Q. baronii and Q. baronii var. capitata show the close re-lationships because they share fused-stellate trichomes.     

Suitability of native and ornamental oak species in California for Agrilus auroguttatus

Goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is a new invasive species in southern California, USA. The extent of the host range of this insect is not known, but this knowledge will have a major impact on assessment of the risks that this pest poses to oaks [Quercus spp. (Fagaceae)]. We conducted laboratory tests to determine the potential suitability of native and ornamental oak species for larvae and adults of A. auroguttatus. We infested 179 cut logs (from 163 different trees) with eggs or larvae, measured neonate survival and, after 5 months, counted feeding galleries, and noted the proportion of galleries with late instars. Initial larval survival was generally high when larvae penetrated the phloem (range: 62–98% among oak species), and low by the time larvae began to feed at the phloem/xylem interface (range: 0–25% among oak species). The majority of larvae that established a visible feeding gallery survived to the fourth instar (total of 73% for all oak species). Larval galleries were established with greater frequency in red oaks (Section Lobatae) compared with other oaks (19 vs. 7 or 4%). All red oaks tested (Q. agrifolia Née, Q. kelloggii Newberry, and Q. wislizeni A. DC.) were likely suitable hosts for larvae. Larvae were apparently able to feed on some of the other oaks (Q. chrysolepis Leibmann, Q. suber L., Q. lobata Née, and Q. douglasii Hook & Arn), although it remains unclear whether these species would be preferred hosts under natural conditions. Adult longevity and fecundity varied little by species of oak foliage fed to adults. The host range of A. auroguttatus is likely limited by suitability of oak species for the larval rather than the adult life stage. Results support published field observations that red oaks are more suitable hosts than white oaks.     

Fossil oak galls preserve ancient multitrophic interactions

Trace fossils of insect feeding have contributed substantially to our understanding of the evolution of insect-plant interactions. The most complex phenotypes of herbivory are galls, whose diagnostic morphologies often allow the identification of the gall inducer. Although fossil insect-induced galls over 300Myr old are known, most are two-dimensional impressions lacking adequate morphological detail either for the precise identification of the causer or for detection of the communities of specialist parasitoids and inquilines inhabiting modern plant galls. Here, we describe the first evidence for such multitrophic associations in Pleistocene fossil galls from the Eemian interglacial (130000-115000 years ago) of The Netherlands. The exceptionally well-preserved fossils can be attributed to extant species of Andricus gallwasps (Hymenoptera: Cynipidae) galling oaks (Quercus), and provide the first fossil evidence of gall attack by herbivorous inquiline gallwasps. Furthermore, phylogenetic placement of one fossil in a lineage showing obligate host plant alternation implies the presence of a second oak species, Quercus cerris, currently unknown from Eemian fossils in northwestern Europe. This contrasts with the southern European native range of Q. cerris in the current interglacial and suggests that gallwasp invasions following human planting of Q. cerris in northern Europe may represent a return to preglacial distribution limits.     

Relation of ramet size to acorn production in five oak species of xeric upland habitats in south-central Florida

This study examined variation in two components of acorn production. Percentage of bearing ramets (stems) and number of acorns per bearing ramet were examined in five clonal oaks in three xeric habitats of south-central peninsular Florida in relation to ramet size within and between species and vegetative associations. Counts of acorns on two white oaks (Quercus chapmanii and Q. geminata) and three red oaks (Q. inopina, Q. laevis, and Q. myrtifolia) were conducted annually from 1969 to 1996 (except in 1991) on permanent grids in southern ridge sandhill, sand pine scrub, and scrubby flatwoods associations at the Archbold Biological Station, Florida, USA. Percentage of bearing individuals and mean number of acorns per bearing individual increased with increasing ramet size for all species across all vegetation associations. However, in Q. geminata and Q. myrtifolia, acorn production declined in the largest size class (>3.2 m), implying that larger individuals of these clonal species may become senescent. All oak species in sand pine scrub, which had a nearly closed overstory, had lower frequencies of bearing oaks and mean numbers of acorns compared with similar-sized individuals of the same species in the more open-canopied southern ridge sandhill and scrubby flatwoods associations, suggesting light limitation. The annual production of acorns by a given oak species was correlated across vegetative associations and annual acorn production of oak species was correlated for species within the same section. Intermediate-size class oaks contributed the most acorns per unit area, suggesting that stands managed with short fire-return times will provide fewer acorns to wildlife than stands managed to produce more variable distributions of oak size classes. However, our study suggests that long-unburned stands, such as those studied here, will maintain relatively constant levels of acorn production as a consequence of ramet replacement within the clones of these shrubby oaks to create a variable distribution of size classes. Of the oak species studied, Q. myrtifolia had the highest acorn production and the smallest acorns, while Q. laevis had the lowest acorn production and the largest acorns, suggesting an allocation trade-off between acorn numbers and size.     

Colonization, survival, and causes of mortality of Camerariu hamadryadella (Lepidoptera: Gracillariidae) on four species of host plants

Abstract.

• 1 The abundance, survival, and causes of mortality of Cameraria hamadryadella (Clemens) (Lepidoptera: Gracillariidae) were examined on four host plant species in Virginia, U.S.A. Quercus alba L. and Q.rubra L. are native within the geographic range of C.hamadryadella, and Q.robur L. and Q.benderi Baenitz are exotic. Q.robur is native to Europe, North Africa, and Asia and was probably introduced prior to 1850, and Q.benderi is of hybrid origin and introduced to cultivation before 1900. Q.alba and Q.robur are in the subgenus Lepidobalanus (white oaks), and Q.rubra and Q.benderi are in the subgenus Erythrobalanus (red oaks).
• 2 Larval mines of C. hamadryadella were abundant on both white oak species, including the exotic Q.robur, but were rare on host plants in the red oak subgenus. Un-hatched eggs of C.hamadryadella were not observed on red oaks. Other observations on host distribution indicate that C.hamadryadella is rarely found on red oaks. These observations are interpreted as circumstantial evidence that C. hamadryadella generally avoids ovipositing on red oaks.
• 3 Survival of C.hamadryadella to the adult stage was similar among all host species, but larvae tended to survive longer on hosts in the red oak subgenus. The observation of higher survival rates of early instar larvae on red oaks suggests that no nutritional or secondary chemical barrier reinforces the observed pattern of oviposition.
• 4 Significant differences in the distribution of the causes of mortality were detected between native and exotic host plant species. Larvae and pupae on native hosts were more likely to die because of predation, while those on exotic host plants were more likely to die because of parasitism and host feeding by adult female parasitoids. This pattern could arise because parasitoids prefer to forage on exotic host plants or because predators avoid foraging on exotic plants.
• 5 This study shows for C. hamadryadella that the only barriers to colonization and use of exotic hosts, in the white and red oak subgenera, are the presence of cues sufficient to stimulate oviposition and/or the absence of cues to deter oviposition. It also suggests that the presence of closely related native host plants in the region of introduction will increase the probability that exotic plants will be colonized by phytophagous insects.

     

Native oak chloroplasts reveal an ancient divide across Europe

Glacial refugia and postglacial migration are major factors responsible for the present patterns of genetic variation we see in natural populations. Traditionally postglacial history has been inferred from fossil data, but new molecular techniques permit historical information to be gleaned from present populations. The chloroplast tRNA^Leu1 intron contains regions which have been highly conserved over a billion years of chloroplast evolution. Surprisingly, in one of these regions which has remained invariant for all photosynthetic organisms so far studied, we have found intraspecific site polymorphism. This polymorphism occurs in two European oaks, Quercus robur and Q. petraea , indicating hybridisation and introgression between them. Two distinct chloroplast types occur and are distributed geographically as eastern and western forms suggesting that these oaks are each derived from at least two separate glacial refugia.     

Anatomical and developmental study of petrified Quercus (Fagaceae) fruits from the Middle Miocene, Yakima Canyon, Washington, USA

The first reported petrified acorns to show internal anatomical structure are here described from Middle Miocene (～15.6 million years old) chert of the Columbia River Basalt Group in Yakima Canyon, Washington. Quercus hiholensis Borgardt et Pigg sp. nov. is described from anatomical and morphological fruit features, as well as a little recognized anatomical feature, the umbilical complex. Acorns, each comprising a nut and its cupule, are up to 15.3 mm long and 18.8 mm wide with helically arranged, imbricate, tuberculate cupule scales. They show basal aborted ovules, short styles, broad stigmas, and lack grooves in their cotyledons. These characters and the developmental pattern seen in these fossil acorns demonstrate that Q. hiholensis conforms to genus Quercus (Fagaceae), subgenus Quercus, section Quercus (the white oaks). The correspondence of Q. hiholensis to the modern section Quercus reveals that the derived floral and fruit characters that distinguish section Quercus within the genus had evolved by the Middle Miocene.     

Post-fire recovery of acorn production by four oak species in southern ridge sandhill association in south-central Florida

We examined post-fire recovery of two components of acorn production (percentage of bearing ramets [stems] and number of acorns per bearing ramet) for four species of oaks in southern ridge sandhill vegetation in south-central peninsular Florida. Annual counts of acorns on two white oaks (Quercus chapmanii and Q. geminata) and two red oaks (Q. laevis and Q. myrtifolia) were conducted annually (except in 1991) on two 2.7-ha grids from 1969 to 1998. A prescribed burn was conducted on one of the grids in May 1993. Newly sprouted ramets of both white oaks produced acorns during the first year following the fire, whereas red oaks required 3 yr (Q. myrtifolia) or 4 yr (Q. laevis) to produce acorns. The difference in the timing of post-fire acorn production between the white and red oak species reflected the difference in the number of years from flower bud initiation to mature acorns in the two groups, with the additional year-long lag in Q. laevis probably attributable to the fact that it is typically a tree rather than a shrub species. The data suggested that percentage of bearing ramets in the smallest size class of the two white oak species was markedly lower in the burned than unburned grid in the first year of post-fire acorn production and higher in the fifth year, but these trends were not evident for the red oaks. Among all four species, differences between mean number of acorns in burned and unburned grids were significant in only two cases (the largest size class of both white oak species in the fifth year). There was no evidence of recruitment from acorns on the burned grid, possibly due to the rapid redevelopment of the shrub layer because of low mortality of the extensive clonal root systems. Rapid post-fire recovery of acorn production in xeric fire-prone habitats is presumably the result of selection to increase the probability of recovery and persistence following sufficiently intense fires that result in high oak mortality. The timing and magnitude of post-fire acorn production in sandhill and other xeric Florida associations has a potential impact on a wide variety of insects, birds, and mammals that feed on acorns, as well as on the species with which they interact.     

Spatial dynamics in the absence of dispersal: acorn production by oaks in central coastal California

We examined spatial patterns and spatial autocorrelation (synchrony) of annual acorn production in three species of oaks (genus Quercus ) over A 288 km transect in central coastal California. Over small (within-site) distances of <4 km, synchrony of acorn production between individual trees wits significant but varied through time and. for coast live oaks Q. agrifolia. differed al two sites 135 km apart. On a larger geographic scale, valley Q. lobata and blue Q. douglasii oaks exhibited significant synchrony in most distance categories between trees and sites up to 135 km apart and. in the case of coast live oaks, up to the maximum extent of the transect. Spatial patterns over this geographic scale also differed among species, with valley and blue oaks, but not coast live oaks, exhibiting distinct declines in synchrony of acorn production with distance. Interspecific synchrony in acorn production was generally lower than that within species but still significant over the entire extent of the survey. Spatial synchrony between sites was to some extent related to the same environmental variables previously found to correlate with annual acorn production within a site, suggesting that the environmental factors determining acorn production locally also influence spatial patterns over larger geographic areas. These results demonstrate that mast-fruiting in oaks occurs not only on a widespread geographic scale but also across species. They also confirm that synchrony over large geographic areas and complex spatial patterns varying in time can occur in systems where dispersal does not occur and thus environmental variability (the Moran effect) alone is likely to be driving spatial dynamics.     

A novel set of single-copy nuclear gene markers in white oak and implications for species delimitation

Oaks have often been the focus of research on plant evolution owing to their propensity to intercross and their important role in ecology and economy. Compared with traditional molecular markers, such as amplified fragment length polymorphisms (AFLPs) and simple sequence repeats (SSRs), multiple single-copy nuclear genes (SCNGs) are of greater utility in inferring evolutionary processes in oaks. Nineteen primer pairs were developed from expressed sequence tags (ESTs) of Quercus mongolica and Q. robur that could produce orthologous products in Chinese white oaks (section Quercus). These SCNG markers showed a moderate to high level of nucleotide polymorphism in 42 individuals of two closely related white oaks, Q. mongolica and Q. liaotungensis, and demonstrated high transferability across seven white oaks, four oaks from section Cerris, and one oak from section Lobatae. A phylogenetic tree based on these SCNGs provided resolution at deep nodes and robust support for delimiting populations of Q. mongolica and Q. liaotungensis; Bayesian analysis clustered individuals into their respective species with high probability and no admixture. When the same individuals were used, Bayesian clusters based on either 194 AFLPs or 19 SSRs gave comparable results, but one or several individuals respectively were identified as having admixed ancestry. This indicates that the hybridization rate between these two oaks may have been overestimated using SSR markers due to the occurrence of homoplasy. The SCNGs are powerful for species delimitation of white oaks, and these markers could be useful for future phylogenetics and phylogeography research in white oaks.     

Parasitoid complexes of lepidopteran leaf miners on oaks (Quercus dentata andQuercus mongolica) in Hokkaido,Japan

Parasitoid complexes of four microlepidopteran leaf-mining genera,Phyllonorycter, Caloptilia (Gracillariidae),Tischeria (Tischeriidae) andStigmella (Nepticulidae), which make mines on two oaks,Quercus dentata andQuercus mongolica, were studied at the Ishikari Coast, Hokkaido, northern Japan. In total, twenty-five parasitoid species were recognized.Phyllonorycter showed the highest parasitoid-species richness among the four leaf-mining genera. The number of parasitoid species associated with leaf miners onQ. dentata was nearly equal to that associated with miners onQ. mongolica, but a considerable difference was observed in the faunal make-up of parasitoids between leaf miners on the two oaks. The dominant parasitoid species differed betweenPhyllonorycter leucocorona andPhyllonorycter similis even on the same oak,Q. dentata. Factors influencing the host ranges of parasitoids and the parasitoid richness of host species or genera are discussed on the basis of the koinoparasitism/idioparasitism categorization.     

Leaf morphological analyses in four European oak species (Quercus) and their hybrids: A comparison of traditional and geometric morphometric methods

Abstract

In this study, leaf morphology was assessed in a mixed oak stand (western France) using two geometric morphometric (landmark and outline) datasets and one dataset of 19 leaf measures. Adult oaks (817 oaks), comprising four white oak species (Quercus petraea, Q. robur, Q. pubescens and Q. pyrenaica), were sampled for DNA extraction and genetic analysis (nuclear microsatellites). Leaf morphology was assessed on 336 oaks, comprising pure species and hybrids as determined by genetic assignment. This comparative study of oak leaf morphology, based on the use of two free size geometric morphometric methods and a set of leaf measurements, combined with the genetic assignment of individuals to pure species or hybrids, provided information about the differences among species and the intermediate leaf morphology of their hybrids.     

Restoration of Florida scrub vegetation in an old field through 23 years after planting

Florida scrub, a fire‐maintained, xeromorphic shrubland, hosts many rare and declining species, but most scrub habitat has been lost to development and agriculture. Formerly cultivated sites offer an opportunity to restore Florida scrub. In this 23‐year study, we test whether scrub species could be restored to an old field and whether scrub vegetation composition and structure could be reestablished over time. Scrub oaks were planted in a section of an old field in 1992 after the site was cleared and treated with herbicide. Additional oaks and other scrub species were planted in 1993. We determined survival and growth annually of a marked sample of scrub species. We sampled vegetation cover in two height strata annually on 10 permanent line‐intercept transects in the old grove and on 20 transects in adjacent, intact scrub. Initial survival of Quercus geminata exceeded that of Q. chapmanii or Q. myrtifolia. Cover of scrub oaks greater than 0.5 m increased from 1.3% in 1992 to 65.2% in 2010. However, the vegetation structure of large Q. geminata did not resemble that of native scrub. Adaptive management led to cutting large oaks in the fall of 2010, and burning the site in early 2011. Cutting and burning appeared to stimulate sprouting and clonal spread of scrub oaks. Ordination analysis indicated directional change related to increasing scrub oak cover and time since planting but the old field still differed from intact scrub. Vegetation has developed toward scrub composition and structure but exotic grasses persist.     

Taxonomic identity of Quercus coccifera L. in the Iberian Peninsula is maintained in spite of widespread hybridisation, as revealed by morphological, ISSR and ITS sequence data

Interspecific introgression is a well-known phenomenon in oaks whose ecological and evolutionary consequences, although relevant, are still unclear. We investigated molecular variation and any evidence for hybridisation in nine natural populations of kermes oak (Quercus coccifera L.) from the Iberian Peninsula. Additive patterns in 59 nrDNA ITS sequences revealed that hybrid individuals showing intermediate genotypes between kermes and holm (Q. ilex L.) oaks are very frequent, although intermediate morphotypes are uncommon. Bayesian analysis of ISSR fingerprinting patterns indicated extensive gene-flow among Q. coccifera populations and neighbouring Quercus taxa. Introgression appeared to be an active mechanism in the pair Q. coccifera–Q. ilex, but no conclusive evidence supporting hybridisation between Q. coccifera and other co-occurring Quercus species was found. The role of canalisation in the maintenance of stable morphological characters in the face of extensive introgression is discussed.     

POLLEN MORPHOLOGY AND PLANT TAXONOMY OF WHITE OAKS IN EASTERN NORTH AMERICA

An evaluation of possible approaches to fossil oak pollen identification utilized scanning electron microscopy to examine exine-surface features of 171 collections, representing 16 Quercus subgenus Lepidobalanus species and varieties of eastern North America. Twenty qualitative pollen morphological characters were defined and tabulated for each of 217 pollen grains. The data were subjected to cluster analysis and cluster diagrams were compared with published white oak taxonomy. Pollen morphology and plant taxonomy compared well in series of the subgenus Lepidobalanus due primarily to consistency of character presence and absence within species and varieties. Pollen morphology of white oaks appears to reflect plant systematics above the species level. Use of routine SEM analysis to identify series of white oaks among fossil pollen grains likely will yield valid results.     

Allozyme characterisation of four Mediterranean evergreen oak species

Polymorphism at 11 enzyme loci was used to compare the four evergreen oak species of the Mediterranean Basin and to establish their taxonomical relationships. As a comparison, two evergreen oak species from Tibet, located in the primary distribution area of evergreen oaks, were analysed at the same loci. Cladistic analyses led to the separation of a cluster of four species, namely the three Mediterranean Q. ilex, Q. coccifera and Q. alnifolia and the Tibetan Q. aquifolioides. The other Tibetan species, Q. semicarpifolia, and Q. suber, from the Western Mediterranean Basin, were very distinct genetically from the four other species. These results were not consistent with previous taxonomical treatment, based on morphology alone, which classified Q. ilex and Q. coccifera in “ilex group” (=subgenus Sclerophyllodrys O. Schwartz), and the other four species in “cerris group” (subgenus Cerris, according to Schwartz). Allozyme variation has thus provided useful information to clarify the taxonomy of evergreen oaks.     

Hollow oaks and beetle conservation: the significance of the surroundings

In this study we investigated hollow oaks (Quercus robur, Q. petrea) situated in open landscapes and in forests in Norway in northern Europe, and compared their importance for rare and threatened beetles (Coleoptera). Old, hollow oak trees, both in parks and in forests, were extremely rich in red-listed beetles, and hosted a high proportion of threatened species. The proportion of oak associated species and the mean number of red-listed beetle species per tree was similar in the two site types, but rarefaction showed that for a certain number of individuals, oaks in forests had more threatened and near-threatened species than oaks in parks. The species composition also differed between site types: Park oaks had a higher proportion of species associated with hollows and animal nests, whereas in forests, there was a higher proportion of species depending on dead oak wood in general. Four factors were significant in explaining the richness of red-listed beetles in our study: Tree circumference, cavity decay stage, proportion of oak in the surroundings, and coarse woody debris (CWD) in the surroundings. Forest oaks were smaller, but they still trapped a species richness comparable to that of the larger park oaks—probably a result of high amounts of CWD in the surroundings. We show that oaks in open landscapes and oaks in forest have only partly overlapping beetle assemblages and, thus, cannot be substituted in conservation. Planning for conservation of red-listed beetles associated with this key habitat demands a large scale perspective, both in space and time, as the surroundings have important effects on associated threatened and near threatened species.     

Fossils of the Fagaceae and their implications in systematics and biogeography

The fossil history of the Fagaceae from China and its systematic and biogeographic implications are discussed based on revisionary studies of the fossil records. No creditable macrofossil record of the Fagaceae exists in the Cretaceous deposits and all the Cretaceous microfossil reports remain equivocal and require further study. The Paleocene fossils show the appearance and diversification of the two groups corresponding to the subfamilies Fagoideae and Castaneoideae sensu Nixon. By the Eocene, all modern genera had been present. The oldest fagaceous fossils represent subfamily Fagoideae with affinities to the extant genus Trigonobalanus. The leaf fossil genus Berryophyllum, with affinities to Quercus subg. Cyclobalanopsis, has been documented by the early Eocene and might have occurred earlier than other fossils assignable to Quercus. The appearance of evergreen sclerophyllous Ouercus with entire leaves might have occurred earlier than those with toothed leaves. Deciduous, urticoid-leaved oak fossils (Quercus subg. Quercus sect. Quercus) had not appeared until the Miocene. Fossil equivalents of Trigonobalanus, Castanopsis and Lithocarpus had occurred in Europe and North America by the early Tertiary, suggesting that continuous distributions were achieved via the northern hemisphere land bridges. Three groups of evergreen sclerophyllous oaks of apparent close phylogenetic relationships occurred in the Hengduan mountains, the Mediterranean area and northwestern North America. Their fossil forms have become dominant elements of those vegetation zones since the Miocene. A shared fossil history indicates a possible biogeographic boundary formed by the ancient Mediterranean. The evidence suggests that the oaks might arrive in North America during two distinct geologic periods: evergreen sclerophyllous entire-leaved oaks appeared by the Early Tertiary, whereas thedeciduous oaks with urticoid leaves appeared in the Late Tertiary.     

壳斗科的地质历史及其系统学和植物地理学意义

在收集整理现有壳斗科化石资料的基础上,讨论了壳斗科及其各属的起源时间、地史分布和地史 演替过程以及这些化石资料在系统学和植物地理学上的意义。白垩纪尚无壳斗科可靠的大化石记录, 微化石需要进一步研究才能确定亲缘关系以及古新世壳斗科已经分化出两个类群。从以上这些事实推 论壳斗科起源于白垩纪晚期,而壳斗科现代各属出现的时间应不晚于古新世。最早发现的壳斗科化石和现代栗亚科和水青冈亚科在形态结构上非常相似,这一事实表明,壳斗科分为两个亚科的观点更接近客观事实。在水青冈亚科中,三棱栎类的化石最早出现;在栎属中,青冈亚属更接近祖先类群;在地史中全缘栎类较具齿栎类出现早,粗齿的落叶栎类出现最晚。三棱栎属、栲属和石栎属的化石在老第三纪出现于北美和欧洲的事实说明,北美、欧洲和东亚在老第三纪时有一个相通的壳斗科植物区系。南美的三棱栎是通过北美进入南美的。中国横断山、欧洲地中海沿岸和北美西北部有一类形态特征相似、亲缘关系相近的硬叶栎类,它们之间有相同的地质演替历史,它们现代分布边界可能就是古地中海的边界。美洲的栎类有两个来源,常绿硬叶栎类是通过古地中海沿岸而经北美-欧洲陆桥到达的,落叶栎类则是在中新世以后通过白令海峡到达的。