Quercus Group Research Articles

Generalized height-diameter models with random effects for natural forests of central Mexico

Background: Tree height is an important variable in forestry, as it is commonly used to estimate volume and biomass, and to evaluate site productivity. In this study, we developed four generalized equations to model height-diameter ( h-d) relationships for coniferous and broadleaf species. For this purpose, we used information from 49 permanent sampling plots located in the natural forests of Puebla, Mexico. Non-linear fixed and mixed-effects modeling approaches were used to fit generalized versions of the Gompertz function to Pinus patula and the Pinus group, the Näslund function to Abies religiosa, and the Curtis function to the Quercus group. Results: Stand variables included in the models were the number of trees per hectare ( N), quadratic mean diameter ( dg), and basal area per hectare ( G). The results showed a model efficiency (EF) = 0.91 and root mean square error (RMSE) = 2.04 for P. patula, as well as an EF = 0.91 and RMSE = 1.63 for the Pinus group. The EF and RMSE for Abies religiosa were 0.88 and 2.21, while for the Quercus group these values were 0.72 and 1.9, respectively. From the mixed-effects model calibration, only a sub-sample of three trees from different quantiles of the diameter distribution is required to make accurate predictions. No stand-level variables related to tree height are included in any of the selected models, thus no additional measurements beyond tree diameter are required. Conclusion: Compared to conventional non-linear least squares (ONLS), mixed-effects models are more flexible and accurate and represent a new tool for sustainable forest management of natural forests in the study area.

Remarkably conserved plastid genomes of Quercus group Cerris in China: comparative and phylogenetic analyses

Quercus is one of the most important plant genera in terms of economic and ecological values, with approximately 500 species worldwide. Quercus group Cerris is endemic to Eurasia (with 11 species), and three species (Quercus acutissima, Quercus chenii and Quercus variabilis) are widely distributed in China. Here, we sequenced the complete plastid genomes of Q. acutissima and Q. chenii by Illumina pair‐end sequencing and obtained an additional plastome of Q. variabilis from GenBank. In spite of geographically distant sampling, the three available plastomes of Cerris were remarkably conserved with regard to genome size, gene organization, GC content, and IR/SC boundary regions. A phylogenetic analysis showed that the Cerris group is nested within the Ilex group, forming a Cerris‐Ilex clade. The current study provide plastid genomic‐scale data for the less intensively studied Cerris group, which should be useful for studying speciation processes, geographical structure and phylogeny within the group in the future.

Considering neighborhood effects improves individual dbh growth models for natural mixed-species forests in Mexico

More accurate diameter at breast height (dbh)-growth models are needed for developing management tools for mixed-species forests in Mexico. Individual distance-dependent dbh growth models that quantify local neighborhood effects have been developed for four species groups in such forests. The performance of the models is improved by distinguishing between inter- and intraspecific group competitions. The management of mixed-species forests in the northwest of Durango, Mexico, is mainly based on the selection method. Understanding the interspecific and intraspecific competition is critical to developing management tools for such mixed-species forests. An individual-based distance-dependent modeling approach was used to model the growth of dbh and to evaluate neighborhood effects for four species groups in Mexican mixed-species stands. Twenty-two species were classified into four groups: Pinus (seven species), other conifers (three species), other broadleaves (four species), and Quercus (eight species). Four methods were used to select neighboring trees and 12 competition indices (CIs) were calculated. Comparisons of the neighboring trees selection methods and CIs and tests of assumptions about neighborhood effects were conducted. Intra-species-group competition significantly reduced diameter growth for all species groups, except for the Quercus group. The Pinus, other conifers, and Quercus groups had significant and negative neighborhood effects on the other broadleaves species group, and not vice versa. The Quercus group also had negative neighborhood effect on the Pinus and other conifers species groups, and not vice versa. The Pinus and other conifers species groups had negative neighborhood effects on each other. All fitted age-independent dbh growth models showed a good of fit to the data (adjusted coefficient of determination larger than 0.977). The growth models can be used to predict dbh growth for species groups and competition in mixed-species stand from Durango, Mexico.

Taxonomy and palaeoecology of two widespread western Eurasian Neogene sclerophyllous oak species: Quercus drymeja Unger and Q. mediterranea Unger

Sclerophyllous oaks (genus Quercus) play important roles in Neogene ecosystems of south-western Eurasia. Modern analogues (‘nearest living relatives’) for these oaks have been sought among five of six infrageneric lineages of Quercus, distributed across the entire Northern Hemisphere. A revision of leaf fossils from lower Miocene to Pliocene deposits suggests that morphotypes of the Quercus drymeja complex are very similar to a number of extant Himalayan, East Asian, and Southeast Asian species of Quercus Group Ilex and may indicate subtropical, relatively humid conditions. Quercus mediterranea comprises leaf morphotypes that are encountered in modern Mediterranean species of Quercus Group Ilex, but also in Himalayan and East Asian members of this group indicating fully humid or summer-wet conditions. The fossil taxa Quercus drymeja and Q. mediterranea should be treated as morphotype complexes, which possibly comprised different biological species at different times. Quercus mediterranea, although readily recognizable as a distinct morphotype in early to late Miocene plant assemblages, may in fact represent small leaves of the same plants that constitute the Quercus drymeja complex. Based on the available evidence, the species forming the Q. drymeja complex and Q. mediterranea thrived in fully humid or summer-wet climates. The onset of the modern vegetational context of Mediterranean sclerophyllous oaks is difficult to trace, but may have been during the latest Pliocene/early Pleistocene.

Phylogeographic structuring of plastome diversity in Mediterranean oaks (Quercus Group Ilex, Fagaceae)

Oaks of Quercus Group Ilex are emblematic components of the Mediterranean landscapes and the full extent of their diversity in a geographic context is still poorly assessed. In order to detail differentiation patterns within Group Ilex and to illuminate causes and circumstances that underlie the distribution of its lineages, we examined plastome differentiation in the four species currently representing this oak group across the Mediterranean Basin (Quercus ilex, Quercus coccifera, Quercus aucheri, Quercus alnifolia). Plastid DNA variation was explored with three markers on 124 individuals and spatial analyses were performed with phylogenetic and landscape genetics approaches. A strong geographic sorting, entirely decoupled from species boundaries, was found. Spatial coincidences with phylogenetic splits highlights the presence of four geographic regions (the Middle East, the Aegean region, the central and the western Mediterranean) characterised by different degrees of isolation. Distinct sub-regional structures were identified. Inter- and intra-lineage divergence patterns appear to reflect the complex orogeny of the Mediterranean region and Pleistocene climatic oscillations, while a few widespread haplotypes might represent the remnants of the ancestral Group Ilex range. Regional differentiation in this group is recognised to be triggered by a number of factors, including disruption of the original range, incomplete lineage sorting, repeated phases of asymmetrical introgression and isolation. The key role played by some Mediterranean regions on the range establishment and dynamics of this oak group is discussed.

Leaf epidermal features of Quercus Group Ilex (Fagaceae) and their application to species identification

Leaf epidermal features are useful for elucidating the taxonomy and systematics of oak species. Quercus Group Ilex has a wide distribution mainly in subtropical areas of Eurasia with rich fossil records since the Oligocene, but no comprehensive study has ever been conducted on its diversity of leaf epidermal features. We compared the leaf epidermal features of 37 species of Quercus Group Ilex and Q. suber from Group Cerris using light microscopy (LM) and scanning electron microscopy (SEM). A total of five trichome types (including three glandular and two non-glandular types) and two trichome base types were found. Leaf epidermal features of Group Ilex show typical xeromorphic features. The stomatal complexes are stephanocytic. The leaf trichome types and trichome base types are stable at inter- and intra-species levels. The trichomes, stomatal sizes and density and the ray arm lengths show a wide variation during developing stages within species. The leaf epidermal features show a highly convergent pattern in the genus Quercus based on tree-mapping analysis, except for the multiple epidermal layers on the adaxial surface supports the monophyletic origin of section Heterobalanus. Cluster analysis of leaf epidermal characters infers two morphological subgroups within Group Ilex: (1) the capitate and (2) the branched uniseriate. The trichomes and trichome base types, and their density are useful for species identification, which can improve the accuracy of assigning fossil leaves to their nearest living relatives in Group Ilex.

Pollen morphology and ultrastructure of Quercus with focus on Group Ilex (=Quercus subgenus Heterobalanus (Oerst.) Menitsky): implications for oak systematics and evolution

It has been suggested that pollen ornamentation can be used to distinguish infrageneric groups in Quercus. Here, we document pollen morphology of nearly all species of Quercus Group Ilex and show that they share distinctive microrugulate pollen ornamentation. Furthermore, pollen ultrastructure of all six infrageneric groups of Quercus was studied comparatively and evaluated using a phylogenetic framework for Fagaceae. Characteristics of the foot layer, such as its thickness and continuity, and the ratio foot layer to tectum are not stable within infrageneric groups of Quercus. The foot layer in derived groups (Groups Cerris, Quercus, Lobatae) is irregular, discontinuous and thin (type 2 foot layer). Members of Groups Cyclobalanopsis and Ilex either have a regular, continuous, and comparatively thick foot layer (type 1), or a type 2 foot layer. Only Group Protobalanus consistently has a type 1 foot layer and is similar to Trigonobalanus and Colombobalanus among trigonobalanoids, and to castanoids. Because (I) all except for one species of Castanea and Nothofagus have a type 1 foot layer and (II) basal groups in Quercus may have a type 1 foot layer, we suggest that this is the ancestral state in Fagaceae, and that the type 2 foot layer of Fagus is derived.

Fagaceae pollen from the early Cenozoic of West Greenland: revisiting Engler's and Chaney's Arcto-Tertiary hypotheses.

In this paper we document Fagaceae pollen from the Eocene of western Greenland. The pollen record suggests a remarkable diversity of the family in the early Cenozoic of Greenland. Extinct Fagaceae pollen types include Eotrigonobalanus, which extends at least back to the Paleocene, and two ancestral pollen types with affinities to the Eurasian Quercus Group Ilex and the western North American Quercus Group Protobalanus. In addition, modern lineages of Fagaceae are unambiguously represented by pollen of Fagus, Quercus Group Lobatae/Quercus, and three Castaneoideae pollen types. These findings corroborate earlier findings from Axel Heiberg Island that Fagaceae were a dominant element at high latitudes during the early Cenozoic. Comparison with coeval or older mid-latitude records of modern lineages of Fagaceae shows that modern lineages found in western Greenland and Axel Heiberg likely originated at lower latitudes. Further examples comprise (possibly) Acer, Aesculus, Alnus, Ulmus, and others. Thus, before fossils belonging to modern northern temperate lineages will have been recovered from older (early Eocene, Paleocene) strata from high latitudes, Engler’s hypothesis of an Arctic origin of the modern temperate woody flora of Eurasia, termed ‘Arcto-Tertiary Element’, and later modification by R. W. Chaney and H. D. Mai (‘Arcto-Tertiary Geoflora’) needs to be modified.

Evolutionary trends and ecological differentiation in early Cenozoic Fagaceae of western North America.

• The early Cenozoic was a key period of evolutionary radiation in Fagaceae. The common notion is that species thriving in the modern summer-dry climate of California originated in climates with ample summer rain during the Paleogene.• We investigated in situ and dispersed pollen of Fagaceae from the uppermost Eocene Florissant fossil beds, Colorado, United States, using a combined light and scanning electron microscopy approach.• Pollen types of Castaneoideae with affinities to modern Castanea, Lithocarpus, and Castanopsis were recognized. Pollen of the extinct genus Fagopsis represents a derived type of Castaneoideae pollen. Infrageneric groups of Quercus were well represented, including pollen of Group Protobalanus. The taxonomic diversity of Fagaceae and of the total plant assemblage indicates a mosaic of microclimates, that range from pronounced to weakly seasonal climates and depend on slope aspect and elevation. Continental climatic conditions may have triggered the evolution of sclerophyllous leaves and adaptive radiation in Quercus and other taxa thriving today under distinctly summer-dry and winter-dry climates.• Vegetation types similar to modern vegetation belts of the Coastal Ranges (chaparral, nemoral conifer forest) were established in the Front Range in the late Eocene. Coeval plant assemblages from the Coastal Ranges of California indicate distinctly subtropical, moist climates. Hence, characteristic elements found today in the summer-dry and winter-dry climates of Pacific North America (Quercus Group Protobalanus, Notholithocarpus) may opportunistically have dispersed into their modern ranges later in the Cenozoic. This scenario is in contrast to the evolution and migration patterns of their western Eurasian Mediterranean counterparts (Quercus Group Ilex).

Fagaceae from the early Oligocene of Central Europe: Persisting new world and emerging old world biogeographic links

Dispersed pollen from phosphoritic nodules of early Oligocene age from Cospuden (Rupelian, Saxony, Central Europe) comprises six distinct types of Fagaceae belonging to four to five genera, three of which belong to extinct lineages. Eotrigonobalanus and Trigonobalanopsis have stratigraphic ranges from the Eocene to the Miocene and the Pliocene, respectively, and an unassigned fagaceous pollen type might belong to a lineage related to the middle to late Oligocene Amentoplexipollenites from North America. Also pollen of Eotrigonobalanus from Cospuden is strikingly similar to pollen attached to staminate catkins in middle to late Oligocene sediments from the North American Gulf Coastal Plain. Both types of pollen co-occur with foliage of the Eotrigonobalanus type ( Dryophyllum, Berryophyllum). Furthermore, cupules and fruits from the middle Eocene to lower Miocene in Europe ( Trigonobalanus andreanszkyi Mai) and the Oligocene of the Gulf Coastal Plain are structurally similar. This suggests an intercontinental distribution of this extinct lineage of Fagaceae with migration across the North Atlantic. Trigonobalanopsis is endemic during the Cenozoic in Europe. Although present in late Miocene sediments of Iceland it has not been reported from North America. The extant genera Fagus and Quercus are not known prior to the Eocene. The unequivocal presence of Fagus in Rupelian sediments of Central Europe is the oldest record of the genus in western Eurasia. Fagus migrated to Europe from the east (Central and East Asia) after the closure of the Turgai Seaway. Pollen belonging to Quercus Group Ilex also marks the oldest record for Europe. Today, this group of oaks is endemic to Eurasia with isolated occurrences in the Mediterranean, the Himalayas, and East Asia. It is unclear, whether the group originated in Europe or East Asia. Pollen belonging to either Quercus Group Quercus or Group Lobatae (white and red oaks) dates back at least to the Eocene in Europe (Baltic Amber). Based on systematic affinities of leaves from late Oligocene sediments in Saxony, pollen from Cospuden with the distinctive features of these infrageneric groups may represent Group Lobatae (red oaks). This group is at present confined to North America, but appears to be represented in the fossil record of East Asia and Europe.

The oaks of western Eurasia: Traditional classifications and evidence from two nuclear markers

AbstractPhylogenetic relationships among species of Quercus (oaks) from western Eurasia including the western part of the Himalayas are examined for the first time. Based on ITS and 5S–IGS data three major infrageneric groups are recognized for western Eurasia: the cerroid, iliciod, and roburoid oaks. While individuals of the cerroid and ilicoid groups cluster according to their species, particularly in the 5S–IGS analyses, individuals of species of roburoid oaks do not cluster with exception of Quercus pontica. The Cypriot endemic Quercus alnifolia belongs to the ilicoid oaks, in contrast to traditional views placing it within the cerroid oaks. Based on all ITS data available, the groups identified for western Eurasia can be integrated into a global infrageneric framework for Quercus. The Ilex group is resurrected as a well–defined group that comprises taxa traditionally placed into six subsections of Q. sects. Cerris and Lepidobalanus (white oaks) sensu Camus. Phylogenetic reconstructions suggest two major lineages within Quercus, each consisting of three infrageneric groups. Within the first lineage, the Quercus group (roburoid oaks in western Eurasia) and the Lobatae group evolved by “budding” as is reflected by incomplete lineage sorting, high variability within groups, and low differentiation among groups. The groups of the second lineage, including the Cyclobalanopsis, Cerris (cerroid oaks in western Eurasia), and Ilex (ilicoid oaks in western Eurasia) groups, evolved in a more tree–like fashion.

Utility of ITS sequence data for phylogenetic reconstruction of Italian Quercus spp.

Nuclear ribosomal DNA sequences encoding the 5.8S RNA and the flanking internal transcribed spacers (ITS1 and ITS2) were used to test the phylogenetic relationships within 12 Italian Quercus taxa (Fagaceae). Hypotheses of sequence orthology are tested by detailed inspection of some basic features of oak ITS sequences (i.e., general patterns of conserved domains, thermodynamic stability and predicted conformation of the secondary structure of transcripts) that also allowed more accurate sequence alignment. Analysis of ITS variation supported three monophyletic groups, corresponding to subg. Cerris, Schlerophyllodrys (= Ilex group sensu Nixon) and Quercus, as proposed by Schwarz [Feddes Rep., Sonderbeih. D, 1-200]. A derivation of the “ Cerris group” from the “ Ilex group” is suggested, with Q. cerris sister to the rest of the “ Cerris group.” Quercus pubescens was found to be sister to the rest of the “ Quercus group.” The status of hybrispecies of Q. crenata ( Q. cerris × Q. suber) and Q. morisii ( Q. ilex × Q. suber) was evaluated and discussed. Finally, the phylogenetic position of the Italian species in a broader context of the genus is presented. The utility of the ITS marker to assess the molecular systematics of oaks is therefore confirmed. The importance of Italy as a region with a high degree of diversity at the population and genetic level is discussed.

Fossil picrodendroid fruit from the Upper Danian of Nûgssuaq, West Greenland

Rosenkrantzia picrodendroides n.gen. et n.sp., based on 4. 7 specimens of fossil fruit in very good preservation, is described. The fruit was a nut (or drupe), with a thick pericarp of primitive anatomy. It is l-locular, containing one fully developed seed; about half of the specimens also contain remnants of a second aborted seed. The seed is pendulous from an apical placenta and has a long longitudinal raphe. Hilum is distal, chalaza basal. The original ovary can be reconstructed: l-locular with min. two ovules, pendulous from the distal placenta, anatropous. The fully developed seed consists mainly of two thick, interfolded cotyledons with no distinct endosperm. The taxonomical investigation includes a study of fruits of two of the recent Picrodendron species. A phylogenetic conclusion is advanced which supports the position of the Picrodendraceae in the order Juglandales. The taxonomic position of Rosenkrantzia appears to lie somewhere between the Cupuliferae ( Quercus group) and Juglandales, or in palaeontological terms, between the Dryophyllum and Dewalquea groups.