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Comparative morphological studies of fossil and living plane trees (Platanaceae) and oaks (Quercus): taxonomy, ecology, evolution
Stockholm University, Faculty of Science, Department of Botany.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Morphological characters are essential for flowering plant identification, but also provide information about diversity patterns and ecological adaptation. In woody plant species, characters of the leaf are among the most useful and can be examined on fossils as well. In this thesis, I studied leaf architecture, epidermal anatomy and reproductive structures of some fossil Platanaceae (plane trees) and an extant group of Quercus (oak) both qualitatively and quantitatively. The aim of this study was to understand past and present patterns of distribution in these taxa, their morphological variability and possible species delimitations. Platanaceae constitute today a relict taxon with a disjunct distribution, but were a taxonomically and morphologically diverse group in the geological past. The presence of the modern genus Platanus in the Late Cretaceous of Central Germany could be demonstrated through the combined analysis of leaves, flowers, fruits and pollen. The extinct genus Credneria is only represented by leaf fossils, but a unique combination of characters proved its affinity with the Platanaceae. Although several species had been described previously, a statistical analysis showed that the observed leaf polymorphism is due to environmental constraints, pointing towards a single species, Credneria denticulata. Quercus subsection Galliferae is a small group of white oaks with a disjunct distribution in the Mediterranean region, which show a high morphological variability within and low differentiation between the species. Samples from the entire distribution range were subjected to a morphological and quantitative analysis. The results demonstrated that the established species, except for Q. canariensis, are linked by clinal variation, which in turn corresponds to geographical gradients. An evaluation of epidermal characters revealed them to be of restricted use for taxon delimitation in the group. Instead, leaf and epidermal morphology provide extensive information about the ecology and biogeographic history of oaks.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University , 2011. , 53 p.
Keyword [en]
Platanaceae, Platanus, Credneria, Quercus, Galliferae, leaf architecture, epidermal anatomy, comparative morphology, character variation, variability, sample size, diversity patterns, species concepts, ecology, biogeography, evolution, plant fossils
National Category
Botany
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-62707ISBN: 978-91-7447-369-8 (print)OAI: oai:DiVA.org:su-62707DiVA: diva2:444097
Public defence
2011-10-28, Föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3. Manuscript. Paper 4. Manuscript. Available from: 2011-10-06 Created: 2011-09-27 Last updated: 2011-10-07Bibliographically approved
List of papers
1. Credneria and Platanus (Platanaceae) from the Late Cretaceous (Santonian) of Quedlinburg, Germany
Open this publication in new window or tab >>Credneria and Platanus (Platanaceae) from the Late Cretaceous (Santonian) of Quedlinburg, Germany
2008 (English)In: Review of Palaeobotany and Palynology, ISSN 0034-6667, E-ISSN 1879-0615, Vol. 152, no 04-mar, 211-236 p.Article in journal (Refereed) Published
Abstract [en]

Foliage and reproductive structures of Platanaceae from the Upper Cretaceous (Santonian) of Quedlinburg, Central Germany, were comparatively studied and their systematic affinities established. One type of foliage preserved in sandstone and rarely in clayish siltstone belongs to the extinct genus Credneria. The leaves are typically obovate with a pinnate-actinodromous venation and distinct suprabasal veins. In addition, a substantial number of leaves preserved in siltstone and rarely in sandstone are identical to modern Platanus based on leaf architecture and epidermal features. As in modern Platanus leaf margin and size were found to be of no systematic significance in both fossil leaf types. Further, staminate flower heads preserved as cleavage compressions in siltstone were found in association with Platanus leaves; they contain pollen that is identical to modern Platanus in size and type of tectum. In addition. a few three-dimensionally preserved staminate flower heads with ca. 50 flowers on a receptaculum are described. Each flower appears to have a two-whorled perianth and six or seven stamens. The organs of the outer perianth whorl show a distinct epidermal cell pattern different from the inner ones. All perianth organs have the same length as the stamens. Stamens are bithecate and contain pollen identical to that found in compression fossils. Pistillate heads preserved in siltstone consist of numerous achenes with persistent styles, which show close similarity to modern Platanus. It remains unclear, whether additional inflorescence heads of uncertain sex found in sandstone that are slightly larger than those preserved in siltstone belong to the leaves of Credneria. Association evidence links vegetative and reproductive structures preserved in siltstone and indicates the presence of the modern genus Platanus in the Santonian.

Keyword
Late Cretaceous, Quedlinburg, Platanaceae, Credneria, Platanus, leaf fossils, reproductive structures, pollen, comparative morphology
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-57699 (URN)10.1016/j.revpalbo.2008.05.004 (DOI)000261704400008 ()
Note
authorCount :3Available from: 2011-05-17 Created: 2011-05-16 Last updated: 2017-12-11Bibliographically approved
2. Credneria Zenker (Platanaceae): an extinct endemic plane tree from the Upper Cretaceous (Santonian) of Central Germany and its ancient environment
Open this publication in new window or tab >>Credneria Zenker (Platanaceae): an extinct endemic plane tree from the Upper Cretaceous (Santonian) of Central Germany and its ancient environment
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Leaves of the Late Cretaceous angiosperm Credneria from its type locality in the Subhercynian Cretaceous Basin were investigated with morphological and statistical methods. Quantitative analysis of the morphological variability of the leaves suggests that the previously distinguished morphotypes Ia and Ib constitute sun and shade leaves of a single species, Credneria denticulata. Qualitative evaluation of the leaves reveals a combination of characters that link Credneria with the Platanaceae. Most determinative for this affiliation were an actinodromous venation, the presence of several pairs of suprabasal veins at the leaf base, spinose teeth and an inflated petiole base that originally enclosed the axillary bud. More than 50 species of Credneria have been described from localities outside the Subhercynian Cretaceous Basin. Although some of these species resemble the leaves from the type locality superficially, many of the determinative characters differ in detail or are absent. Many of these fossils were later assigned to Platanus. In the context of the pronounced provincialism of many taxa during the Cretaceous, it is likely that Credneria was endemic to Central Europe. Sedimentological features of the host deposit point to an accumulation of Credneria leaves in a tidal-influenced coastal landscape close to a shallow sea with cyclic transgressions and regressions. Credneria most likely inhabited a disturbed, early successional environment in a coastal delta floodplain. The occurrence of fossil tropical soils (hematitic oxisols) points to a warm and humid climate that probably was seasonal.

Keyword
Credneria, Platanaceae, leaf morphology, morphological variability, quantitative analysis, character combination, sedimentary environment, Cretaceous plant ecology
National Category
Natural Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-62711 (URN)
Available from: 2011-09-27 Created: 2011-09-27 Last updated: 2011-09-29Bibliographically approved
3. Clinal variation over species boundaries?: A morphological analysis of the Mediterranean ‘Gall Oaks’, Quercus subsectio Galliferae (Spach) Guerke (Fagaceae)
Open this publication in new window or tab >>Clinal variation over species boundaries?: A morphological analysis of the Mediterranean ‘Gall Oaks’, Quercus subsectio Galliferae (Spach) Guerke (Fagaceae)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The distribution ranges of many so-called Tertiary relict taxa in western Eurasia are disjunct and reflect historical processes of area disruptions and shifts. In woody angiosperms (trees), such taxa have variously been treated as species or infraspecific taxa. Here, we revised a group of morphologically well-defined western Eurasian white oaks (Quercus Group Quercus) belonging to the subsection Galliferae, with a disjunct distribution in the western and eastern parts of the Mediterranean Basin. Based on previous extensive molecular studies, there is no clear pattern of genetic differentiation among members of this group. In our analysis we used 72 quantitative and qualitative morphological characters measured on more than 2000 leaves, twigs, cupules and acorns to assess the variability of the taxa and their systematic relationships. The results indicate a clear gap between the western species Q. canariensis and the remaining five taxa of the group. The latter are best accommodated within a single species Q. faginea with a disjunct distribution in the Western and Eastern Mediterranean. This disjunction appears to be young. Fossils with strong affinities to Q. canariensis and eastern Mediterranean populations of Galliferae are known from the (early) Pliocene of Italy. This may suggest that the disruption of the formerly homogeneous distribution range of Galliferae began about 5.3-3.6 million years ago and is in agreement with the very weak molecular differentiation within the subsection.

Keyword
Quercus, morphology, interspecific variability, intraspecific variability, quantitative analysis, species delimitation, taxonomy, biogeography
National Category
Natural Sciences
Research subject
Plant Morphology; Plant Ecology
Identifiers
urn:nbn:se:su:diva-62713 (URN)
Available from: 2011-09-27 Created: 2011-09-27 Last updated: 2011-09-29Bibliographically approved
4. Trichome types, foliar indumentum, and epicuticular wax in the Mediterranean ‘Gall Oaks’, Quercus subsectio Galliferae (Spach) Guerke (Fagaceae): implications for taxonomy, ecology, and evolution
Open this publication in new window or tab >>Trichome types, foliar indumentum, and epicuticular wax in the Mediterranean ‘Gall Oaks’, Quercus subsectio Galliferae (Spach) Guerke (Fagaceae): implications for taxonomy, ecology, and evolution
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Trichome characters are often considered taxonomically important in oak species. Here, we investigated a group of Mediterranean oaks, Quercus subsectio Galliferae and Q. pubescens, using a large dataset and covering the entire distribution range of the group. Due to different interpretations of terms in previous studies, trichome terminology was re-assessed aiming at a practicable nomenclature. In contrast to previous studies, we found that acicular, bifurcate, fasciculate, stellate, uniseriate and capitate trichomes are represented in all taxa. One exception is the lack of bifurcate trichomes in Quercus canariensis. This suggests that seemingly taxonomically informative presence/absence data for trichome types as reported previously may be a result of too small sample size and hence unrepresentative. In combination with other morphological characters (leaf shape, size and texture), features of the indumentum, such as the floccose, easily removable trichomes in Quercus canariensis can be important in species delimitation. Making use of trichome characteristics in Quercus subsectio Galliferae requires exhaustive sampling of all taxa in order to extract reproducible taxonomic signal from quantitative characters. This would be the prerequisite for building datasets that could be used for phylogenetic studies, investigations of character evolution and comparative morphological studies.

Keyword
Quercus, trichomes, trichome classification, foliar indumentum, epicuticular wax, taxonomy, ecological significance, evolution
National Category
Natural Sciences
Research subject
Plant Ecology; Plant Morphology; Plant Systematics
Identifiers
urn:nbn:se:su:diva-62715 (URN)
Available from: 2011-09-27 Created: 2011-09-27 Last updated: 2011-09-29Bibliographically approved

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