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Clinal variation over species boundaries?: A morphological analysis of the Mediterranean ‘Gall Oaks’, Quercus subsectio Galliferae (Spach) Guerke (Fagaceae)
Stockholm University, Faculty of Science, Department of Botany.
Swedish Museum of Natural History, Department of Palaeobotany.
(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 [en]
Quercus, morphology, interspecific variability, intraspecific variability, quantitative analysis, species delimitation, taxonomy, biogeography
National Category
Natural Sciences
Research subject
Plant Morphology; Plant Ecology
URN: urn:nbn:se:su:diva-62713OAI: diva2:444092
Available from: 2011-09-27 Created: 2011-09-27 Last updated: 2011-09-29Bibliographically approved
In thesis
1. Comparative morphological studies of fossil and living plane trees (Platanaceae) and oaks (Quercus): taxonomy, ecology, evolution
Open this publication in new window or tab >>Comparative morphological studies of fossil and living plane trees (Platanaceae) and oaks (Quercus): taxonomy, ecology, evolution
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.
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
Research subject
Plant Ecology
urn:nbn:se:su:diva-62707 (URN)978-91-7447-369-8 (ISBN)
Public defence
2011-10-28, Föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00 (English)
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

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Tschan, Georg Florian
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