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Title: Evolution and adaptive radiation of Bromus L. Sect. Genea Dum. (Poaceae)
Author: Sales, Fatima
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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The 8(-9) annual species of Bromus generally placed in sect Genea were investigated taxonomically and biologically with the aim of improving their classification and giving a better understanding of their morphology and relationships. The species are widely distributed in the Mediterranean countries, SW Asia and also in northern Europe; some are important introduced weeds in other regions of the world, mainly with a Mediterranean-type climate. None has previously been investigated throughout their total areas. In this multi-disciplinary approach, material falling into the following existing taxa were studied: B.diandrus, fasciculatus, (Haussknechtii), madritensis, rigidus, rubens, sericeus, sterilis and tectorum. The investigation was based on: herbarium resources, field-work, an experimental plasticity study, geography/ecology, a computer analysis, anatomy, SEM studies, serology and cytology. For reasons of convenience, the species were considered in 3 groups. In each of these, varying degrees of emphasis were given to the results of the different investigations listed above. In the B.tectorum-sericeus group, a computer analysis, based on information from a very large number of herbarium specimens supported the recognition of one species with 2 subspecies (B.tectorum subsp. tectorum and subsp. lucidus Sales). In this group, the taxonomic and evolutionary significance of the features of dispersal biology was stressed. In the B.sterilis-diandrus-rigidus group, it is shown that the existing typification of B.sterilis is incorrect. B.diandrus and rigidus, so often recognized as independent species are here regarded as varieties of one species. In the last group (B.madritensis (haussknechtii), rubens, fasciculatus), particular attention was given to B.fasciculatus. Its uniform morphology is stressed; no infra-specific taxa are recognized within it. Leaf anatomy was studied and described; no major or significant differences were revealed in the species studied. Micromorphology was investigated for many vegetative and floral parts of the plant. These showed, inter alia, that certain characters, such as the shape of the callus scar have previously been given undue emphasis. SEM studies provided a new insight into some characters of biological importance, including stomata on the awns and the incomplete development of callus at floret base on chorispermous plants. A chapter on cytology confirms previous records of chromosome number and describes an improved technique. Serological studies of double diffusion confirmed the close relation of Genea species and supported, in general, the recognition of the three groups based on morphology. B.sterilis and B.madritensis are probably at the core of sect. Genea from which 2 evolutionary lines towards B.diandrus var. rigidus and B.fasciculatus developed. B.tectorum may represent a link between sect. Genea and the B.pectinatus complex (sect. Bromus). These aspects are discussed in the chapter on adaptive radiation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available