The 8(-9) annual species of <i>Bromus</i> generally placed in sect <i>Genea</i> 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: <i>B.diandrus</i>, <i>fasciculatus</i>, (<i>Haussknechtii</i>), <i>madritensis</i>, <i>rigidus</i>, <i>rubens</i>, <i>sericeus</i>, <i>sterilis</i> and <i>tectorum</i>. 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 <i>B.tectorum-sericeus</i> group, a computer analysis, based on information from a very large number of herbarium specimens supported the recognition of one species with 2 subspecies (<i>B.tectorum</i> subsp. <i>tectorum</i> and subsp. <i>lucidus</i> Sales). In this group, the taxonomic and evolutionary significance of the features of dispersal biology was stressed. In the <i>B.sterilis</i>-<i>diandrus</i>-<i>rigidus</i> group, it is shown that the existing typification of <i>B.sterilis</i> is incorrect. <i>B.diandrus</i> and <i>rigidus</i>, so often recognized as independent species are here regarded as varieties of one species. In the last group (<i>B.madritensis</i> (<i>haussknechtii</i>), <i>rubens</i>, <i>fasciculatus</i>), particular attention was given to <i>B.fasciculatus</i>. 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 <i>Genea</i> species and supported, in general, the recognition of the three groups based on morphology. <i>B.sterilis</i> and <i>B.madritensis</i> are probably at the core of sect. <i>Genea</i> from which 2 evolutionary lines towards <i>B.diandrus</i> var. <i>rigidus</i> and <i>B.fasciculatus</i> developed. <i>B.tectorum</i> may represent a link between sect. <i>Genea</i> and the <i>B.pectinatus</i> complex (sect. <i>Bromus</i>). These aspects are discussed in the chapter on adaptive radiation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:661530 |
| Date | January 1991 |
| Creators | Sales, Fatima |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11349 |
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