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|Title:||Biosystematic studies in Cerastium tomentosum group (Caryophyllaceae).|
|Authors:||Khalaf, Mohammed Kamel.|
|Presented at:||University of Leicester|
|Abstract:||Work involving morphological, cytological, anatomical and palynological characters, reproductive biology, geographical distribution and hybridization has been carried out on C. tomentosum group and has led to its reclassification. Three of the nine species (C. tomentosum, C. decalvans and C. gibraltaricum), show a very wide morphological variability, while the remaining 6 species (C. argenteum, C. biebersteinii, C. candidissimum, C. lineare, C. moesiacum and C. grandiflorum) have much narrower morphological limits. Of the taxa investigated, C. candidissimum, C. lineare, C. argenteum and C. biebersteinii are diploid; C. grandiflorum and C. tomentosum var. minus are tetraploid; C. decalvans, C. tomentosum var. tomentosum and both varieties of C. gibraltaricum are diploid, tetraploid and hexaploid; and C. moesiacum is diploid and octoploid. B-chromosomes have been reported for the first time in C. tomentosum and C. grandiflorum. The base number is considered as 18 for the group. Vegetative anatomical investigations revealed that both varieties of C. tomentosum are completely different in cell length ratio of the non-glandular hairs from those of all other species. C. gibraltaricum differs strikingly from the remaining taxa of the group by the shape of vascular bundles of the stem. C. moesiacum can be distinguished from the other taxa of the group by the high number of layers of cells in the stem cortex and the existence of patches of fibres through the cortex. I have found that C. tomentosum group taxa are facultative outcrossers. Heterogamy is reinforced by pronounced protandry as well as by the reflexion of the stamens away from the receptive stigmas. Geitonogamy is undoubtedly responsible for a high percentage of pollinations, but genetic exchange between individuals in a population or between different populations probably is a normal occurrence. Over 2500 intra- and inter-specific crosses within C. tomentosum group and between it and 6 other species were carried out. The results show that within C. tomentosum group hybrids were relatively easily achieved, and some of them were fertile. Of the other crosses, those between tetraploid cytotypes of C. tomentosum and C. arvense were the most successful, but always sterile. Sterile F1 hybrids were also obtained between various taxa outside the group (especially involving C. alpinum and C. arvense). There is little evidence in Cerastium that higher ploidy levels are better as one sex than the other in crosses with lower ploidy levels. This study suggests exclusion of C. gibraltaricum and C. moesiacum from C. tomentosum group, leaving a far more homogeneous group whose seven members are very likely to be phylogenetically closely related. Within these, C. candidissimum and C. grandiflorum are very easily demarcated due to their branched hairs. The remaining five species (C. tomentosum, C. decalvans, C. lineare, C. biebersteinii and C. argenteum), forming the core of the group, are all totally allopatric.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Biology|
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