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Title: The experimental taxonomy of Stachys ambigua Sm., S. palustris L., and S. sylvatica L.
Author: Wilcox, Christopher Charles
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1973
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The putative hybrid, Stachys x ambigua 8m, is shown to overlap with S. palustris L. in all the morphological characters studied and in flower pigments. A discontinuity in morphological variation usually exists between S. ambigua and S, sylvatica L. in these characters. Chromosome counts /S . sylvatica 2n = (62)-66-<68), 8. p a lu stris 2n = (97)-102- (103) and S. ambigua (78)-84-(862/ 3ind m eiotic pairing relation ships have confirmed the hybrid origin of 8. ambigua. No field populations were discovered with a pattern of morphological variation indubitably attributable to introgressive hybridization between 3. ambigua and 8. palustris. A scatter diagram, based on leaf data, of a ll the populations shows an intergradation between 8. ambigua and 8. palustris previously interpreted as in trogression. Morphological in tergradation occurs because 1. S. palustris is a highly polymorphic species exhibiting a high degree of both within - and between - population variability , and 2. S. ambigua plants are not intermediate but morphologically closer to 8. palustris than S. sylvatica. The pollen fertility of 8. ambigua populations is shown to be low ( ^ 5%) but th is is unlikely to be itself an effective barrier to backcrossing. Pollinators show no discrimination between the three taxa, and rare backcrosses may exist in nature. There is, however, no evidence of the occurrence of hybrid swarms. Competition experiments between the three taxa through two seasons of growth show that eliminations of competing genotypes are density-dependent. In tersp ecific competition is not likely to be the most important factor causing the absence of one or both parents from localities where the hybrid occurs. Accidental or desired distribution of rhizome fragments of the hybrid by man and the disappearance of S. palustris from marsh land as a result of drainage are considered to be more important causal factors. Chromatographic spot patterns from flower samples of Stachvs populations were associated by computer using three different coefficients of association - simple matching, Jaccard and Dice coefficients. These were evaluated by their application to the data of Moore e t al (1970). The simple matching co efficien t used in cohjunction with the weighted variable group clu sterin g procedure is shown to be the most effective in reflecting the relationships between both the Stachvs and the Empetrum rubrum samples.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Botany