The objective of this study of hybridization between H. mantegazzianum Somm. & Lev. and H. sphondylium L. in Britain was to provide evidence for the existence of hybrids from field observations and experimental crosses. H. sphondylium is native to the British Isles; H. mantegazzianum was introduced to Europe from the Caucasus in 1895. During the nineteenth century several species of Heracleum were cultivated in Britain, but only H. mantegazzianum is now widely naturalized along rivers and on waste ground in south-east Scotland. In 1976 and 1977 several sites in south-east Scotland were surveyed for hybrids. Mass collections and morphometric measurements were made in the field. Principal components analysis and summary statistics were used to demonstrate the existence of an intermediate group of low fertility. A detailed comparison of plants at one site showed that for the putative hybrids the length of pollen grains and of leaf hairs on the lower epidermis of the leaf was discrete. The H. sphondylium x H. manteqazzianum cross set 23% seed which was 73% viable. Attempts to synthesize hybrids on H. mantegazzianum failed on six of nine plants, and gave an average 1% seed set. Both species set more seed on intraspecific crosses between plants, but on selfing H. sphondylium set only 16% seed, and H. mantegazzianum proved to be fully protandric within the primary umbel. Pollen transferred from secondary to primary umbels of the same H. manteqazzianum plant set 69. seed; there was no evidence of a self-incompatibility system, or inbreeding depression. In the field the flowering time of both parents and hybrids overlap. A single backcross on H. sphondylium with hybrid pollen gave 14% seed set which was 77% viable, but from the survey there was no noticeable increase in variation between pure and mixed populations of either species that might indicate introgression. Putative hybrids were rare, and only found where populations of both species grew interspersed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662452 |
| Date | January 1979 |
| Creators | Stewart, Fiona |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11429 |
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