title: Taxonomic and ecological studies on the genus Orobanche L. in the British Isles
Creators: name: Jones, Michael
Publisher: name: University of Liverpool Repository
Year: 2023

description: This thesis is a study of the cultivation, taxonomy, comparative morphology, reproductive biology, ecology and conservation of the native members of the genus Orobanche (Broomrapes) in the British Isles. The study was prompted by an absence of ecological information on the genus and the difficulty in identifying some species. Information on host range, distribution, habit, habitat, phenology and morphological variation is discussed in detail for each of the nine native species. Broomrapes are found in a wide range of habitats, excluding montane and wetlands, they are lowland plants, most having a southern distribution. O. minor and O. hederae are common, but the remaining species are declining and five are protected by law. Conservation work with broomrapes is in its infancy and there are no established methods whereby species can be successfully introduced into selected areas. Experiments in transplanting O. rapum-genistae tubers failed and in vitro seed germination was only successful in O. hederae. An attempt was made to cultivate all of the native species. Successful cultivation was not difficult, but was time consuming because most species are biennial. Only between 0.35-1.1% of seeds sown are able to develop to flowering. No physiological strains, adapted to parasitize a specific host or range of hosts were detected, although it was not always possible to infect known hosts. Apart from overall stature and number of flowers, there was little evidence to suggest that the host was able to influence the parasite's morphology. Some large and densely flowered species are visited by insects, particularly Bombus and Vespula species, but evidence from floral structure, floral colouration and ultra-violet light studies showed that broomrapes are not highly attractive to insects. Most species are autogamous, although O. rapum-genistae is self-incompatible. Detailed information is given on seed length, weight and seed production and viability. Seeds are small, long lived and produced in large numbers. Detailed morphological studies were carried out to assess the value of accepted taxonomic characters and to investigate certain character not previously studied. Stomatal studies and seed morphology were of limited taxonomic use, although a difference in pollen morphology between members of the sections Trionychon (elliptic, trizonocolpate) and Orobanche (sub-spherical, nonaperturate) was observed. In order to resolve any major correlated trends in the morphological variation within O. minor s. l. 29 metric and scalar characters were measured from ten individuals from each of 21 populations and analysed using multivariate clustering and discriminating methods. The results indicated that O. minor var. flava should be reduced to f. flava and the data did not support retaining the rank of O. minor var. compositarum. No discontinuous variation was found between O. minor and O. maritima and the specific rank of the latter was not supported, although Orobanche plants on maritime hosts (referable to O. maritima) often have a longer corolla tube and are of greater stature. The production and cultivation of F1 hybrids within O. minor and between O. minor and O. reticulata were successful. The hybridization between O. minor and O. hederae showed the existence of a partial breeding barrier and seed production was low. Several other hybridizations were unsuccessful.