David J. Hill

David J. Hill

Lichen growth is reviewed in the context of the anatomy of the growth region, thallus morphology of crustose and foliose lichens, photosynthesis, mathematical models and their application. The Aplin & Hill model is suggested as a basis for more detailed investigation of integrated processes of growth including not only the size increase but also the general structure of the thallus and the processes which limit growth.

Kerry Stoker; David T. Cooke; David J. Hill

In woad (Isatis tinctoria), field observations indicated, that after periods of dry sunny weather, indigo yields increased significantly, suggesting that light intensity and quality affected indigo precursor production. Therefore, woad was grown under different light intensities and in the presence or absence of supplementary UV light. In general, plants supplied with more light produced more indigo than those given lesser light. When plants under greater light regimes were transferred to lesser light conditions, then indigo production declined. The opposite was also true, indicating that greater indigo production can be obtained from plants harvested after periods of increased sunlight.

David J. Hill

It is proposed that lichen photobionts, compared to mycobionts, have very limited capacity to evolve adaptations to lichenization, so that the symbionts in lichens do not co-evolve. This is because lichens have (a) no sequential selection of photobiont cells from one lichen into another needed for Darwinian natural selection and (b) no photobiont sexual reproduction in the thallus. Molecular studies of lichen photobionts indicate no predictable patterns of photobiont lineages that occur in lichens so supporting this proposal. Any adaptation by photobionts accumulating beneficial mutations for lichenization is probably insignificant compared to the rate of mycobiont adaptation. This proposal poses questions for research relating the photobiont sexual cycle (genetic and cellular), the fate of photobiont lineages after lichenization, whether lineages of photobionts in thalli change with time, thallus formation by from spores as well as carbohydrate movement from photobionts to mycobionts and regulation of co-development of the symbionts in the thallus.

David J. Hill

Growth of an organism can be defined as the increase in its living biomass. In lichens, biomass increase is presumed to be manifest in an increase in linear dimension, area or weight, which are convenient to measure (Table 1). However they do have different interpretations. For a lichen, an increase in lobe length, or thallus diameter, may not exactly reflect increase in area or mass; conversely, biomass increase may, for example, occur without an increase in the apparent linear size of a lichen thallus (e.g. a thallus confined in a mosaic may grow only in thickness). The rate of growth, which is expressed as increase per unit time, may give very different rates over different time spans, if it varies with different sized thalli, and, especially, with differing environments. The time span can be predetermined and the size of thallus can be allowed for in the analysis of the data. The growth form of the thallus is also important in deciding what parameter to measure. The type of data analysis planned and the aim of the study may also determine the type of measurement chosen. It should be decided whether the actual direct measurement itself is required or a derived measure, such as a proportional increase or the value of a growth rate coefficient.

Cécile Gueidan; David J. Hill; Jolanta Miadlikowska; François Lutzoni

Lecanoromycetes is the class of Ascomycota with the largest number of lichen-forming fungi. Members of this class are important components of most terrestrial ecosystems and occur in various habitats and on different substrates, from tropical to polar regions. Morphological, anatomical, and chemical characters have traditionally been used to classify orders, families, and genera within Lecanoromycetes. In the last two decades, molecular phylogenies have shown that traditional classification systems were not always consistent with the evolutionary history of this fungal class, resulting in changes in the delimitation of orders and families. Here, we revisit the taxonomic value of the main characters traditionally used for classification in light of current molecular phylogenies. The current delimitation of the 14 orders of Lecanoromycetes is also discussed, and recent changes in classification are highlighted.

Kerry Stoker; David T. Cooke; David J. Hill

David J. Hill

David J. Hill; Per M. Jørgensen; André Aptroot

Holger Thüs; David J. Hill

Cathy Badley; David J. Hill; Nicholas Wray