The dual nature of lichens was first hinted at by de Bary (1866) and clearly recognized by Schwendener (1867). A lichen is now defined as a ‘self-supporting association of a fungus (mycobiont) and a green alga or cyanobacterium (photobiont)’ (Kirk et al., 2001), ‘resulting in a stable thallus of specific structure’ (Ahmadjian, 1993). The fungal partner usually contributes most of the biomass to this symbiosis, including the external surface. It is thus termed the exhabitant, whereas the unicellular or filamentous photobiont cells are collectively called the inhabitant because they are located inside the lichen thallus (see Ahmadjian, 1993). Most lichens have a characteristic appearance which permits their identification if suitable keys are available (e.g. Purvis et al., 1992; Wirth, 1995a, b; Brodo et al., 2001). Since the structure of lichens is almost entirely due to the fungal partner, lichen taxonomy is synonymous with the taxonomy of the mycobiont.

Throughout this book we have attempted to consider fungi showing predominantly or purely asexual reproduction together with their known or suspected teleomorphs. However, certain groups of taxonomically diverse fungi colonizing the same specialized habitats or substrates are best understood in their ecological context, especially if they show strikingly similar adaptations and morphology despite their different evolutionary histories. Two cases illustrating such convergent evolution among anamorphic fungi are the nematophagous habit and the aquatic habitat, which we shall consider in turn in this chapter.

Following extensive re-arrangements, the class Urediniomycetes (about 8000 species) is now considered to be monophyletic, although the naming of orders and families is still proving difficult (Swann & Taylor, 1995; Kirk et al., 2001; Swann et al., 2001). The order Uredinales (rust fungi) is by far the largest (about 7000 species) and the most important. The order Microbotryales, although taxonomically part of the Urediniomycetes, is a group of fungi causing smut diseases and will be discussed in Chapter 23. Many Urediniomycetes belonging to several orders occur predominantly in the yeast state. An important group, the Sporidiales, contains the red yeasts Sporidiobolus and Rhodosporidium (anamorphs Sporobolomyces and Rhodotorula, respectively), and this order is considered in more detail on pp. 666–670.

‘Basidiocarps of Auricularia can be stored dry, discharging ballistospores upon rehydration. This article describes methods to demonstrate basidiospore germination by repetition or formation of a primary mycelium and/or microconidia’

It is well known that many fungi are host-specific, i.e. their fruiting is restricted to one host plant or a group of closely related hosts. An example is Hypoxylon fragiforme whose perithecial stromata are common on dead trunks and branches of beech, Fagus sylvatica (Fig 1), but are only occasionally found on other woody hosts. Mycelium of H. fragiforme is present mainly in the sapwood rather than the bark of branches of healthy beech trees, and this fungus has therefore been called a xylotropic endophyte (Chapela, 1989). Colonization is not extensive so long as the water content of infected host tissue remains high, but if branches are cut from living trees and allowed to dry, the mycelium extends rapidly (Chapela & Boddy, 1988a,b; Chapela, 1989).

Names of fungi1. Sclerotinia curreyana (Berkeley ex Currey) P. Karsten = Myriosclerotinia curreyana (Berkeley ex Currey) Buchwald; conidial state Myrioconium Sydow2. Sclerotinia Fuckeliana (de Bary) Fuckel = Botryotinia fuckeliana (de Bary) Whetzel; conidial state Botrytis cinerea Persoon ex Fries3. Sclerotinia fructigena (Persoon) Schröter = Monilia fructigena Honey ex Whetzel; conidial state Monilia fructigena (Persoon) EatonIntroduction: Features of interestMembers of the Sclerotiniaceae are plant pathogens characterized by stalked apothecia with inoperculate asci. Apothecia arise from stromata, e.g. sclerotia which are formed on or in the tissue of the host plant. The apothecial state and the type of stroma are typical and taxonomically relevant features of the Sclerotiniaceae, and the family has been supported and delimited by DNA sequence data (Carbone & Kohn, 1993; Holst-Jensen et al., 1997a,b).

Name of fungusTeleomorph: Rhytisma acerinum (Pers.) Fr. (order Rhytismatales, family Rhytismataceae)Anamorph: Melasmia acerina Lév.Introduction: Features of interestTar-spot disease on leaves of sycamore (Acer pseudoplatanus L.) is one of the most easily recognised foliar plant diseases caused by a fungus (Figs 1 and 4). First described by Elias Fries in 1823, knowledge of it had become well-established by the latter half of the 19th century (e.g. Berkeley, 1860; Massee, 1915). The causal fungus, Rhytisma acerinum, occurs in Europe and North America on A. pseudoplatanus throughout its distribution range and also on other species of Acer (Sutton, 1980; Farr et al., 1989), but it is less frequent in urban and industrial areas.The black tar-spots visible in late summer and autumn are stromata containing many apothecial rudiments, but these only mature to form asci during the winter on fallen leaves (Jones, 1925; Duravetz & Morgan-Jones, 1971). Maturing apothecial stromata develop linear or convoluted ridge-like swellings which raise the thick black layer (clypeus) on the upper surface of the stroma (Fig 1). Eventually, the surface breaks along the ridges (Fig 2), exposing a greyish hymenium (Fig 3) which contains club-shaped asci and filamentous paraphyses with curved or recoiled tips (Figs 8 and 9). The ascospores are unicellular and needle-shaped, with an apical mucilage pad (Fig 10). In Britain and Europe, ascospore discharge from overwintered stromata takes place in March and April, just as the new sycamore leaves unfold.

After incubation on moist filter paper, Podosordaria tulasnei frequently formed sterile stromata on rabbit pellets collected from the field. These developed extensive submerged rhizomorph systems when pellets were incubated on sand, but further differentiation and sexual reproduction occurred only when pellets bearing such structures were buried in soil. The present report describes the development of subterranean rhizomorphs, which are rare among ascomycetes, and the production of mature perithecial stromata. Podosordaria tulasnei is a true coprophilous fungus but, like some other members of the genus, has a high capacity to explore the surrounding soil. No anamorphic state was found in our material or in pure culture.

We report the recent widespread occurrence in Britain of Puccinia distincta, a rust fungus on wild and cultivated daisies (Bellis perennis). The rust is short-cycled, with only aecia and telia on Bellis, and may be of Australian origin. It is very similar to, and possibly derived from, the macrocyclic P. obscura, a rust indigenous to Britain which produces pycnia and aecia on Bellis and uredinia and telia on Luzula. However, it differs from another Australian introduction, the groundsel rust (P. lagenophorae). The disease caused by P. distincta is so severe that it seriously impairs growing of ornamental daisies.