The evolution of multicellularity paved the way for significant increases in biological complexity. Although multicellularity has evolved many times independently, we know relatively little about its origins. Directed evolution is a promising approach to studying early steps in this major transition, but current experimental systems have examined only a subset of the possible evolutionary routes to multicellularity. Here we consider egalitarian routes to multicellularity, in which unrelated unicellular organisms evolve to become a multicellular organism. Inspired by microbial syntrophies and lichens, we outline three such routes from a system of different species to an interdependent relationship that replicates. We compare these routes to contemporary experimental systems and consider how physical structure, the threat of invasion, division of labour and co-transmission affect their evolution.

In a recent treatment of the Pannariceae of Ecuador, Jørgensen & Arvidsson (2004: 131) pointed out the surprising absence of the genus Fuscopannaria in Ecuador, a genus which is rather common, with many species, in the Pacific Northwest of North America (Jørgensen 2001). The authors claim that, on the western side of the Americas, the genus appears to stop north of Mexico, only to reappear in southern Chile and Argentina. While going through his material, the second author discovered two specimens belonging in this genus from Mexico and Ecuador, which contradicts that statement. Both are typical Fuscopannaria leucosticta specimens (Fig. 1), the type species of the genus originally described from eastern North America (Jørgensen 2001: 684), and fairly widely distributed in warm temperate parts there, and extending as far south as Cuba (Fig. 2).

The genus Arthopyrenia is redefined to include only corticolous lichenized or non-lichenized fungi. A key and notes are provided for the 14 species accepted for the British Isles, including three new species, A. carneobrunneola, A. ranunculospora and A. viridescens. Arthopyrenia nilescens is resurrected from synonymy, A. cinereopruinosa is confirmed as occurring in the British Isles, and A. fraxini, A. salicis and A. subcerasi are added to the British list. The following names are lectotypined: Arthopyrenia fraxini Massal. (including f. orbicularis Massal. and f. rufidula Massal.), A. salicis Massal., Verrucaria nitescens Salwey and V. subcerasi Vainio.

The species of Arthonia s. lat. (Arthoniales, Ascomycotina) lichenicolous on species of Pseudocyphellaria and other Lobariaceae are revised. Thirteen species are accepted, and eight species are described as new (all from the Southern Hemisphere): Arthonia badia Wedin & Hafeliner, A. coriifoliae Wedin & Hafeilner, A. fiavicantis Wedin & Hafellner, A. maculiformis Wedin & Hafeliner, A. minuta Wedin & Hateliner, A. santessoniana Wedin & Hafellner, ‘A.’ semi-immersa Wedin & Hafeilner, and A. subaggregata Wedin & Hafellner. Comparative notes on additional accepted species previously described from Pseudocyphellaria or other Lobariaceae (A. pelvetii, A. plectocarpozdes, A. pseudocyphellariae, A. stzctaria, and A. subconveniens) are included, and a key to the Arthonia (and similar) species growing on Lobariaceae is presented. The coelomycete genus Subhysteropycnis Wedin & Hafellner is described for the species S. maculiformans Wedin & Hafellner, the macroconidal anamorph of Arthonia badia. The lecanoralean genus Corticiruptor Wedin & Hafeliner is described as new to accommodate the single lichenicolous species C. abeloneae (P. M. Jørg.) Wedin & Hafellner comb. nov., and the additional new combination Plectocarpon linitae (R. Sant.) Wedin & Hafellner is proposed. The names Celidium pelvetii Hepp, Sticta aurata b abortiva Schaer. and Arthonia stictarza Nyl. are lectotypified, and the typifications are discussed.

The response of net photosynthesis, dark respiration and acetylene reduction to temperature, moisture and light intensity were examined for Stereocaulon virgatum growing in the cloud/shroud zone on the tropical volcano La Soufrière, Guadeloupe, French West Indies. Rates for both acetylene reduction and net photosynthesis were maximal at saturating water contents, a pattern attributed to the finely branched nature of the phyllocladoid branchlets and the exposed position of spherical cephalodia, both of which minimize the formation of surface and interhyphal water films. Under conditions typical of those during cloud/shroud periods (13–16°C), thalli of S. virgatum exhibit many characteristics seen in other shade-tolerant lichen species. Net photosynthesis was light saturated at 300 μmol m−2 s−1 PAR, while the photocompensation point was less than 25 µmol m−2 s−1 PAR. Net photosynthetic uptake of carbon dioxide was optimal at 27–34°C, at which point light saturation was near 700 µmol m−2 s−1 PAR and the photocompensation point between 50 and 100 µmol m−2 s−1 PAR. Thalli of S. virgatin exhibited temperature-dependent sensitivity to high insolation. Only at 20°C were thalli able to tolerate high light exposure without reduction of apparent quantum yield. Exposure to high light intensity at 40°C inhibited the apparent quantum yield by almost 40% and acetylene reduction by 95%. This suggests brief periods of insolation shock may exert an influence disproportionately higher than either their frequency or duration. Thalli are normally exposed to cloud/shroud conditions but net photosynthetic uptake was maximal only during periods of elevated thallus temperature experienced at the onset of an insolation shock. However, with prolonged high insolation exposure and further elevation of thallus temperatures and thallus desiccation, severe impairment of subsequent photosynthetic activity ensues. S. virgatum may be characterized as a shade-tolerant species but its physiology is more adapted in some respects to conditions experienced during rare periods of full insolation.

Two new lichen species Peltigera frippii Holt.-Hartw. and P. scabrosella Holt.-Hartw.are described. Their morphology, chemistry, and ecology are discussed, and their distribution in Norway is mapped. New chemical data are also given for the related species P. lyngei Gyelnik, P. malacea (Ach.) Funck, P. neckeri Müll. Arg., and P. scabrosa Th. Fr.

Pannaria isidiosa sp. nov. is newly described from montane forests in New South Wales, Australia. It is characterized by abundant globose to coralloid isidia, long-ellipsoid spores with a verrucose and citriform perispore. It is related to P. xanthomelana, but in addition to pannarin and porphyrilic acid, it contains methylplacodiolic acid and a chemosyndrome of four unidentified terpenoids.

Foliicolous lichens complete their life cycles upon non-deciduous leaves in humid tropical and subtropical environments. The anatomy of these lichens and its adaptations to this specialized niche have received only limited attention. The present work examines the structural organization in seven species of the Gomphillaceae that colonize palm leaves in south-west Florida, USA. Thalli with their leaf substratum were embedded in resin and examined with SEM in backscattered electron detection mode. All species showed a continuous, covering epilayer of fungal origin that consisted of relatively sparse, scattered cell lumina of reduced diameter connected by cell wall-derived material. Fungal cells were intermixed below this layer, with algal cells often resting directly on the substratum. Interactions between symbionts were mainly limited to wall-to-wall contacts without penetration. The epilayer showed continuity with the fungal prothallus at the perimeter of the thalli. Crystalline deposits in the upper portions of thalli were common, particularly in the species of Gyalectidium examined. All thalli were entirely epicuticular; some covered the stomata of the leaf beneath. It is suggested that the prominence of non-living wall materials and mineral crystals in thallus structure might serve to minimize the metabolic cost of fungal tissue in climates where warm temperatures at night result in higher rates of respiration.

Five Japanese species of the lichen genus Menegazzia are recorded. Menegazzia caviisidia Bjerke & P. James sp. nov. is characterized by numerous globose to dactyliform to narrowly obovate, hollow isidia, small conical perforations, and thamnolic acid as the major medullary constituent. It appears to be a rare species, so far known only from three localities on Honshu. The status of the primary species M. asahinae is elucidated. Menegazzia pedicellata Bjerke sp. nov. is a rare caperatic acid-containing species previously included in M. asahinae s. lat. Menegazzia asahinae s. str. has perforated margins of apothecia and contains the stictic acid complex. Menegazzia asahinae f. subimpertusa and M. pseudocyphellata are reduced to synonymy with M. asahinae s. str. Two sorediate species are known, viz. M. subsimilis and M. terebrata.

The new combination Lithographa skottsbergii (Zahlbr.) Fryday & Coppins is made for Enterostigma skottsbergii Zahlbr., described from the Juan Fernandez Islands off the coast of Chile. The species is known only from Chile but its geographical range is here extended to include maritime regions of south-west Chile. The distribution pattern of the Lithographa species with submuriform ascospores is also discussed.

Bacidia neosquamulosa Aptroot & van Herk, a new corticolous lichen species, is described from the Netherlands, where it seems to be rapidly spreading and where it is considered to be a neophytic species. It is also reported from Belgium and Great Britain. It resembles corticolous morphs of the rather variable B. arnoldiana, but differs from this and other species by the longer, conspicuously septate, filiform, curved, macroconidia, the longer ascospores and the squamuloseisidiate thallus.

Where two crustose lichen thalli meet at a ‘ truce ’ boundary theshape of the boundary can be used to evaluate models of how lichen growth rates change with thallus size. The application of this method to studies of intra- and interspecific competition are discussed.

The saxicolous Strigula fractans sp. nov. and S. rupestris sp. now are described from Lord Howe Island, New South Wales, Australia. A new combination, S. decipiens (Malme) P. M. McCarthy, is proposed for Porina decipiens Malme, and a key to the 17 saxicolous species of Strigula is provided.

Caloplaca cancarixiticola Nav. -Ros., Egea & Llimona (Teloschistales, Lichenes) is described as new. It is characterized by a lobate thallus weakly attached to the substratum, and narrowly ellipsoid or ellipsoid-fusiform ascospores, (14.5–) 16–22(–25) × (4–)4–5–6um3 with a narrow equatorial wall-thickening, only (1–) 2.5–3.5(–4) um wide. This new species, related to the Caloplaca aurea-group of the subgenus Gasparrinia, was found on cancarixite, an ultrapotassic rock, in a volcanic region of Albacete (SE Spain).

In order to obtain a complete picture of the factors determining spatial pattern in a saxicolous lichen community (or any other plant community) it is important to use a range of analytical techniques at a variety of scales. The Jonas Rockslide study is an example of this, and three analyses from this study are discussed here. Each scale gives a different perspective on the processes acting in the community. The largest scale shows that lichen distributions are correlated with attributes of whole rockfaces such as slope and aspect. The second analysis examines pattern at the scale of 10 cm to 20 cm grid points and shows that within a rockface are many micro-habitats, reflected in the pattern of occurrence of different lichen species at this scale. The smallest scale of analysis is a ‘nearest-neighbour’ analysis, which indicates that lichens sample their environment differently and have different ecological strategies. These processes ultimately act together to give the observed pattern in the community.

Omphalodiella patagonica Henssen gen. et sp. nov. is described from two Patagonian localities in Argentina. In habit the new lichen resembles some species of Acarospora in having brown, peltate thalli less than 3 mm wide with immersed apothecia. The ontogeny and structure of the apothecia and pycnidia correspond, however, to genera of the Parmeliaceae. The apothecia are provided with a meristematic, cupular exciple, and the amyloid asci contain 8 or less, ± globose spores. The short-celled conidiophores produce rod-shaped conidia of bayonet type. The thallus is provided with a narrow paraplectenchymatic upper and a broad prosoplectenchymatic, strongly gelatinized lower cortex. The thallus contains gyrophoric acid; the cortex contains ‘glomellifera brown ’.

Lobaria pulmonaria is a widespread epiphytic foliose lichen that exhibits a prominent reticulum, a structure that has a presumed role in mechanical support and water capture. Using photogrammetry, thallus topography was digitally modelled in three dimensions to calculate 3D surface area (A3D), which was consistently greater than areas extracted from projected images (A2D). The A3D:A2D ratio, a proxy for topographic three-dimensionality, was strongly correlated with both specific thallus mass (STM) and external water-holding capacity (WHCexternal), suggesting that the reticulum in L. pulmonaria extends hydration, photosynthetic activity and growth, following rainfall. Three-dimensionality was more pronounced in larger thalli, which is likely beneficial to liquid water-dependent internal cephalodia that occur more in older thalli and most often within the fovea.

The macrolichen flora on trees in the Algarve is described on the basis of an examination of 105 main sites in the period 1970–76. 103 lichens are reported from the 43 phorophyte species studied, and discussions of the ecology and distributional patterns provided.