Thallus color

A smaller percentage of the Phaeophyta (59% of taxa) contain MAAs and concentrations in thalli are relatively low (<300 nmol mg-1 protein). The Phaeophyta also excrete colored compounds with UV-absorbing properties.62 Some of these exudates are polyphenolic substances that are usually associated with alleopathy. However, in Ascophyllum nodosum, thallus concentrations are regulated by UV exposure and small herbivores are not deterred, rather they feed preferentially on irradiated algae.59 Since the Chlorophyta and Phaeophyta successfully inhabit intertidal and shallow subtidal areas, they have apparently evolved very efficient protective and repair mechanisms for dealing with UV exposure, but MAAs are probably not the key to their fitness in high light environments. 

For example, various types of rock and rock crystals influence the thickness, form, and sometimes color of tissues of endolithic crusts (Doppelbauer, 1959). Similarly, Hertel (1967) noted that the harder the rock, and/or the lower the calcium content, the greater the tendency for a normally endolithic species to form an epilithic thallus. 

Observations around point sources in Britain suggest that they produce lichen deserts, the margins of which are frequently characterized by damaged thalli, e.g., chalky white L. conizaeoides or Parmelia saxatilis and P. sulcata which show abnormal pink, white, or brown coloration in the thallus. These colors which may to some extent be reversible are caused by sublethal fumigations associated with abnormal weather conditions or an unusually heavy exposition of pollutants. The edge of deserts associated with powerful point sources are thus not in as complete a state of equilibrium as urban deserts where pollution levels are more stable. 

Ascocarps lirelliform, not bordered by thallus. Receptacle often carbonized. Asci not amyloid. Spores two-celled, thin-walled, colorless to mostly colored, often verrucose, the cells not lens-shaped. Pycnospores long. Algae trentepohlioid. On various substrates. 

Thallus crustose, squamulose, foliose, or fruticose, variously colored. Apothecia sessile, rarely sunken, biatorine to lecideine or lecanorine with a more or less distinct amphithecium. Paraphyses simple or branched, as a rule with thickened tips, often anastomosing. Asci more or less clavate, moderately thick-walled, 1+ blue, with a distinct 1+ blue tholus. Spores normally to eight, mostly two-celled, less commonly multicellular and muri-form, unicellular only in a few at least partially derived groups, often thick-walled with complex wall structure. Fulcra short-celled. Pycnospores short... 

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