Petrova O. The lichen genus Usnea in eastern Gennoscandia. III Shrubby species. Ann. Bot. Fennici. 1999, 36, p. 235-256.

ANN. BOT. FENNICI 36 (1999) • Usnea in East Fennoscandia. III. 239 present on pines in hypermaritime regions of Nor- way (Clerc 1987a), while the relatively xerophytic species U. hirta is the only common Usnea on pines in East Fennoscandia. Most of the East Fen- noscandian Usnea species are more or less hygro- philous and photophilous, and therefore they are most frequent in moist, well-lit sites, but they have quite wide ecological amplitude and may also oc- cur near farms, in parks and in other man-made habitats. Usnea glabrescens , however, is more restricted to old-growth forests than the other shrubby species. Usnea is a cosmopolitan genus occurring in all continents. The East Fennoscandian Usnea flora mostly consists of species that are widely distributed in the Northern Hemisphere, but also contains some species that are nearly cosmopoli- tan being also found in the Southern Hemisphere. The genus is probably phylogenetically very old and many of the species seemingly have reached their present wide world distribution during a long period, in which they have adapted to different habitats and climates. East Fennoscandia mainly belongs to the boreal vegetation zone, in which coniferous for- ests are prevailing, except in the northernmost veg- etation zones. In the majority of the East Fenno- scandian areas, the climate is relatively oceanic in terms of temperature but less so in humidity conditions. The relatively low hygric oceanity is indicated by the absence of hypermaritime Usnea species, e.g., U. cornuta Körb. and U. fragilescens Lynge ( see Clerc 1987a, Halonen et al. 1998), in the area. All Usnea species have a more or less south- ern distribution in East Fennoscandia. Usnea hirta , U. lapponica and U. subfloridana are the only shrubby species that have been found occasion- ally in the northernmost regions. The front of the frequent occurrence of the genus roughly follows the northern limit of theMiddle Boreal bioclimatic zone ( see Ahti et al. 1968). Most of the species have a wide range in East Fennoscandia occur- ring both inwestern and eastern regions, but U. gla- brata represents an eastern element in the area, although less distinctly than U. longissima ( see Halonen 1997). However, the distribution of the Usnea species in Russia is very insufficiently known, since many regions are poorly studied. The best known Russian area is the western shore of Lake Ladoga, which has mainly been studied by V. Räsänen. CHEMISTRY Identifications of secondary compounds give a considerable help in the determination of Usnea specimens, because most of the species are very variable in morphology and different species may be morphologically overlapping. Most of the chemical compounds found in Usnea were not known to Motyka (1936–1938), but they were mainly detected by Y. Asahina and later chemists and chemotaxonomists. Early taxonomists did use certain colour reagents, which are often not spe- cific enough, however. All Usnea species occurring in East Fenno- scandia contain a yellow pigment, usnic acid, in the cortex. The medulla has a much more com- plex chemistry (Table 2) containingmainly closely related β -orcinol depsidones, e.g., norstictic, stictic, psoromic, protocetraric and salazinic ac- ids, or β -orcinol depsides, e.g., thamnolic, squa- matic and barbatic acids. Also present are fatty acids, including caperatic acid and the murolic acid complex. Terpenoids, e.g., zeorin, are found in every shrubby Usnea species in East Fenno- scandia, and they are especially common in U. ful- voreagens in which terpenoids have been found in almost every studied specimen. Furthermore, several unknown substances were found, but gen- erally they are not mentioned in the section “Tax- onomy”, since they are not taxonomically impor- tant. Salazinic acid is the most common secondary substance in the East Fennoscandian species. Nor- stictic acid is also relatively often present, whereas the other compounds of the stictic acid group (incl. connorstictic, stictic, constictic and cryptostictic acids) and protocetraric acid, for example, are less common and/or are often accessory. Many Usnea species produce different chemo- types in different areas, but the same species may also have several strains in one locality. Chemo- types occurring in other regions of Europe are mentioned in the section “Taxonomy”. The chem- istry of Usnea in other parts of the world has been investigated, e.g., byAsahina (1956), Clerc (1997), Clerc and Herrera-Campos (1997), Halonen et al.