The geographic range of the genus Picea A. DIETR. is restricted to the northern hemisphere. Taxa of this genus occur between 71oN latitude in North America and Eurasia to 32°N in North America and 23oN in Southeast Asia (Fig. 4.1). The range is divided into two parts and is considered a classical example of a euroasiatic-North American intercontinental disjunction. Large portions of the range of the genus are occupied by P. obovata LEDEB.1 in Asia, P. abies (L.) KARST. in Europe, and P. glauca (MOENCH) VOSS and P.mariana (MILL.) Britt. in North America. As a rule, the northern species cover extensive areas and form forests, whereas the southern taxa generally have restricted distributions in the mountains and many are relicts.
Nine spruce species occur in North America (Table 1). Picea glauca and P mariana are the most economically important species. These species form forests throughout much of Canada and the northernmost regions of the United States. In the northeastern United State, Picea rubens SARG. is also an important spruce species. It grows in the Appalachian Mts up to an altitude of about 2000 m. P. sitchensis (BONG.) CARR. occurs in western North America and attains an altitude of 1000 m, while P. engelmannii (PARRY) ENGELM. and P. pungens ENGELM. occur at altitudes of up to of 3700 m in the Rocky Mts Taxa exhibiting limited ranges in the North America are P. breweriana S. WATS in northern California, P. mexicana MARTINEZ and P. chihuahuana MARTINEZ in northern Mexico. The latter two species mark the southern limit of the range of Picea in Central America and attain an altitude of 2800 m in the Sierra Madre (HARLOW and HARRAR1950; FOWELLS1965; LITTLE1971; HARTMUT 1976; WENG and JACKSON 2000).
In Europe the geographic range of the genus is largely comprised of the species Picea abies. The remaining European species are P. obovata in the northeastern part of the continent (SOKOLOV et al. 1977) and a relict P. omorica
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