Alnus Glutinosa

Source: Wikipedia
Family: Betulaceae
Genus: Alnus
Species: The genus comprises about 30 species of monoecious trees and shrubs, few reaching large size, distributed throughout the North Temperate zone, and in the New World also along the Andes southwards to Chile.
Plant Description:

The leaves are deciduous (not evergreen), alternate, simple, and serrated. The flowers are catkins with elongate male catkins on the same plant as shorter female catkins, often before leaves appear; they are mainly wind-pollinated, but also visited by bees to a small extent. They differ from the birches (Betula, the other genus in the family) in that the female catkins are woody and do not disintegrate at maturity, opening to release the seeds in a similar manner to many conifer cones.

The best-known species in Europe is the Common or Black Alder (A. glutinosa), native to most of Europe and widely introduced elsewhere. The largest species is Red Alder (A. rubra), reaching 35 m (the tallest is 32 m) on the west coast of North America, with Black Alder and Italian Alder (A. cordata) both reaching about 30 m. By contrast, the widespread Green Alder (A. viridis) is rarely more than a 5 m shrub.

The common name alder is derived from an old Germanic root. The botanic name Alnus is the original Latin name. Both the Latin and the Germanic derive from the proto-Indo-European root el-, meaning 'red, brown,' which is also the ultimate root for the English words elk and elm --a tree more distantly related to the alders.

Classification: The genus is divided into three subgenera:

Subgenus Alnus.
Trees. Shoot buds stalked. Male and female catkins produced in autumn (fall) but staying closed over winter, pollinating in late winter or early spring. About 15-25 species, including:
Alnus acuminata - Andean Alder. Andes Mountains, South America.
Alnus cordata - Italian Alder. Italy.
Alnus cremastogyne
Alnus glutinosa - Black Alder. Europe.
Alnus incana - Grey Alder. Europe & Asia.
Alnus oblongifolia (A. incana subsp. oblongifolia) - Arizona Alder. Southwestern North America.
Alnus rugosa (A. incana subsp. rugosa) - Speckled Alder. Northeastern North America.
Alnus tenuifolia (A. incana subsp. tenuifolia) - Thinleaf Alder or Mountain Alder. Northwestern North America.
Alnus japonica - Japanese Alder. Japan.
Alnus jorullensis - Mexican Alder. Mexico, Guatemala.
Alnus nepalensis - Nepalese Alder. Eastern Himalaya, southwest China.
Alnus orientalis - Oriental Alder. Southern Turkey, northwest Syria, Cyprus.
Alnus rhombifolia - White Alder. Interior western North America.
Alnus rubra - Red Alder. West coastal North America.
Alnus serrulata - Hazel alder, Tag or Smooth alder. Eastern North America.
Alnus subcordata - Caucasian Alder. Caucasus, Iran.

Subgenus Clethropsis.
Trees or shrubs. Shoot buds stalked. Male and female catkins produced in autumn (fall) and expanding and pollinating then. Three species:
Alnus formosana -Formosan Alder Taiwan
Alnus maritima - Seaside Alder. East coastal North America, plus disjunct population in Oklahoma.
Alnus nitida - Himalayan Alder. Western Himalaya.

Subgenus Alnobetula.
Shrubs. Shoot buds not stalked. Male and female catkins produced in late spring (after leaves appear) and expanding and pollinating then. One to four species:
Alnus viridis - Green Alder. Widespread:
Alnus viridis subsp. viridis. Eurasia.
Alnus viridis subsp. maximowiczii (A. maximowiczii). Japan.
Alnus viridis subsp. crispa (A. crispa). Northern North America.
Alnus viridis subsp. sinuata (A. sinuata, Sitka Alder or Slide Alder). Western North America, far northeastern Siberia

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