Alder - Classification

Classification

The genus is divided into three subgenera:

Subgenus Alnus: Trees with stalked shoot buds, male and female catkins produced in autumn (fall) but stay 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 firma—Kyūshū (Japan)
• Alnus glutinosa—black alder, Europe

• Alnus incana—grey alder, Eurasia
  • Alnus hirsuta (A. incana subsp. hirsuta)—Manchurian alder, northeastern Asia, and central Asia in mountains
  • 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 or mountain alder, northwestern North America
• Alnus japonica—Japanese alder, Japan
• Alnus jorullensis—Mexican alder, Mexico, Guatemala (one of the few evergreen species)
• Alnus mandshurica— Russian Far East, China, Korea
• Alnus matsumurae—Honshū (Japan)
• Alnus nepalensis—Nepalese alder, eastern Himalaya, southwest China
• Alnus orientalis—Oriental alder, southern Turkey, northwest Syria, Cyprus
• Alnus pendula—Japan, Korea
• Alnus rhombifolia—white alder, interior western North America
• Alnus rubra—red alder, west coastal North America

• Alnus serrulata—hazel alder, tag alder or smooth alder, eastern North America
• Alnus sieboldiana—Honshū (Japan)
• Alnus subcordata—Caucasian alder, Caucasus, Iran
• Alnus trabeculosa—China, Japan

Subgenus Clethropsis. Trees or shrubs with stalked shoot buds, 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 wit 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