1. Old World aspen with a broad much-branched crown; northwestern Europe and Siberia to North Africa
   - quaking aspen, Populus tremula

Type of: aspen

• suborder Microchiroptera
• suborder Mugiloidea
• suborder Myomorpha
• suborder Mysticeti
• suborder Myxiniformes
• suborder Myxinoidei
• suborder Natantia
• suborder Nematocera
• suborder Nothosauria
• suborder Odontoceti
• suborder Ophidia
• suborder Ornithomimida
• suborder Ornithopoda
• suborder Oscines
• suborder Osteostraci
• suborder Otides
• suborder Pachycephalosaurus
• suborder Passeres
• suborder Percoidea
• suborder Petromyzoniformes
• suborder Pinnipedia
• suborder Plesiosauria
• suborder Prosauropoda
• suborder Prosimii
• suborder Reptantia