populus genus --- Willow family
narrowleaf cottonwood (Populus angustifolia) -- in March -- Ross, Fort Collins Natural Area, CO green & brown
narrowleaf cottonwood (Populus angustifolia) -- in April -- Arapaho Bend, Fort Collins Natural Area, CO
narrowleaf cottonwood (Populus angustifolia) -- in September -- Red Mountain Open Space, Larimer County, CO
eastern cottonwood (Populus deltoides) -- in May -- Gustav Swanson, Fort Collins Natural Area, CO green & brown
eastern cottonwood (Populus deltoides) -- in April -- Arapaho Bend, Fort Collins Natural Area, CO green & brown
eastern cottonwood (Populus deltoides) -- in February -- River's Edge, Fort Collins Natural Area, Larimer County, CO
eastern cottonwood (Populus deltoides) -- in September -- Boyd Lake State Park, Larimer County, CO
quaking aspen (Populus tremuloides) -- in September -- Williams, Fort Collins Natural Area, Larimer County, CO
quaking aspen (Populus tremuloides) -- in October -- Old Flowers Road, Larimer County, CO green & brown
lanceleaf cottonwood (Populus x acuminata) -- in September -- Well Gulch Nature Trail, Lory State Park, CO green & brown