According to observations of naturalists and beekeepers.
Where are you?
This plant is present in at least 13 states/provinces in this country.
Acer negundo (aka: Boxelder, Western boxelder, Arizona boxelder, California boxelder, Texas boxelder, Interior boxelder, Violet boxelder)
Pyrus communis (aka: European pear, Common pear)
Acer glabrum (aka: Rocky Mountain maple, Douglas maple, Greene's maple, New Mexico maple, Torrey maple)
Salix lucida (aka: Shining willow, Greenleaf willow, Tail-leaf willow, Whiplash willow, Pacific willow, Lance-leaf willow, Longleaf willow, Red willow, Western shining willow)
Rubus spectabilis (aka: Salmonberry)
Salix discolor (aka: Pussy willow, American pussy willow, Glaucous willow, Large pussy willow)
Salix exigua (aka: Narrowleaf willow, Coyote willow)
Prunus cerasus (aka: Sour cherry, Tart cherry, Dwarf cherry, Montmorency cherry)
Crataegus douglasii (aka: Black hawthorn, Douglas hawthorn, River hawthorn, Western thornapple)
Populus tremuloides (aka: Quaking aspen, Trembling aspen, Aspen, American aspen, Mountain aspen, Golden aspen, Trembling poplar, White poplar, Popple, Alamo Blanco)
Salix scouleriana (aka: Scouler's willow, Upland willow)
Acer circinatum (aka: Vine maple)
Prunus emarginata (aka: Bitter cherry)
Malus fusca (aka: Oregon crab, Oregon crab apple, Pacific crab apple, Western crab apple)
Salix arbusculoides (aka: Littletree willow)
Salix bebbiana (aka: Bebb willow, Beak willow, Beaked willow, Long-beaked willow, Diamond willow, Chaton, Petit Minou, Smooth Bebb willow)
Malus domestica (aka: Pyrus pumila, Malus pumila, Apple)
Acer macrophyllum (aka: Bigleaf maple, Big-leaf maple, Oregon maple)
Acer platanoides (aka: Norway maple)
Rubus ursinus (aka: California blackberry, California dewberry, California grapeleaf dewberry, Douglasberry, Pacific blackberry)