According to observations of naturalists and beekeepers.
Where are you?
This plant is present in at least 13 states/provinces in this country.
Blueberry willow's two varieties differ significantly in growth form. Low blueberry willow is a much-branched, low-growing, and often prostrate shrub typically between 8 and 24 inches (20-60 cm) tall. Tall blueberry willow is an erect shrub often 6 to 8 feet (2.0-2.5 m) tall but is occasionally taller. Both varieties have relatively small, simple, alternate, deciduous leaves. Male and female flowers occur on separate plants in 3/4- to 2-inch-long (1.5-5 cm) erect or ascending catkins. The fruit is a two-valved capsule.
In Alaska, low blueberry willow catkins appear after the leaves have begun to develop. Seeds are dispersed during the growing season, about mid-June.
In Alaska, tall blueberry willow catkins appear after the leaves have begun to develop. Flowering is in early to mid-June, seeds mature in late June to mid-July, and catkins fall in late July.
Salix monticola (aka: Park willow, Cherry willow, Mountain willow, Serviceberry willow, White willow)
Salix geyeriana (aka: Geyer willow, Silver willow)
Rhus glabra (aka: Smooth sumac, Common sumac, Rocky Mountain sumac, Red sumac, Western sumac, White sumac)
Rubus laciniatus (aka: Cutleaf blackberry, Evergreen blackberry, Slashed blackberry)
Salix bebbiana (aka: Bebb willow, Beak willow, Beaked willow, Long-beaked willow, Diamond willow, Chaton, Petit Minou, Smooth Bebb willow)
Brassica napus (aka: Rapeseed)
Allium schoenoprasum (aka: Chives)
Sinapis arvensis (aka: Charlock mustard, California rape, Charlock, Corn mustard, Canola, Kaber mustard, Rapeseed mustard)
Asclepias tuberosa (aka: Butterflyweed, Butterfly Milkweed, Orange Milkweed, Pleurisy Root, Chigger Flower, Canada root, Fluxroot, Indian paintbrush, Indian posy, Orange root, Orange Swallow-wort, Tuber root, Yellow milkweed, White-root, Windroot, Butterfly love)
Salix brachycarpa (aka: Shortfruit willow, Barren-ground willow, Small-fruit sand dune willow, Small-fruit willow)
Rubus idaeus (aka: Raspberry, Black-haired red raspberry, Brilliant red raspberry, American red raspberry, Red raspberry, Smoothleaf red raspberry, Wild raspberry, Wild red raspberry, Grayleaf raspberry)
Rubus parviflorus (aka: Thimbleberry, Western thimbleberry)
Amorpha fruticosa (aka: Desert false indigo, False indigo-bush, Bastard indigobush, Indigo Bush)
Brassica rapa (aka: Field mustard, Common mustard, Wild mustard, Wild turnip, Forage turnip, Wild rutabaga, Birdsrape mustard, Rape mustard)
Cirsium arvense (aka: Creeping Thistle, Canada thistle, Field thistle, California thistle, Lettuce from hell thistle, Corn thistle, Cursed thistle, Green thistle, Hard thistle, Perennial thistle, Prickly thistle, Small-flowered thistle, Way thistle, Stinger-needles)
Echium vulgare (aka: Viper's bugloss, Blueweed, Blue thistle)
Rubus armeniacus (aka: Himalayan blackberry, Rubus discolor, Rubus procerus)
Chamaenerion angustifolium (aka: Fireweed, Great willowherb, Rosebay willowherb, Saint Anthony's Laurel, French-willow)
Agastache foeniculum (aka: Giant hyssop, Blue giant hyssop, Anise hyssop, Fragrant giant hyssop, Lavender giant hyssop)
Hyssopus officinalis (aka: Hyssop)