According to observations of naturalists and beekeepers.
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Narrowleaf willow is a widely-distributed species of plains and lower elevations to lower montane habitats in western North America. It occurs from Saskatchewan to eastern British Columbia, south through the western United States to Texas, Baja California Norte, and Chihuahua. While widespread in the Rocky Mountain, Great Basin, and desert regions, narrowleaf willow occurs entirely east of the Cascade Range.
This plant is present in at least 16 states/provinces in this country.
Narrowleaf willow is a native, winter-deciduous shrub that grows up to 33 feet (10 m) tall. More commonly, narrowleaf willow is 6.5 to 20 feet (2-6 m) tall with many erect shoots. Individual stems arise singly or a few together and form large colonies from spreading roots. Lateral roots of narrowleaf willow produce root sprouts in profusion, often in long rows. These shoots elongate rapidly in spring. Narrowleaf willow also resprouts from the root crown.
Individual stems often only live 10 years, though some may reach 20 years. Shoot length, leaf length, number of leaves per shoot, and mean internode length all decrease with age.
Narrowleaf willow is alternately described as "deep-rooted" and shallow-rooted. Roots are woody and spreading, forming an extensive root system, especially with the development of large clones.
Narrowleaf willow leaves are linear to linear-elliptic and acute at both ends. Leaf size ranges from 0.8 to 6 inches (2-15 cm) long and 0.1 to 0.8 inch (3-20 mm) wide.
Narrowleaf willow produces flowers in catkins 0.6 to 4 inches (1.5-10 cm) long. Catkins are first produced with or just after leaves, though flowering may occur in succession throughout the summer.
Narrowleaf willow is both drought-resistant and very tolerant of flooding; it can withstand flooding for periods of 2 or more growing seasons.
Willows are very frost tolerant. Mature leaves and winter-dormant stems are capable of surviving temperatures of -4 oF (-20 oC) and -94 oF (-70 oC) respectively. However, frosts during the early growing season can cause severe damage to the fast-growing shoots. Temperatures <28 oF (-2 oC) will kill the elongation zone soon after exposure. Lateral buds below the damaged shoot rapidly form new shoots.
Narrowleaf willow flowers appear with or just after the leaves in mid- to late spring. Flower buds in willows are formed during the season prior to flowering and are likely activated by specific temperature thresholds or accumulated heat units; however, narrowleaf willow also initiates flowers at the tips of current shoots throughout the growing season. Narrowleaf willow may continue to flower sporadically through the growing season following a peak flowering period in May. Willows demonstrate a strong thermal control over flowering, which occurs in response to heat pulses and may be delayed by cold spells.
Narrowleaf willow seeds are generally released during a 1- to 2-month period from mid-May to mid-July; however, seed release may continue through October. Seed dispersal may correspond to low water levels, which may be important for reducing the number of seeds washed away and allowing seeds to germinate when soils are moist but not inundated.
Narrowleaf willow is winter deciduous.
Cercis orbiculata (aka: California redbud, Western redbud, Arizona redbud, Judas tree, Cercis occidentalis)
Salix lucida (aka: Shining willow, Greenleaf willow, Tail-leaf willow, Whiplash willow, Pacific willow, Lance-leaf willow, Longleaf willow, Red willow, Western shining willow)
Salix lutea (aka: Yellow willow)
Salix scouleriana (aka: Scouler's willow, Upland willow)
Prunus pumila (aka: Sandcherry, Western sandcherry, Eastern sandcherry, Great Lakes sandcherry)
Prunus emarginata (aka: Bitter cherry)
Salix bebbiana (aka: Bebb willow, Beak willow, Beaked willow, Long-beaked willow, Diamond willow, Chaton, Petit Minou, Smooth Bebb willow)
Ajuga reptans (aka: Bugle, Blue bugle, Bugleherb, Bugleweed, Carpetweed, Carpet bugleweed, Common bugle, St. Lawrence plant)
Astragalus (aka: Milkvetch, Locoweed, Goat's-thorn)
Robinia pseudoacacia (aka: Black locust, False acacia, Yellow locust, White locust, Green locust, Post locust, Falsa acacia, Robinia)
Salix boothii (aka: Booth's willow)
Salix amygdaloides (aka: Peachleaf willow, Peach leaf willow)
Rhus glabra (aka: Smooth sumac, Common sumac, Rocky Mountain sumac, Red sumac, Western sumac, White sumac)
Salix monticola (aka: Park willow, Cherry willow, Mountain willow, Serviceberry willow, White willow)
Rhamnus cathartica (aka: Common buckthorn, European buckthorn, Dahurian buckthorn)
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)
Allium schoenoprasum (aka: Chives)
Sinapis arvensis (aka: Charlock mustard, California rape, Charlock, Corn mustard, Canola, Kaber mustard, Rapeseed mustard)
Gleditsia triacanthos (aka: Honey locust, Honey shucks locust, Common honeylocust, Sweet bean locust)
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)
Prunus virginiana (aka: Chokecherry, Western chokecherry, Common chokecherry, Black chokecherry)
Salix glauca (aka: Grayleaf willow, Gray willow, Gray-leaved willow)
Amorpha fruticosa (aka: Desert false indigo, False indigo-bush, Bastard indigobush, Indigo Bush)
Rubus parviflorus (aka: Thimbleberry, Western thimbleberry)
Salix brachycarpa (aka: Shortfruit willow, Barren-ground willow, Small-fruit sand dune willow, Small-fruit willow)
Salix geyeriana (aka: Geyer willow, Silver willow)
Salix planifolia (aka: Diamondleaf willow, Planeleaf willow)
Rubus armeniacus (aka: Himalayan blackberry, Rubus discolor, Rubus procerus)
Brassica rapa (aka: Field mustard, Common mustard, Wild mustard, Wild turnip, Forage turnip, Wild rutabaga, Birdsrape mustard, Rape mustard)
Echium vulgare (aka: Viper's bugloss, Blueweed, Blue thistle)
Cucumis sativus (aka: Cucumber, Cetriolo, Gherkin)
Cucumis melo (aka: Cantaloupe, Rockmelon, Sweet melon, Spanspek, Honeydew melon, Honeymelon, Crenshaw, Casaba)
Citrullus lanatus (aka: Watermelon)
Borago officinalis (aka: Borage, Starflower, Common borage, Cool-tankard, Tailwort)