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.
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)
Salix drummondiana (aka: Drummond's willow, Beautiful willow, Blue willow)
Salix amygdaloides (aka: Peachleaf willow, Peach leaf willow)
Salix boothii (aka: Booth's willow)
Robinia pseudoacacia (aka: Black locust, False acacia, Yellow locust, White locust, Green locust, Post locust, Falsa acacia, Robinia)
Salix lemmonii (aka: Lemmon's willow, Lemmon willow)
Salix planifolia (aka: Diamondleaf willow, Planeleaf willow)
Salix pulchra (aka: Tealeaf willow, Flatleaf willow, Flat-leaved willow, Paneleaf willow, Thin red willow)
Ajuga reptans (aka: Bugle, Blue bugle, Bugleherb, Bugleweed, Carpetweed, Carpet bugleweed, Common bugle, St. Lawrence plant)
Astragalus (aka: Milkvetch, Locoweed, Goat's-thorn)
Rubus laciniatus (aka: Cutleaf blackberry, Evergreen blackberry, Slashed blackberry)
Salix alaxensis (aka: Feltleaf willow, Alaska willow)
Salix geyeriana (aka: Geyer willow, Silver willow)
Rhus glabra (aka: Smooth sumac, Common sumac, Rocky Mountain sumac, Red sumac, Western sumac, White sumac)
Salix richardsonii (aka: Richardson's willow, Woolly willow)
Allium schoenoprasum (aka: Chives)
Brassica napus (aka: Rapeseed)
Sinapis arvensis (aka: Charlock mustard, California rape, Charlock, Corn mustard, Canola, Kaber mustard, Rapeseed mustard)
Prunus pensylvanica (aka: Pin cherry, Fire cherry, Bird cherry)
Calendula officinalis (aka: Marigold, Calendula, Pot marigold, English marigold)
Prunus virginiana (aka: Chokecherry, Western chokecherry, Common chokecherry, Black chokecherry)
Prunus serotina (aka: Black cherry, Wild black cherry, Rum cherry, Mountain black cherry, Wild cherry)