According to observations of naturalists and beekeepers.
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American plum is the most broadly distributed wild plum in North America. It occurs from southern Saskatchewan east to southern Quebec and southern Maine and south to Arizona and central Florida. Its core distribution extends from Minnesota east to Rhode Island and south to central Oklahoma and north-central Florida. Populations become increasingly isolated outside this core area, with extremely isolated plants in Washington. American plum is native to North America, but its native range is unclear. Its core range may approximate its distribution before European settlement. Human plantings have expanded American plum distribution; American plum is often planted outside its core range and sometimes escapes cultivation.
This plant is present in at least 48 states/provinces in this country.
Morphology of woody parts: American plum's form is usually shrubby, but it may grow as a small tree. It ranges from 3.3 to 33 feet (1-10 m) tall. It is likely to grow tallest and assume tree form in its southern distribution. American plum usually grows as a small, single-stemmed tree in southern Alabama, Georgia, and Florida. American plum trees have short, crooked trunks with stiff lateral branches that form wide, flat-topped, irregular crowns. Tree trunks may reach 12 inches (30 cm) in diameter. Crowns are spreading. The national champion tree is 18 feet (5.5 m) tall, 3.8 feet (1.1 m) in diameter, and 18 feet in spread; it grows in Fairfax County, Virginia. American plum wood is moderately heavy and hard. The bark is "moderately" thick. Some of all branches are spurred, becoming more so with age. Bottom branches typically grow low to the ground. American plum is commonly infected with a fungus that produces black swellings on the twigs. The root structure is not well known for American plum. A few researchers found American plum had shallow, spreading roots. A root-profile study of clay prairie soils in Fargo, North Dakota, found most American plum roots were in the 1st foot (0.3 m, 40% of roots) or 2nd foot (0.6 m; 33% of roots) of soil. Maximum root depth was 6 feet (2 m). A 15-year-old shrub in eastern Nebraska had roots extending 2.5 feet (0.8 m) deep. Lateral roots ranged from 2.5 to 11 feet (3 m) long.
Leaves and reproductive structures: American plum is deciduous. Leaves are narrow with sharp teeth; they are 3 to 5 inches (8-13 cm) long. Flowers and fruits grow on short spur shoots. The inflorescence is an umbel with 2 to 4 flowers. The flowers are strongly fragrant and showy, about 1 inch (2.5 cm) across. Fruits are yellow or red drupes, 0.8 to 1.3 inches (2.0-3.2 cm) in diameter. They may be solitary or in clusters. The seed is a smooth, compressed stone.
Stand structure and age class: American plum often forms thickets that are sometimes dense. Structure of American plum stands along moist areas in eastern Colorado has been described as "dense, almost impenetrable thickets" in a "dense, thorny mass". American plum thickets in Kansas are up to 35 feet (m) wide. Thickets spread from root sprouts.
American plum has a long period of winter dormancy relative to other Prunus. The flower bud scales are large enough to permit a 2- to a 3-fold expansion of primordial flowers. The flowers emerge before or with the leaves in early to mid-spring. Fruits ripen from mid- to late summer. Seeds mature from September to early October.
Rubus laciniatus (aka: Cutleaf blackberry, Evergreen blackberry, Slashed blackberry)
Acer grandidentatum (aka: Bigtooth maple, Canyon maple, Western sugar maple)
Salix monticola (aka: Park willow, Cherry willow, Mountain willow, Serviceberry willow, White willow)
Salix lutea (aka: Yellow willow)
Salix geyeriana (aka: Geyer willow, Silver willow)
Rhus glabra (aka: Smooth sumac, Common sumac, Rocky Mountain sumac, Red sumac, Western sumac, White sumac)
Allium schoenoprasum (aka: Chives)
Sinapis arvensis (aka: Charlock mustard, California rape, Charlock, Corn mustard, Canola, Kaber mustard, Rapeseed mustard)
Salix brachycarpa (aka: Shortfruit willow, Barren-ground willow, Small-fruit sand dune willow, Small-fruit willow)
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)
Echium vulgare (aka: Viper's bugloss, Blueweed, Blue thistle)
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)
Salix bebbiana (aka: Bebb willow, Beak willow, Beaked willow, Long-beaked willow, Diamond willow, Chaton, Petit Minou, Smooth Bebb willow)
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)
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)