Flower:

Hanging, branching cluster of 6 to 18 pale yellow flowers suspended from a leaf-like bract that forms in leaf axils on this year's new growth, emerging after the leaves in late spring. The leafy bract is pale yellow-green, 2 to 4 inches long, oblong-elliptic to spatula-shaped, rounded at the tip, rounded at the base, on a naked stalk or tapered to a winged stalk. The flower cluster's stalk (peduncle) is fused (adnate) on the lower half of the bract, the stalk's free portion 1½ to 2 inches long before branching into flower stems.

Flowers are ¼ to 1/3 inch across with 5 petals and 5 sepals, both spreading to ascending, the sepals boat-shaped, pale yellow to nearly white, the petals somewhat longer, more yellow especially with age, more oblong-elliptic, also boat-shaped but somewhat flatter. In the center are numerous stamens, up to 60, shorter than to about as long as the petals, in five groups around the central pistil. The innermost stamen of each group is typically modified into a petal-like staminode (sterile stamen), layered just in front of the petal. A single straight white style, longer than the petals, sits at the tip of the pale green ovary, the tip of the style with 5 tiny lobes.

Leaves and bark:

Leaves are simple, alternate, 4 to 6 inches long and about as wide, broadly egg-shaped to nearly round, the tip abruptly tapered to a sharp point, the base asymmetrical and heart-shaped or one side more angled or straight across. Edges are finely toothed. The upper surface is hairless and deep green, the lower surface pale green and hairless except for tufts of short, woolly hairs in at least some vein axils. Fall color is deep yellow with hints of orange, the edges often browning prior to leaf drop.

Young twigs and branches are slender and limber, smooth with scattered lenticels (pores), the young bark silvery gray-brown. Buds are oval to nearly round, rounded to short point at tip, typically reddish brown.

Bark is stringy, smooth and gray on branches, developing ridges and furrows on larger branches and the trunk. Trunks on larger Minnesota specimens can reach 2 to 3 feet diameter at breast height (dbh), though some eastern US specimens can reach over 5 feet. Clumps of multiple trunks from basal sprouts are common, cut stumps frequently sending up multiple stems.

Fruit:

Fruit is a round, woody nut-like berry, ¼ to 1/3 inch diameter, covered in minutes hairs and maturing from green to light gray-brown.

Notes:

American Basswood (a.k.a. American Linden) is a large forest tree found throughout most of Minnesota's rich forest areas, though most predominant in central and south eastern woodlands, and is an important member of the Maple-Basswood forests of the area. In the open it reproduces a large, dense crown, typically somewhat columnar to vaguely pyramidal. The flowers are fragrant and copious, pollinated by bees and providing for a large honey crop. The abundant seeds are an important food source for a wide range of small mammals and birds, even foxes. The bark is eaten by porcupines and squirrels, the latter sometimes stripping the stringy bark for nest construction. Deer browse heavily on young shoots, leaves and winter twigs.

American Basswood is only occasionally planted as a landscape tree. The wild form has generally been considered messy and weak wooded with a rank growth form. It is prone to heavy basal suckering (a major way it regenerates in the wild) and wind throw. There are however, now a number of horticultural cultivars available that have been selected for narrower columnar or pyramidal forms. The similar European Little-leaf Linden (Tilia cordata) is heavily planted in urban landscapes. It differs in several floral characteristics but over all it is a smaller tree with smaller leaves (2 to 4 inches long) and has been heavily selected for more tightly pyramidal forms. The native Linden is also host to a native wood boring beetle (Linden borer) and while it generally tolerates the pest quite well—its rapid growth usually out growing any injury—young trees under stress in urban environments can be seriously damaged by it.