American basswood

Great Plains

Midwest

FACU - Facultative upland

Northcentral & Northeast

FACU - Facultative upland

Native

Common

Moist to moderate moisture. Deciduous forests, alluvial plains not subject to repeated long-duration spring flooding. Often on moist, northeast-facing slopes.

Early July to early August

Greenish-yellow to white

50′ to 70′

This is a fast-growing, deciduous, hardwood tree. It rises on a single or often two or more stems, usually from suckers. In Minnesota mature trees are usually 50′ to 70′ tall and up to 36″ in diameter at breast height. Large individuals can reach 90′ in height. It is a long-lived tree, often surviving over 200 years.

The trunk is straight and is distinct into the upper part of the crown. There are often suckers growing at the base of the trunk. The crown is relatively small, symmetrical, smooth, and rounded. The branches are ascending and arching, with tips ascending. When struck lightly with the handle of a tool the trunk sounds hollow.

The bark on young trees is thin, smooth, and light gray. As it ages it becomes moderately thick, dark grayish-brown, with deep, V-shaped fissures and long, narrow, flat-topped, scaly, vertical ridges that are transversely divided into short blocks.

The twigs are moderately stout, zigzagged, and hairless. They are deep green in the first season, becoming deep red in the winter, and light grayish-brown in the second year.

The buds are green or red, 3 ⁄16″ to ¼″ long, oval, shiny, and hairless. They have 2 bud scales. There are no terminal buds. The leaf scars are half-oval with 5 to 10 bundle scars.

The leaves are deciduous, alternate, and not lobed or divided (simple). They are thin, broadly egg-shaped to nearly circular, 3″ to 6″ long and 2″ to 5″ wide. They are on 1″ to 2¾″ long leaf stalks. The blades taper abruptly at the tip to a sharp point with concave sides along the tip. They are heart-shaped and unequal at the base. The upper surface is dark green and hairless. The lower surface is paler green and hairless except for tufts of brown hairs in the leaf axils. The margins are coarsely toothed, the teeth sharp and forward pointing with elongated tips. In autumn they turn yellow to orange. Leaves on suckers are often much larger.

Flowers have both male and female parts. They appear after the leaves in early July to early August and last two weeks. They are borne in loose, many-branched clusters (cymes) of 4 to 40 flowers drooping from leaf axils. The clusters are on a stalk that is fused for about half its length to a to a leaf-like bract. The bract is yellowish, spatula shaped, 2″ to 4″ long, and gracefully curved.

The individual flowers have 5 hairy sepals, 5 greenish-yellow to white petals, and about 60 stamens, and are fragrant.

The fruit is a light brown or gray, spherical, hard, nut-like drupe, ¼″ to ⅜″ in diameter. It is finely hairy and has a sharp-pointed tip. It matures mid-August to mid-September.

When the basswood seed sprouts the seed leaves, the first pair of leaves to appear above ground (cotyledon leaves), are palmately five-lobed.

Littleleaf linden (Tilia cordata) leaves are much smaller, 1½″ to 2½″ long. It is a European species often planted on city boulevards. It is not naturalized and is not found in the wild.

Linden leaf gall mite (Eriophyes tiliae) creates raised, finger-like galls in the upper leaf surface.

Linden wart gall midge (Contarinia verrucicola) creates warty galls, each one raised on both the upper and lower surfaces.

The champion American basswood in Minnesota is on city property in Oronoco, in Olmstead County. In 2012 it was measured at 91′ tall and 192″ in circumference (61″ in diameter).

Basswood foliage, Freeborn County, MN, August 2017

Basswood nutlets, Freeborn County, MN, August 2017

Larger leaf on a basswood sprout, Freeborn Co., MN, May 2017

Freshly fallen American Linden near MN/IA border

Basswood, Rice County, MN, October 2016

Tree

Leaves

Bark

Cotyledon Leaves

Location: Freeborn County, MN

Basswood nutlets

Location: Freeborn Co., MN

Larger leaf on a basswood sprout

Location: near MN/IA border

Freshly fallen American Linden

Location: Rice County, MN