American Basswood is a large long-lived native deciduous tree, growing 60 to 100 feet in height and 2 to 4 feet in diameter with a dense rounded crown with lower branches usually drooping. Trees in an open area may have a more rounded, conical crown. There are frequently several trunks.
Bark is smooth and thin when young, gray-green turning dark gray with age, becoming thick and furrowed into narrow scaly flat-topped ridges with characteristic horizontal cracks. The inner bark is fibrous and very useful.
Twigs are green initially turning reddish by winter, somewhat zigzag in shape, hairless with plump buds with an acute tip and covered with at least 2 visible reddish scales. One side of the bud bulges out.
Leaves are broadly ovate to rounded, 3 to 6 inches long and almost as wide, long-pointed at the tip, with coarsely saw-toothed margins and a base that is a bit heart shaped but unequal symmetrically. The vein pattern is pinnate, the upper surface is shiny dark green, the underside is paler and nearly hairless except for hair in the axils of the veins. Newly formed leaves have at their base a thick bract that withers away with the aging of the leaf. The leaf is quite soft, earning the nick-name "nature's toilet paper". Fall color is yellow to brown.
Flowers: The flowers are bisexual, yellowish-white, 1/2 to 5/8 inch wide and occur in drooping clusters (cymes) of 6 to 20 flowers, the clusters being 1 to 3 inches wide, which rise from near the axils of the leaves. The cluster hangs from a long stalk, the bottom half of which is attached to a yellowish-green oblong, curving, veined floral bract, about 1/2 inch wide and narrowed at its base. Each small flower has 5 cream-ish color petals that are slightly longer than the 5 sepals of similar color; numerous stamens grouped into 5 clusters, with yellow anthers which turn darker at pollen maturity. There is a multi-celled ovary with a single white style which has 5 lobes at the tip. Both the ovary and the base of the style have whitish hairs. Flowers are fragrant, nectar bearing, insect pollinated and develop relatively late - several weeks after leafout.
Fruit: Flowers mature to a 1/4 inch round hard nutlet which is covered by gray-brown hair and contains, usually, just 1 seed. These mature in the fall and can persist on the tree into the winter. The curving bract to which the flower cluster is attached can act like a wing for wind dispersion a short distance. Trees must be about 15 years old before they bear fruit. The hard seed coat provides several years of seed dormancy.
Habitat: Basswood has large lateral root system and usually not a taproot. Seedlings do well in shade but development requires full to partial sunlight. Moist rich soils are best. Basswood sprouts vigorously from stumps, often developing into new multi-trunk full size trees. This is a good shade and ornamental tree and the nursery trade has developed several cultivars for landscape use but they as not considered as long-lived as the original species.
Names: The genus Tilia is the Latin name for the Linden or Lime tree. The species americana, refers to North America, to distinguish the species from the European species. The author name for the plant classification - 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: There are several varieties of the tree that are recognized from geographical differences. Close relatives would be in the Lindens.
Above: - Two different shapes of the tree. 1st photo - a younger tree in an open space. 2nd photo - an old tree with double trunk in a confined space. 3rd photo - Prior season twig - the reddish twig color dissipates with age. Note the large bud, bulging to one side, with two apparent bud scales
Below - Bark: 1st photo - bark of a younger tree. 2nd photo - bark of a main branch. 3rd photo - bark of an older tree with lichen growing on it.
Below: Buds opening in Spring.
Flowers: Above and below: Note the sepals are a bit shorter than the petals, yellow anthers on the stamens and a single white style. The example below shows the lobes at the tip of the style. 2nd photo below shows the long floral bract and how the lower half of the flower cluster stem attaches to the lower half of the bract.
Below: 1st photo - A cluster of formed nutlets. Note the floral bract above. 2nd photo - A pair of mature hard nutlets which each contain a single dark brown seed.
Below: Leaves are almost as wide as long, with a pinnate vein pattern, unequal heart-shaped base and coarse sawtooth margins.
Below: Drawing by Pierre-Joseph Redouté, from The North American Sylva by Francois Michaux and Thomas Nuttall.
Notes: American Basswood is indigenous to the Garden. Eloise Butler catalogued it on April 29, 1907. Garden Curator Susan Wilkins added additional plants in 2008 and 2015. In North America it is the northernmost Basswood species ranging from Saskatchewan to the east coast in Canada excepting the Maritime Provinces and in the US from the central plains east to the coast, south as far as Oklahoma, Kentucky and South Carolina. Within Minnesota it is found in all but 22 counties, those exceptions being mostly in the SW - the old prairie area. It is the only Tilia species native to Minnesota.
Uses: Basswood wood is soft, light and useful for utility things like boxes, veneer, wood carving, toys and mainly for pulpwood. It decays easily and is not suitable for exterior applications. There are numerous reports of the fibrous inner bark being used for making strings, twine, nets, etc, by the Native Community. Francois Michaux confirms this in Volume 3 of his North American Sylva. (Ref.#26d) He states "The trunk is covered with a very thick bark; the cellular tissue, separated from the epidermis and macerated in water, is formed into ropes, which are used only in the country. In Europe they are sold for certain purposes in the cities, particularly for well-cords."
Fiber: Native peoples made twine from the inner bark fibers. Frances Densmore’s extensive study in the 1920s of plant use by the Minnesota Chippewa, (Ref. #5) particularly the White Earth group, detailed medicinal, food and craft uses of various plants. Twine is a multi-purpose article and it was made in this manner: Bark was cut from the Basswood tree in long strips and soaked in the lake water for several days. Then the soft useful inner bark could be separated from the tough outer bark into strips less than an inch wide and stored in coils for future use. The strip could be used full width if toughness and strength was needed, or separated into fine threads as soft and fine as cotton. When twine was needed, the fibers could be twisted to make twine. If a really tough strip was required, the fiber could be boiled.
Tea and Chocolate: The fragrant flowers have been used to make a soft flavorful tea and from the nectar bees produce the palest and most complex honey, with floral scents and notes of mint. The most interesting use however, comes from Europe where it was discovered by a French chemist in the 18th century that grinding the unripe nutlets of the European species with the dried flowers produced a substance with the aroma and taste of chocolate. This was confirmed by others but production did not occur because the product did not keep. Several have suggested that use of the American species would have resulted in a more keep-able product. See Fernald (Ref. #6) for more details. Recipes for this chocolate can be found on the internet by looking up the French chemist "Missa".
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"