General: Basswood family (Tiliaceae). Native, large deciduous trees, the bark gray and furrowed with flat ridges. Leaves deciduous, alternate, more or less unevenly heart-shaped or the base often nearly truncate, petiolate, the blades 5-12.5 cm wide, thick and slightly leathery, with shallowly toothed margins, glabrous on both sides or with some pubescence on the lower surface. Flowers yellowish-white, 10-14 mm broad, fragrant and nectar-bearing, in drooping, 6-20-flowered clusters hanging on a stalk that diverges from near the center of an oblong, leaflike and strongly veined bract 5-10 cm long. Fruits mostly globose, 8-10 mm broad, hard and dry, indehiscent. The common name is from “bastwood,” referring to use of the inner bark, the “bast,” for rope, baskets, etc.
Variation within the species:
North American basswoods have been separated into many species (usually three or four) or treated as several varieties within only a single species. “Given the inconstancy of most vegetative and reproductive characters [of North American basswood], the ecophenic, ecotypic, and seasonal variation in vestiture, and also the probability of introgression,” trichome morphology provides the best evidence for recognizing the component taxa (see Hardin 1990).
a. Tilia americana var. americana
synonym: Tilia neglecta Spach
b. Tilia americana var. heterophylla (Vent.) Loud.
synonym: Tilia heterophylla Vent.
synonym: Tilia michauxii Nutt.
c. Tilia americana var. caroliniana (P. Mill.) Castigl.
synonym: Tilia caroliniana P. Mill.
synonym: Tilia floridana Small
The varieties of Tilia americana intergrade, but in their typical forms are separated as follows:
a. Leaves green beneath, sometimes glaucous, glabrous or sparsely hairy with simple trichomes, sometimes with a few stellate ones. var. americana
a. Leaves pale or whitish beneath from the close tomentum of dense, sessile-stellate trichomes, sometimes glabrate with age but remaining stellate-pubescent at least along the major veins. (b)
b. Young twigs tomentose or tomentose-hirsute; clusters of hairs on leaves more than 0.5 mm wide.
b. Young twigs glabrous; clusters of hairs on leaves less than 0.5 mm wide. var. heterophylla
Trees identified as Tilia neglecta may be variants of var. americana or they have been suggested to be introgressants between var. americana and var. heterophylla. Tilia floridana is often recognized as separate entity.
Distribution: Tilia americana is native to the Northern Deciduous and Great Lakes - St. Lawrence forest regions of North America. It also extends into grassland areas along river courses in Manitoba and the mid-western United States, where it forms a component of riverine gallery forests. In Canada, it is found from western New Brunswick into southern and central Québec and Ontario, extending as far west as north-western Ontario (along the U.S. border) and southern Manitoba. In the United States, the species occurs as far south as the mountainous regions of North Carolina, Tennessee, and northern Arkansas. The western limit for the species is south-central Manitoba and North Dakota, and along the Niobrara River in north-central Nebraska. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.
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