American Basswood

Scientific Name: Tilia americana
— pronounced TIL-ee-uh a-mer-ih-KAY-nah
— Tilia, Latin for linden tree. 
Mallow Family (Malvaceae): over 4,000 species, including hollyhock, hibiscus, cotton, okra, cacao tree
Other Common Names:  American Linden 

all photos by Peter Dziuk at minnesotawildflowers.info

​Young American Basswoods have smooth grey-green bark; adult trees, gray-brown with long, shallow furrows.
The leaves are arranged alternately.  They are heart-shaped, with an unequal base and serrated margins.
The flowers are fragrant and creamy yellow, in clusters suspended from a long leafy "wing," blooming in late spring.
The fruit is a round nut-like berry, 1/4 to 1/3 inch in diameter, usually containing just one seed.  At maturity it is covered with grayish-brown wooly hairs.

flowers and developing fruit

Photos and more ID help:  VA Tech dendrology sheet
Interesting Facts:

• American Basswood grows up to 80 feet tall and two to three feet in diameter.   At about 15 years of age, a Basswood tree starts producing its seeds, which are a good food source for small mammals and birds.
• Typically, Basswoods live about 100 years, but some live 140 to 200 years.
• According to Lee E. Frelich, Basswoods are susceptible to invasion by fungi, which hollow out the trunk until the it buckles and collapses; this is the common cause of death for the "above-ground" tree. The stump then produces sprouts that grow quickly to adulthood, and the cycle may repeat; so it’s possible that a genetically-defined "individual" Basswood may live for centuries. 
• Meantime the decaying wood in the standing tree welcomes cavity-nesting animals, including wood duck, pileated woodpecker, and numerous smaller birds and small mammals.
• Basswood flowers are pollinated by as many as 60 species of insects, including bees and flies in the daytime and moths at night.

The "bass" in Basswood comes from the word "bast," which refers to strong woody fibers used for cordage — in this species, the fibrous, tough inner bark.