American
elm, Ulmus americana L., was the most popular street
tree due to a long trunk and vase shaped form that resulted in the branches
virtually forming a Gothic arch over the street.This over use also made Dutch elm disease
that much more devastating.A few
resistant trees have been found, perhaps 0.02% of those in existence before the
disease got introduced, but these cultivars, which are now available,should never be planted exclusively or even
close enough together for the roots to intertwine since that was one of the
main methods through which the disease spread.All our elms are susceptible to Dutch elm disease, but this was
especially true of American elm, which has twice the number of chromosomes as
the others thus it originated from a smaller genetic source that mostly lacked
any resistance.The Alabama state champion American elm is 97 feet tall, has a circumference of 185 inches, and an average limb spread of 82 feet.
Three other elm species
native to Alabama
are winged elm, U. alata Michx., slippery
elm, U. rubra Nutt., and September elm, U. serotina Sarg. The flowers and fruit, which is a samara, are
the most definitive keys, but they are so fleeting.The most attractive flower is on slippery elm where they are the largest and appear as pale green disk rather than just a bit of fuzz. Winged elm has the most prominent corky
wings of any elm on its twigs and the leaves are smooth and small.The Alabama state champion winged elm is 75 feet tall, 130 inches around, and has a limb spread of 70 feet. Slippery elm actually has very rough leaves
because the name slippery comes from the mucilaginous inner bark, which is used in
the herbal health industry as a laxative thus giving the name slippery an
unexpected meaning.The bark will
essentially slip off the tree if it is cut free and pulled, and I have seen
where the bark of every slippery elm within sight of a road was stripped nearly to the
top of the tree by herbalist poachers.The Alabama state champion slippery elm is 98 feet tall, 52 inches around, and has a limb spread of 87 feet. September elm blooms in September as the specific epithet, meaning late,
indicates considering how all the others bloom in the spring before the leaves open.There is not an Alabama champion September elm partially because it is easily mistaken for a small American elm when not in bloom.
A couple more native species ranging as close
as Tennessee
are cedar elm, U. crassifolia Nutt., and rock elm, U. thomasii Sarg., while Siberian elm,
U. pumila L., is considered an invasive exotic species, but fly-by-night mail
order nurseries continue to market it as well as many other invasive exotics. There is even an Alabama state champion Siberian elm that is 50 feet tall, inches 58 around, and with a limb spread of 61 feet.Meanwhile winged elm, besides being somewhat
weedy here, is considered to be an invasive exotic species in parts of Europe.
