Getting to Know Our Local Pollen: Elms

Share on FacebookTweet about this on TwitterEmail this to someonePrint this page

Ulmus sp.
(Elms)

By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
Alabama Allergy & Asthma Center Collection Station—Birmingham, Alabama

 

As pointed out in an earlier blog, the first of the tree pollens that we see in northern Alabama is cedar, a gymnosperm. Gymnosperms are trees that do not produce flowers; pollen is produced in structures called pollen or male cones.

 

The first angiosperm (a plant that produces flowers) pollen that we find in large numbers in our collections is elm. Elm trees begin to flower in late January to early February and will produce pollen in our area throughout the month of February and most of March. We often find elm pollen in our collections in low numbers even in early April. There are several elm species native to northern Alabama but the most prevalent species is winged elm, Ulmus alata. Other species of elm that flower in the late winter/early spring timeframe are U. americana (American elm) and U. rubra (slippery elm or red elm). One species of elm which is native to Alabama flowers in the fall (September and October), and is appropriately called September elm, U. serotina. One additional species of elm that we find frequently in some areas of Alabama and which flowers in the fall is Chinese elm, U. parvifolia. This species is not native to the U.S. but is widely planted in many urban areas as a street tree and is also used for a variety of other landscape purposes.

 

American elm was once a common species found throughout the eastern U.S. Its normal habitat is bottomland, floodplains, and stream banks, but it can also be found on hillsides and well-drained soils at higher elevations. American elms were widely planted as shade trees around homes and in urban areas along streets prior to the introduction of Dutch Elm Disease which led to a significant decline in the number of these trees. American elms can reach over one hundred feet in height and can live several hundred years in areas unaffected by Dutch Elm Disease.

 

 

As mentioned above, winged elm is the most common species of elm found in Alabama. Winged elm is most commonly found growing on drier, upland, or rocky soils but can occasionally be found in wet areas and along streams. Winged elms also can invade formerly cultivated fields, and is a normal though minor component of deciduous forests throughout Alabama and the Southeast. This species is easy to recognize in the field because of the “wings” that are present on twigs that are two years or older. These wings are flattened, corky ridges that form on two sides of the twig. The only other native tree species that form these corky ridges on twigs are September elm and sweetgum, both of which are easily distinguished from winged elm through leaf size and shape, or leaf bud size, shape, and whether the buds are smooth or fringed.

 

Elms produce incomplete flowers that are perfect. That is, flowers contain both male and female reproductive structures, but flowers lack petals. The flowers are produced prior to leaf formation which permits elm pollen to readily get into the air and become part of the aerospora. Flowers have four to nine stamens and are produced in clusters at the tips of short spur twigs with 4-10 flowers per cluster. Following pollination, the flowers produce flatten fruits called samaras. (Note: the samaras of elms have been used as food and are edible either raw or cooked when young. They have a slightly “nutty” flavor. No recommendation is being made by this author for the use of elm fruits as a food source in your diet.)

 

Elm pollen is quite distinctive when viewed under a microscope at 400X. The pollen has 5-6 pores that are irregularly spaced. It is medium in size, 25-36 microns, with rugulate sculpturing on the surface.

 

 

By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
Alabama Allergy & Asthma Center Collection Station—Birmingham, Alabama

 

Note: This is one of a series of blogs that describes some of the common species of plants that produce pollen in our area that are known to serve as allergens. It is a good idea to know what the plants look like that produce pollen that act as allergens and try to avoid having them around where you live if possible. You should also stay alert to when plant pollens to which you are allergic are being produced in the area where you live.