Quercus sp. (Oaks)
By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
Alabama Allergy & Asthma Center Collection Station—Birmingham, Alabama
Although we find tree pollens in significant numbers starting as early as January each year, it is not until late March and April that we see very high levels of these pollens. Tree pollen types we find in the aerospora include mulberry, birch, ash, sweetgum, pine, and others, but the major type of pollen during the peak of spring pollen season is oak. Oak pollen begins to show up in our collections in March and can continue into May. It is present in significant amounts, particularly during April. The genus to which all oaks belong is Quercus. This is a large genus with some 600 species known worldwide.Quercus belongs to the plant family Fagaceae, which also contains the genera Fagus (beech) and Castanea (chestnut).
Ecologically, oaks are the dominant tree species in most deciduous forests throughout the Southeast. Ecological dominance is based upon a species biomass, or frequency, or both. Oaks are found in all types of habitats; floodplains, sandy soils, dry rocky soils, etc. Oaks are one of the climax species in the ecological succession that we observe in southern forests. At one time oaks and chestnuts were the dominant trees in deciduous forests throughout eastern North America.
However, with the demise of the American chestnut, the oaks, hickories, maples, and a few other species are now the dominant tree flora in deciduous forests of eastern North America. Oaks are found throughout the world in temperate regions.As noted above, the genus Quercusis a large genus, with numerous species growing throughout the U.S. There are greater than 20 species of oaks native to Alabama and the Southeast. The Vascular Flora of the Carolinas lists some 29 species of oaks native to North and South Carolina. Oaks are not only major components in Southeastern forests but are often commonly found in suburban and urban residential areas.Many species get quite large, both in diameter and in height, upwards of 150 feet tall.
Oak trees are monecious, producing both male and female flowers on the same tree. The male flowers are produced in inflorescences called catkins. The catkins appear at or slightly before the appearance of leaves. Each catkin is made up of many male flowers, each of which produces thousands of pollen grains. Following release of pollen from the catkins they turn brown and fall from the trees. These catkins are often present in huge numbers at the base of oak trees and often collect in piles like small, brown snow drifts along the edges of sidewalks and around various objects. Oak trees can be pollinated by themselves (self-fertile) or by pollen from other trees of the same species (cross-fertile) to effect fertilization. Oaks are also known to produce hybrids between closely related species. The fruit of oaks is the familiar nut known as an acorn.
Quercus is an important genus of trees both ecologically and commercially. Oaks are used in furniture construction, barrel making, cork manufacture, and flooring and paneling. Oaks are important sources of firewood and their acorns are a major source of food and a staple in the diet of numerous species of wildlife. The genus Quercus is a vitally important genus of trees.
Oaks shed considerable amounts of pollen during the spring and their pollen acts as a major allergen for hay fever sufferers. It is a significant challenge for many allergy sufferers and may cause severe reactions in some. Note: pollen from oak trees tends to be more intense in the early morning hours so be aware of this trend when planning outside activities in the spring of the year. In general, you should count on a heavy pollen load during the spring of the year, and if you have tree pollen allergies, then take appropriate precautions to reduce exposure and minimize allergic reactions. As always, consult your allergist to determine the best course of action for you and your health.
Oak and birch pollen show cross-reactivity for some allergens. Since birch is known to show cross-reactivity with a variety of foods, one may experience similar cross-reactivity with oak pollen and foods. See the link below for cross-reactivity of birch pollen and foods:
Oak pollen is tricolpate (three short, wide furrows) and has an irregular verrucate (warty projections) exine. The furrows of oak pollen have distinct margins. The pollen grains appear in polar view to have a triangular shape with bulging transparent areas in three corners of thickened intine. See the photos below.
The size of oak pollen grains ranges from 25-45 microns and the grains are spheroidal to oblately flattened and are usually described as prolate (slightly elongated). The typical size of the grains we see in our collections is 28-35 microns. The abundant pollen production we observe from oaks covers a period of some 2-3 months, partly because of differences in flowering times among the various species of oaks we see in our area. A few examples of oak species in our area are shown below.
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Blackjack Oak – Leaves
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Water Oak – Leaves
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Willow Oak – Leaves
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Red Oak Pollen – Polar View
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Red Oak Pollen – Equatorial View