Oleacea – Ligustrum sp.
By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
Alabama Allergy & Asthma Center Collection Station – Birmingham, Alabama
If you have been reading my recent blogs, you are aware that I am writing a series on species of plants that are principally wind pollinated and which produce pollen grains that act as allergens. This blog will focus on one of the genera that belongs to the olive family of plants, a group of plants which are known to produce pollen that is often a significant cause of hay fever and asthma. This blog will deal focus on the genus Ligustrum, common name privet, while previous ones dealt with the olive, Olea europaea, and ash trees, genus Fraxinus.
Oleaceae (olive family) is a family of plants native to temperate and tropical regions of the northern hemisphere. There are 25 genera and some 700 species in this family. The best-known members of this family are olive, ash, lilac, privet, Jasminum and Forsythia. The members of this family are trees, shrubs, and climbers, some of which are important economically. The olive (Olea europaea) is important for the fruit it produces which is the source of olive oil. The ashes (Fraxinus) are valuable as a source of lumber and because of the toughness of the wood is often used for manufacture of tool handles and baseball bats. The shrubs Forsythia, lilac, privet, fringe tree, and jasmine are valued for use as ornamentals in gardens and landscaping.
There are approximately 50 species of Ligustrum and they typically grow as erect, deciduous or evergreen shrubs. Occasionally plants may grow to reach heights of small to medium-sized trees. The genus is native to Europe, north Africa, and Asia. It has become naturalized in Australia and North America. Privet is a fast-growing shrub which can be grown as a very thick hedge. The leaves are semi-evergreen and 1-2.5 inches long. They are borne in an opposite arrangement on twigs. Its dense foliage and typical height of 4-8 feet, make it an effective privacy hedge during the summer. Privet grows more quickly than boxwood shrubs and tolerate heavy pruning and shaping, hence making it an attractive planting as a hedge. Privet also tolerates urban pollution and is somewhat salt-tolerant. Ligustrum tolerates a variety of soil types, and competes extremely well with native species. In fact, its ability to outcompete native vegetation has led to privet becoming a significant invasive species in many parts of the United States (particularly the South and Southeast) and Australia. It produces small, white flowers in the late spring. The flowers are produced in compact terminal clusters (panicles). The flowers have a musty, disagreeable odor that is attractive to insects, the principal pollinator of privet flowers. However, if the pollen is not taken away by insects, it can be dispersed by the wind. The flowers are succeeded by small blue to black berries (botanically these are drupes) which are most obvious during the fall when some or all of the leaves fall from the plants. Each plant will produce large numbers of berries which are a source of food for a variety of species of wildlife. Birds often feed on these berries and serve to disperse the seeds present in these fruits by way of their droppings.
Chinese privet leaves and bark are used in traditional herbal medicine for treatment of various gastrointestinal problems and for chapped lips, sore mouths, and throats. The tea produced from privet leaves is bitter and has been used to improve appetite and digestion in some individuals. Some species of Ligustrum produce fruits that are mildly toxic to humans and in general it is a good idea to avoid eating the fruits of any of the species of privet. The ability of birds or other wildlife to consume privet fruits without suffering harm should not be interpreted to mean that they are safe for humans to eat.
Ligustrum pollen shares common allergens with olive tree pollen and may be lead to cross-reaction between olive tree pollen and privet pollen. The pollen is allergenic although it is not a significant cause of hay fever or asthma because the pollen is typically not airborne; most pollination is the result of insect activity. Problems occasionally arise if the plants are present in large numbers and allowed to flower near where people are living or where people are involved in some type of outdoor activity. Conclusion, consider privet pollen a potential causative agent of local allergy in areas where it extensively present in the environment.
Pictures below are of Chinese Privet, Ligustrum sinense.
Privet growing as a small tree
Privet leaves with young fruits
Privet growing as a shrub
Privet leaves and flowers