NC State University
Recently I have had phone calls from Extension agents and Green Industry professionals in 3 states asking about "poisonous" hollies in the landscape. I am not sure what stimulated this sudden interest but will share what I learned. Please remember, I am neither a pharmacologist nor a toxicologist and I certainly have done no human feeding or dose response studies. That sort of work seems more appropriate for the medical community than for a horticulturist.
Logically, the first place to look for answers after the website for Poisonous Plants of North Carolina (http://www.ces.ncsu.edu/depts/hort/consumer/poison/poison.htm) would be books on poisonous plants. 'Plants That Poison' by Schmutz and Hamilton states that the poisonous parts on hollies are the berries. "The berries of all species are reported to be poisonous if eaten in quantity. The toxic principle is ilicin. Although not considered very poisonous, the attractive red or black berries should be considered dangerous to small children." Symptoms listed are "Nausea, vomiting, diarrhea and stupor due to depression of the central nervous system." They also note that "These are the hollies used extensively as Christmas decorations. Indians and early settlers used the leaves to make a mild brew such as 'youpon tea'." The line drawings in this book look like Ilex cornuta.
'Common Poisonous Plants and Mushrooms of North America' by Turner and Szczawinski, gave a more thorough treatment. In the section on English holly (Ilex aquifolium) and related species, they write "Berries and leaves may cause digestive upset; berries occasional cause of poisoning in children, but not known to be fatal." They say the berries and leaves contain theobromine, a caffeine-like alkaloid listing the same toxicity symptoms as Shmutz and Hamilton. "However, fatalities from Holly are unknown, and their poisonous properties are frequently overstated. Mild doses of the leaves or berries cause stimulation of the central nervous system, whereas higher doses cause depression of the central nervous system." If large quantities of the berries have been ingested, they suggest that vomiting be induced followed by activated charcoal and a saline cathartic, excess stimulation caused by theobromine can be countered with barbiturates and benzodiazipines. Obviously, medical professionals need to be involved if treatment becomes necessary.
Turner notes that Yaupon holly, Ilex vomitoria, leaves were used to create a mild caffeine containing tea that was used as a substitute for coffee and tea by southerners in the American Civil War and notes a concentrated brew caused hallucinations and vomiting. Galle, in his massive work 'Hollies, The Genus Ilex,' writes that this concentrated brew was 'black drink', prepared for Native American ceremonial use.
The South American beverage Yerba Mate or Paraguay Tea is made from the holly Ilex paraguariensis var. paraguariensis and is still widely used as a stimulating tea. It contains caffeine. The drink is made from the dried fermented foliage with many cultivars grown in South America. The process reminds me of what is done to Camellia sinensis to make the popular black teas we can purchase in our grocery stores. To my knowledge, Paraguay tea is not an important landscape plant anywhere in the United States.
When I checked for specific toxicity references to our common landscape hollies, I found almost nothing. For the native evergreen species besides Yaupon holly, Ilex opaca, I. cassine, I. glabra and deciduous species, I. decidua and I. verticillata already mentioned, I found that the leaves of I. cassine were sometimes used by Native Americans like the leaves of I. vomitoria to make black drink. There were no other references uncovered that indicated these native species have any toxicity at all. In my more southern days, my favorite honey was gallberry honey which occurs when honeybees are foraging on the flowers of I. glabra and I. coriacea. Despite regular consumption, no toxicity was ever noted.
For the evergreen Chinese species, I. cornuta, there were medical references. The Chinese use I. cornuta in a variety of ways. The bark, leaves and fruit are used in herbal medicine for their general tonic value as well as for diseases of the kidney. Galle writes that seed oil is used in China for soap manufacturing plus a dye and gum are extracted from the bark. This very common landscape species, despite being pictured in a poisonous plants book, appears not to be toxic.
The evergreen Japanese hollies, Ilex crenata, seem to be everywhere in commercial landscapes in USDA hardiness zones 6-8. I. pernyi and I. rugosa are also evergreen hollies native to the orient which are increasingly finding their way into landscapes as selections of the species I. pernyi or as hybrids such as I. x meserveae, the blue hollies, with Ilex rugosa as a parent. The oriental cousin to our native deciduous winterberry hollies, I. serrata, has also made it into gardens as cultivars and hybrids, perhaps the most famous of which is 'Sparkleberry' from the U. S. National Arboretum. No references to medicinal uses or toxicity were found for any of these holly species.
Therefore, it seems that rather than panicing if holly berries or leaves are ingested, we should remember that Turner wrote "fatalities are unknown and their poisonous properties are frequently overstated." In my search only a few species were listed as having medicinal uses. So, if your callers can not watch what their toddlers are eating they probably have much more to fear from common beverages, condiments and household chemicals than from hollies in their landscape.
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