Northern Minnesota phenology report: October 2011

In the fall of 2009 my phone began to ring and people stopped me on the street to ask about a plant they were seeing while they hunted grouse or deer. “It had gray bark and was about six to eight feet tall, but the really amazing thing was the bright red berries. What is it?”

At first I was a bit perplexed but I soon realized they were asking about northern holly. In that year the plants were covered in a bumper crop of fruit. Most years the winterberry, as it is also known, puts out a crop of berries. And about the time most hunters were going afield the migrating robins and white-throated sparrows would sweep through and eat them. In a normal fall the hunters were just too late to see the berries.

Something happened in 2009 that resulted in the berries remaining on the shrubs. It may have been sheer numbers, the bushes were loaded with fruit. It may have been a very good year for all fruits and the birds simply had more than they could eat and so ignored the holly. They are not particularly tasty, though to a bird with its diminished number of taste buds who knows how they taste? It may have been an unusually high level of saponins stored in the fruits making them inedible.

Saponins are a family of chemicals that produce a foaming action when stirred in water. They reduce the desire for browsing by making the fruit unpalatable. The fact that they readily dissolve in water and are toxic to fish has led to their use as a fish poison. There are still places in the world where people use plants containing saponins as a means of killing fish.

The northern holly has the ability to remove the saponins from its berries. In October the berries, cleansed of their protective chemicals, are pounced upon by migrating birds and eaten. The seeds pass through the gut of the birds and are released back into the woods unharmed. Since birds tend to openings within the forest the seeds are often released along trails, river banks, and roadsides. The plant likes wetter sites and will germinate when the conditions are good. For many years the only northern holly at my house was found along the lakeshore. In the past several years I have been discovering plants along my trails and even along my driveway.

After the seeds have been eaten the shrub can still be identified by the bark. It is a uniformly dark gray that suggests another name often applied to this plant, black alder. It’s not the dark bark that makes it easy to recognize, rather it is the waxy, silvery coating found on the new growth. So watch as you drive along for the nearly black shrubs with silvery shoots at the ends of the branches and come back for a look next summer to see the small red berries.

At one time, tea brewed from its bark was considered a tonic, as well as a treatment for fevers; externally, the bark was applied as a poultice to skin eruptions. The berries were taken as a cathartic and to expel intestinal worms, which is another way of saying that eating these berries will give you a case of diarrhea. While the fresh twigs with scarlet berries can be gathered for ornamental use, care should be taken that children do not graze the attractive fruit. My own experience with northern holly as a decorative cutting has taught me that they tend to drop their berries soon after they are brought indoors. I have had better luck using them as decorations outside.

John Latimer is well known throughout northern Minnesota for his phenology work. He appears weekly on KAXE radio in Grand Rapids.

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