Fasciation

Welcome back to Ask a Naturalist: your own personal “Google” for information on all things natural on PEI! One of my favourite things about this series is the cool photos people send me. Today’s photo comes from Kevin Arsenault of Coleman who wondered about this strange, rather tropical looking plant he found here on the Island (Photo 1). This is an Evening Primrose (Oenothera biennis) showing a phenomenon called ‘fasciation’.

Photo 1: Fasciation in Evening Primrose (Oenothera biennis) on PEI. Photo by Kevin Arsenault of Coleman, PEI (used with permission).

I knew right away it was Evening Primrose, from the leaves and seed pods at the top of that distorted stem. (Photo 2 shows what a normal plant looks like for comparison). Although I’d never seen fasciation in this species, it’s not unusual among PEI plants. I’m betting you’ve seen it before without knowing what it was; I find it frequently in Dandelions (Taraxacum officinale, Photo 3).

Photo 2: A normal Evening Primrose for comparison. You can see these leaves and seed pods are the same as those on top of that distorted stem in Photo 1.

Fasciation is an abnormal growth pattern that most often results in thickened, ribbon-like stems. It can be a result of a genetic mutation but is more often caused by damage to the growing tip of the plant (called the meristem). Insects, bacterial or fungal infections, animal browse, mechanical injury, herbicides, and frost damage can all cause fasciation. It’s not limited to stems but can also be found in flowers and fruit, giving them a widened or doubled appearance, sometimes looking a bit like Siamese twins. (If you’ve ever had a wide, flat strawberry that looked a bit like the comb on the head of a rooster, you’ve had fasciated fruit). In some cases, horticulturists select for or induce fasciation in plants as interesting varieties for homes and gardens.

Photo 3: Fasciation is common in many plants, and you've likely seen it in Dandelions. On the left is a normal Dandelion stem, on the right a fasciated one.

While fasciation in Evening Primrose was new to me, it is a well documented phenomenon. In the early 1900s, Dutch geneticist Hugo de Vries studied the inherited form of fasciation in this genus extensively. Later research found that fasciation in Evening Primrose is most often caused by insect damage.

Fasciation typically results in many more than the usual number of flowers (you can see that from all the seed pods at the top of the plant in Photo 1). There’s an interesting account from 1916 of a fasciated Evening Primrose that had more than 1,000 flower buds on it!

I thank Kevin Arsenault for sending in his photo and allowing me to use it. Keep your eye out next summer, and I’m willing to bet you’ll find fasciation in Dandelions if not elsewhere around you!

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