Plant Sex

Wisconsin summers are like a tumultuous love affair. They can fluctuate from hot and steamy to cold and rainy in the course of one night. Did you know that summer love affairs are happening all around us in broad daylight? Plants everywhere are fornicating, right in front of us. Those pretty flowers in your yard aren’t just decoration. Every bee, butterfly, and insect lured to the flowers are willing pawns to help plants copulate. Even the wind creates an orgy of pollination (unfortunately for people with allergies) picking up pollen particles and distributing them to a willing recipient.

For some, plant sex is a little more complicated. The world of plant sex is broken down into two groups: monoecious and dioecious.

This article is a shortened version of Where Do Baby Plants Come From? by Mike Yanny.

Left: Montmorency Cherry | Right: Blue Muffin® Arrowwood Viburnum

Monoecious

Monoecious plants have male and female flowers and parts on the same plant. Literally it means “one house.” Think of the male and female parts living in the same house. An example of this would be Tart Cherry Trees. You only need one Montmorency Cherry Tree in your yard to get fruit. Members of the Viburnum genus, however, may have male and female parts on the same plant, but are self-infertile. They’ve got all the parts, but need to have a second participant for it to be a real party. Perhaps you have a hedge of Blue Muffin™ Arrowwood Viburnum (Viburnum dentatum ‘Blue Muffin’) and wondered why you never get the bright blue berries. It’s because the same cultivar can’t pollinate itself. You’d need to include another cultivar into the hedge or somewhere else in the yard, like Autumn Jazz™ Viburnum (Viburnum dentatum ‘Ralph Senior’) in order for them to cross-pollinate successfully.

Ilex verticillata male (left) and female (right) flower

Dioecious

Dioecious plants have only male or only female flower on an individual tree or shrub, or “two houses.” Think of them like college dorms (dioecious and dorm both start with “d” so it’s easy to remember). Ladies in one building and guys in another, before co-ed dorms existed. Hollies are a great example of this. Last month (June) I was sitting at my desk, typing an email, when our Senior Horticulturist, Mike Yanny, excitedly came in my office and said, “I figured out why we never get fruits on the group of Winterberries out front. Wanna see something cool?” Turns out when we planted a stand of native Winterberry (Ilex verticillata) years ago no one knew if they were male or female. In a group of 5 plants, you’d think at least one of them would have been female. Whether or not they have fruits isn’t even a sure way to tell because the plant may not have reached puberty yet. The surest way to tell if they are male or female is when they are in flower, a brief duration in spring. Sure enough, Mike and I were standing in a sea of boy flowers, not a girl in sight. Then he took me out to our container production area and we could clearly see our stock of #3 containers in full bloom. There were the boys with their stamens swollen with yellow pollen and the girls with their plump, green pistils. Mike lent a helping hand and plucked a boy flower from a shrub and brushed it against a girl flower. Laughing, I covered my eyes and shook my head. All that was missing was a little Barry White music in the background.