Word of the Week: Dioecious

dioecious [ dahy-ee-shuhs ] adjective: plant species having male and female reproductive organs on different individual plants

Dioecious Ilex verticillata ‘Red Sprite’ (female) and ‘Jim Dandy’ (male) in October. Photo © Elaine Mills

The majority of plants reproduce via “perfect” flowers, meaning they are complete in themselves, having both male and female organs within the same structure or at least on the same plant (monoecious plants). There is another category, however, the dioecious plants.

Dioecious species have separate male and female plants, with the males bearing only stamens and the females having only pistils. Most of us as gardeners know that holly plants come in male and female varieties. You need at least one ‘Jim Dandy’ to pollinate your cluster of ‘Betty Jo’ or ‘Red Sprite’ Ilex verticillata (winterberry), and a ‘Jersey Knight’ or other male variety of Ilex opaca (American holly) to fertilize your ‘Jersey Princess’ or other lady hollies if you want them to bear fruit in the fall. One male plant can pollinate numerous female plants–how many depends on how closely they are planted to each other.

Different Female Cultivars of Ilex verticillata

 

Dioecious Gingko biloba (maidenhair tree) makes an excellent street tree–as long as it is male–in urban areas as it tolerates pollution and road salts and is not susceptible to pests or diseases.
Photo © Christa Watters

Dioecious plants depend on fertilization via wind, insects, bats, or birds, or even human hand pollination in some crops. Other dioecious plants you may know include Gingk0 biloba (maidenhair tree), dates, mulberries, some persimmons, kiwis, pistachios, currants, and many junipers. The gingko, a tree with a nearly 200-million-year history, provides an example of why one might want to plant only male trees, as some cities do on public streets. The fruits of the female trees, while attractive, become a malodorous nuisance when they eventually fall to the ground and begin to decompose.

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