Rubbish Heap Hypothesis

The wild mustards have been flowering profusely along the roads in my area recently. Many are considered weeds. There are several species flowering now, most with yellow or white flowers. Some of you may have noticed an escaped ornamental mustard with blue flowers in road ditches and waste places across much of the state. That is probably dame’s rocket.

Mustards are quite easy to identify because they are annual or perennial herbs with alternate leaves and flowers with four petals that resemble the form of a cross. Historically the mustard family was known as the Cruciferae (a reference to the cross) although the family is now called the Brassicaceae.

It may seem strange that this family with so many weeds also contains several garden and agricultural crops. Cabbage, cauliflower, kohlrabi, Brussels sprouts, broccoli, and kale are all different varieties of the same mustard species (Brassica oleracea). Plus there are other species, including radish, canola, rape, and of course black mustard.

A large number of crops and weeds in any particular plant family should not surprise us. That is because the ancestors of many of our modern crops were weedy annuals growing in the dumps, kitchen middens, and other disturbed areas in and around early settlements. It is what botanists call the Rubbish-Heap Hypothesis. Most of our domesticated crops are essentially domesticated weeds.

Just consider it for a moment. Most all our garden crops as well as our more mainstream agricultural crops are annuals. Annual plants generally grow in disturbed areas, grow quickly, and produce a lot of seeds. They are weedy species. But those same plants have the characteristics that can make for a good crop. Over many generations we have selected or chosen those plants that produced more, bigger, and more nutritious seeds. We also selected those plants that were perhaps a little more disease and drought resistant. Consider all this the next time you see all those weeds along the roads, in the fields, or in your garden. Someday, long after we are gone, they may be important crops!

Chuck Lura
Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.