By Nan McCarry
Crop wild relatives (CWR) are important reserves of genetic diversity for crop plants. But did you know that many of them are wild edibles and semi-domesticated plants in their own right that you can grow in your garden? The domestication process, the coevolution of plants and people that brought us our crops, is a spectrum without a specific endpoint–as we’ll see below, even feral crops that escape can become “re-domesticated.” Many crop wild relatives are themselves somewhere along that spectrum, having undergone some selection by humans, purposefully or inadvertently, over millenia. I find that growing these is a way to connect to humans’ long history of foraging, selecting, and farming.
Solanum pimpinellifolium, the red currant tomato, is becoming popular with gardeners. It’s the closest ancestor of the domesticated tomato, which originated in the Andes but became domesticated only after reaching Mesoamerica. Many other Solanum species–relatives of tomato (and potato)–grow in the Andes as well, such as the red currant tomato. The fruit is slightly smaller than a cherry tomato, and it grows like a weed with seedlings returning readily in subsequent years, to my delight. Beginning in the mid-20th century, it was a source of genes for resistance to disease, including Fusarium and Verticillium wilts. Breeding resistance into a crop often means that less spraying of chemicals to control pests is needed. This year I’m adding other wild tomato relatives into my garden: Solanum cheesmanii, which in the wild is found only in the Galapagos Islands, and Solanum peruvianum. Read more about these wild tomatoes and their importance to world agriculture.
One seed source for these wild tomato relatives is The Experimental Farm Network (EFN). EFN makes little-known crops and wild plants available to gardeners. They also improve plants, moving them along the domestication spectrum mentioned above, by selecting promising individuals and breeding them. Many of these are perennials that can replace annuals. Perennials hold great promise for regenerative agriculture, as they provide ecosystem services such as increased carbon sequestration while requiring less frequent plowing and watering.
EFN also has a citizen science consortium of hobby breeders who are growing out seeds and selecting those with desirable traits for replanting–the domestication process in action. Seed savers’ networks, of course, have been doing similar work for decades, but their work is focused more on saving heirloom varieties of crops. EFN does some of that, but also works with the wild relatives that are outside of the crop species itself. Learn more or get involved here.
To peruse EFN’s website is to find plants at all stages along the domestication spectrum. Many of their plants have undergone some selection by humans over the ages–from wildish plants, underused domesticates, heirloom crops, and a fascinating category: feral escapees from fields and gardens that get “re-domesticated.” One plant that has been domesticated and then developed feral forms, or “escaped from domestication,” is Brassica rapa, the plant that gives us turnips, bokchoi, and napa cabbage. EFN has been re-domesticating wild turnips that grow across southern New Jersey, and they call their re-domesticated crop Dietrich’s Broccoli Raab. I am planting seeds of this feral broccoli raab in the garden this year. More information about ethnobotanist Alex McAlvay’s research on ferality in Brassica rapa is available through the New York Botanic Garden website.
In my work at a native plant nursery, Watermark Woods, I find many North American trees and shrubs that are crop wild relatives. I’ve planted many of these at home, providing food for both wildlife and people. One native CWR that is easy to grow is American hazelnut (Corylus americana). Native hazelnuts provide resistance to Eastern filbert blight, a major threat to the domesticated hazelnut, which is grown widely as a crop in Oregon. Having evolved with Eastern filbert blight, the American hazelnut has natural resistance to it. Though small, native hazelnuts are tasty, if you get the right contraption to crack them. Oil can also be extracted from them for use in cooking.
American persimmon (Diospyros virginiana) is another native plant that serves both as a CWR (of the Asian persimmon you can buy in supermarkets) and a wild food in its own right. I’ve been intrigued to find a lot of variation among the fruits of the trees in my yard, even though they all came from the same bare-root stock from the state forestry department ten years ago. Some ripen early – as early as the first half of September – and are plump and orange. Others ripen into November and have purple coloration and are more shriveled. Ethnobotanist Nanci Ross suggested to me that these might represent individuals from two different ecotypes in North America.
There must be a history of selection in some of my persimmon trees with the more desirable fruit – perhaps wherever in the wild they were sourced from, there had been casual or purposeful selection for plump orange tasty fruit with fewer seeds. I wonder sometimes, when we find wild plants, if we can be certain that there hasn’t ever been selection in their past, either by indigenous Americans, or later by colonists, or even more recently, if cultivar genes have escaped into wild populations. Regarding selection by Indigenous Americans, Nanci Ross looks for “genetic signatures” and visible features indicating past selection in persimmons. There are of course many reports of Indigenous Americans using persimmon trees, and usually when a group exploits a plant resource, casual or purposeful selection takes place. This could involve planting the seeds of preferred individuals near the household; tending these by weeding or other special care; and then perhaps selecting among the offspring for preferred traits, like less bitter fruit and fewer seeds. This is what happened in the domestication process across all crops, mostly in prehistory, and it’s interesting to be connected to this coevolutionary process through trees on the landscape.
Like hazelnuts and persimmons, native Prunus species (plums and cherries) are sources of food for both humans and wildlife. North American Prunus are CWR of the many fruits and nuts in this group that were domesticated in Eurasia: cherries, plums, apricot, peach and almond. Native Prunus serve as rootstock for some of these domesticated fruit trees, and are sources of cold hardiness or disease resistance. Some that grow in my food forest are black cherry (Prunus serotina), American plum (Prunus americana), chickasaw plum (Prunus angustifolia), and chokecherry (Prunus virginiana). Foragers and permaculturalists have certainly experimented with these as well and I am looking forward to trying wild plums.
Hazelnuts, persimmons, and Prunus species are some of the genera that are the focus of the North American Fruit and Nut Tree Working Group, a nationwide collaboration of botanic gardens, gene banks, breeders, and researchers that has been working to conserve 90 native species that are crop wild relatives. Besides these three, other genera covered by this group are Carya, Castanea, Juglans, Pistacia, Asimina, Malus, and Persea.
The Virginia strawberry (Fragaria virginiana) is a tasty (if small) native fruit you can find at native plant nurseries and grow in your yard. It’s a fast spreading groundcover with sweet white flowers in the spring. It’s also a parent of the commercial strawberry! It hybridized with another American strawberry, F. chiloensis, in France in the 1700s. If you wonder why you can read of cultivated strawberries back into Roman times, it’s because there was a domesticated strawberry before this hybrid of American species eclipsed it. Don’t confuse Virginia strawberry with the pretty, but insipid, nonnative Potentilla indica, though this false strawberry is kind of a nice groundcover as well, in my opinion.
And finally, the sunflowers. Helianthus annuus is one of the few crops that was domesticated in what became the United States (learn more here). There are 52 species of sunflower in North America, and 36 of them have important traits for breeding with the domesticated sunflower (Kantar et al. 2015). For example, the puzzle sunflower (Helianthus paradoxus), which grows in the southwestern U.S., has high salinity tolerance, a trait of increasing importance due to climate change. Puzzle sunflower is ranked as “imperiled” by NatureServe, and other sunflower relatives are at risk as well, so it’s important to conserve these where they grow in the wild and in seed banks.
Across the spectrum from imperiled to weedy, we have the sunchoke (also called Jerusalem artichoke, Helianthus tuberosus), which is both a minor crop and a crop wild relative of the domesticated annual sunflower. Sunchoke is resistant to insect pests and diseases and is also tolerant of drought and salt. Sunchoke is probably too aggressive for many gardeners with smaller yards, but many other perennial native sunflowers are available in the native nursery trade in the eastern U.S. Some that I’ve brought into my garden are Helianthus angustifolius (swamp sunflower), H. decapetalus (Ten-petaled sunflower), and Helianthus divaricatus (Woodland sunflower).
These plants are enjoyable as wildlife habitat, food for us, or cheerful flowers, but it’s also intriguing to think about how their genetic diversity might hold the answer to some future agricultural challenge.
Nan McCarry was captivated by the concept of plant domestication in a geography class in college and has been thinking about it ever since. She received her master’s degree in Geography from the University of Texas at Austin, doing her thesis research in Guatemala on traditional home gardens. For some years she facilitated the sustainable landscaping series “Landscape for Life” in her community, seeking to broaden the discussion beyond native plants to consider our impact on our properties as a whole. She works at Watermark Woods Native Plants in Hamilton, Va. during the season and cultivates her 3-acre yard-to-native food forest transition.
References:
Anderson, J.E. (2019). Crop Wild Relatives of Root Vegetables in North America. In Greene, S.L. et al. 2019: North American Crop Wild Relatives, Volume 2.
Greene, S.L. et al. 2019: North American Crop Wild Relatives, Volume 2.
Hummer, Kim E. et al. (2019). North American Crop Wild Relatives of Temperate Berries (Fragaria L., Ribes L., Rubus L., and Vaccinium L.) in Greene, S.L. et al: North American Crop Wild Relatives, Volume 2.
Kantar MB, et al. (2015) Ecogeography and utility to plant breeding of the crop wild relatives of sunflower (Helianthus annuus L.). Front. Plant Sci. 6:84
McAlvay AC et al. (2021). Brassica rapa Domestication: Untangling Wild and Feral Forms and Convergence of Crop Morphotypes. Mol Biol Evol.
Revord, R. S., et al. (2020). Eastern Filbert Blight Resistance in American and Interspecific Hybrid Hazelnuts. Journal of the American Society for Horticultural Science, 145(3)
Ross, Nanci J. et al. (2014). The ecological side of an ethnobotanical coin: legacies in historically managed trees. Am J Bot. Oct;101(10)
The Tomato Genome Consortium (2012). The tomato genome sequence provides insights into fleshy fruit evolution. Nature 485.
Volk, Gayle (2019). Temperate Tree Fruits of North America: Malus Mill., Prunus L., Diospyros L., and Asimina Adans. In Greene, S.L. et al: North American Crop Wild Relatives, Volume 2.