Crop Wild Relatives of the United States

a blog about their conservation and use

National Inventory

Development of a national inventory of CWR and useful plant species

We have compiled a national inventory1 of taxa representing crop wild relatives (CWR) of the world’s crops, and wild species directly used for food, fiber, forage, medicinal, and other purposes. We defined CWR following Maxted (2006)2 (essentially, close relatives of crops, as defined by belonging to the primary or secondary genepools), but broadened our list to include species within the tertiary genepool, as a number of crops have increasingly benefited from traits introgressed from distant genepools, e.g. pigeonpea3 and beet4, and as these species are also useful for phylogenetics, evolution, and other research5. In general, our method included within the inventory any species within the same genus as the associated crops.

Cucurbita foetidissima

The inventory was created from data sources including the Germplasm Resources Information Network (GRIN) World Economic Plants Database6 based on Wiersema and Leon (1999)7, completed volumes of the Flora of North America8, McGuffin (2000)9 (for herbs and medicinal species), and the Native Seed Network Database10 (for restoration species). Both native and non-native taxa were included. USDA National Plant Germplasm System (NPGS) curators, members of the NPGS Crop Germplasm Committees, and USDA Agricultural Research Service (ARS) crop experts then contributed revisions. The national inventory currently contains 4,600 taxa.

In order to prioritize species within the national inventory for further conservation analyses, we first collated a list of the most important crops around the world, and then identified the crop wild relatives distributed in the U.S. that are related to such crops.


1Khoury CK, Greene S, Wiersema J, Maxted N, Jarvis A, and Struik P (2013) An Inventory of Crop Wild Relatives of the United States. Crop Sci. 53(4): 1496.
2Maxted N, Ford-Lloyd BV, Jury SL, Kell SP and Scholten MA (2006) Towards a definition of a crop wild relative. Biodiversity and Conservation 15(8): 2673–2685.
3Mallikarjuna N, Deepak J, and Prabhakar R (2006) Introgression of Cajanus platycarpus genome into cultivated pigeonpea, C. cajan. Euphytica 149 (1-2) (June): 161-167.
4Frese L, Desprez B, and Ziegler D (2001) Potential of genetic resources and breeding strategies for base-broadening in Beta. In Broadening the genetic base of crop production, eds. Cooper HD, Spillane C, and Hodgkin T, CABI, Wallingford, pp.295-309.
5Debouck DG (2010) International Center for Tropical Agriculture, Colombia. personal communication.
6USDA ARS National Genetic Resources Program, Germplasm Resources Information Network (GRIN), World Economic Plant Database.
7Wiersema J and Leon B (1999) World Economic Plants: A Standard Reference. Boca Raton (FL): CRC Press LLC.
8Flora of North America Association (2008) Flora of North America.
9McGuffin M and American Herbal Products Association (2000) Herbs of commerce. 2nd ed. [S.l.]: American Herbal Products Association.
10Native Seed Network (2010) Native Seed Network Database.
Photo: buffalo gourd (Cucurbita foetidissima Kunth) by C. K. Khoury