Which came first: the tuber or the vine? A taxonomic overview of underground storage in the legumes

Authors: STAI, JACOB - IOWA STATE UNIVERSITY; VON WETTBERG, ERIC - UNIVERSITY OF VERMONT; SMYKAL, PETR - PALACKY UNIVERSITY; Cannon, Steven

Submitted to: Legume Perspectives
Publication Type: Review Article
Publication Acceptance Date: 9/21/2020
Publication Date: 11/5/2020
Citation: Stai, J.S., Von Wettberg, E.B, Smykal, P., Cannon, S.B. 2020. Which came first: the tuber or the vine? A taxonomic overview of underground storage in the legumes. Legume Perspectives. (19):5-7.

Interpretive Summary: The legume plant family is very important in agriculture and human nutrition, including food crops such as soybean, peanut, common bean, lentil, and forages such as alfalfa. This large and diverse family also includes other minor crops that are less well known, but have large potential, especially in particular environments and environmental niches. Among these minor crops are more than two dozen species that produce edible tubers. Examples include jicama (a bean relative), winged bean (widely used in Southeast Asia), and "prairie turnip" and "potato bean" (Pediomelum and Apios, respectively), which were used as wild-harvested foods by Native Americans in North America. This review article describes these edible tuber-producing legumes, and places them in an evolutionary context relative to other, better-known legume species. This work will help researchers and growers become better acquainted with these little-known crops.

Technical Abstract: Across the ~765 genera in the large and diverse legume family, there are approximately 25 genera that rely on underground storage organs (tubers and thickened roots). Many of these are edible, and have been used locally as foods - either wild-harvested or cultivated. Examples include "jicama" (Pachyrhizus erosus), "potato bean" (Apios americana), African yam bean (Sphenostylis stenocarpa), and "winged bean" (Psophocarpus tetragonolobus). Most of these tuberous legumes are found in one of two types of environmental niches: either in biomes with periodic droughts, where tubers may help survival during droughty periods; or in seasonal environments with transitional forest, scrubland, or riparian vegetation, where the tuberous species tend also to be paired with above-ground vines. In the latter case, tubers provide energy to enable rapid growth of the vines, which scramble over nearby vegetation. Kudzu (Pueraria lobata) is such an example. Some of these tuberous species have value as crops, where their capacity for energy storage can be utilized for nutrition. This review presents the phylogenetic relationships of 25 genera with underground storage roots, and discusses environmental niches and anatomical features of these species.