Underground Storage Organs

Abstract

The vegetables for which the edible portion is an underground storage organ are commonly referred to as ‘‘root vegetables.’’ This is actually a much more morphologically diverse group than is suggested by that term (Table 1). Although the edible portion of some of these vegetables is in fact a swollen tap root [e.g., beet, Beta vulgaris L. ssp. vulgaris, carrot,Daucus carota L., jicama, Pachyrhizus erosus (L.) Urban, parsnip, Pastinaca sativa L., turnip, Brassica rapa L. Rapifera Group], even among those, more or less of the edible tissue may also be hypocotyl tissue (e.g., beet, radish, Raphanus sativus L. Radicula Group). Cassava (Manihot esculenta L.) and sweet potato [Ipomoea batatas (L.) Poir.] are storage roots. Some of these vegetables, however, are actually underground stems: potato (Solanum tuberosum L.) and yam (Dioscorea spp.) are tubers (fleshy underground stems with buds or ‘‘eyes’’ in the axil of leaf scars); horseradish [Armoracia rusticana P. Gaertn. stn. Nasturtium armonracia (L.) Fries] and ginger (Zingiber officinale Roscoe) are rhizomes (elongated, horizontal underground stems); and taro [Colocasia esculenta (L.) Schott], malanga (Xanthosoma spp.), and waterchestnut [Eleocharis dulcis (Burm.) Trin. ex Hens.] are corms (short, thick, more or less upright, underground stems). The edible portion of onion (Allium cepa L.) and garlic (Allium sativum L.) bulbs is even further removed from the root, being comprised of enlarged, fleshy leaf bases. The underground storage organs are also the most taxonomically diverse group of vegetables, representing more than a dozen different families, including both monocots and dicots (Table 2). The geographical origins of these vegetables are worldwide (Yamaguchi, 1983). The temperate-zone crops in this group (Table 1) are all best stored at near 0°C, while the tropical root crops are mostly best stored near 12–13°C (Table 3) due to their sensitivity to chilling injury (CI; see Chapter 16). Cassava is an exception among