Turnip
The turnip (Brassica rapa subsp. rapa) is a cool-season root vegetable in the Brassicaceae family, cultivated primarily for its enlarged, crisp white taproot, which is typically rounded and may have a purple-tinged crown, as well as its tender, fuzzy green leaves that resemble mustard greens.[1][2] It is a biennial plant grown as an annual, reaching 12–14 inches in height with light green, sparsely pubescent leaves and small yellow flowers in its second year, thriving in moderately deep, fertile, slightly acidic soils (pH around 6.0) and tolerating frost but bolting in summer heat.[2][3] Originating from wild forms in the Caucasus region, turnips were likely domesticated by humans near the Hindu Kush mountains in present-day Afghanistan between 3,500 and 6,000 years ago, initially selected for their starchy taproots before spreading westward to Europe and eastward to Asia, where further breeding produced diverse cultivars including leafy greens like bok choy and oilseed varieties.[4] In Europe, turnips have been consumed as a vegetable since prehistoric times and used as livestock fodder for over 600 years, with U.S. agricultural research in the early 1900s emphasizing their value for ruminant nutrition.[2] Turnips are nutrient-dense, providing high levels of dietary fiber, vitamins C and B6, folic acid, calcium, potassium, and other micronutrients like vitamin A, thiamine, niacin, magnesium, and copper, while also containing glucosinolates that may offer protective effects against certain cancers.[1][3] They are versatile in cuisine, with young roots and greens eaten raw in salads, cooked in soups or stews, or used as microgreens, and their tops offering 20–25% crude protein for forage; best harvested when roots are 2–3 inches in diameter after 40–60 days of growth.[1][2] Cultivation occurs worldwide in temperate regions, planted in fall or spring in rows spaced 18 inches apart, requiring full sun and well-drained soil, with varieties like 'Purple Top White Globe' prized for both roots and tops.[1][3]Taxonomy and Nomenclature
Etymology
The English word "turnip" first appeared around 1530 as "turnep" or "turnepe," likely a compound formed from "turn," referring to the rounded shape of the root as if turned on a lathe, and "nepe" or "nep," an earlier term for the vegetable derived from Latin nāpus, meaning turnip or rape.[5][6] This etymology is supported by Nathan Bailey's An Universal Etymological English Dictionary (1721), which explains "turn" as distinguishing the round napus from the generally long napi.[7] Linguistically, the root traces back further to Old English nǣp or nēp (Anglian dialect), borrowed directly from Latin nāpus, a term used by classical authors like Pliny the Elder for the plant.[8] By Middle English, this evolved into "nepe," but the full compound "turnip" emerged to specify the bulbous variety. The Latin nāpus also influenced Romance languages, such as French navet, a diminutive of Old French nef or navet, entering English usage indirectly through Norman influences after the 1066 Conquest.[9] In Scottish and northern English dialects, "neep" persists as a synonym for turnip, preserving the older form.[8] Related terms highlight distinctions within the Brassica genus. The turnip (Brassica rapa subsp. rapa) contrasts with the "rutabaga," a larger relative (Brassica napus), whose name derives from Swedish dialectal rotabagge (circa 1799 in English), combining rot ("root," from Proto-Indo-European wrād-, meaning branch or root) and bagge ("bag" or "lump," akin to "bag").[10] This Swedish term, meaning "root bag" or "baggy root," reflects the vegetable's swollen form and underscores etymological divergence from the turnip's Latin-derived name, avoiding confusion with other Brassica species like rape or cabbage.Taxonomy and Classification
The turnip belongs to the family Brassicaceae, genus Brassica, species Brassica rapa L., and specifically the subspecies Brassica rapa subsp. rapa (Metzg.), which is cultivated primarily for its edible root. This subspecies is distinguished from others within B. rapa, such as subsp. oleifera (DC.) Metzg., which is grown for oilseed production as turnip rape. The classification reflects the plant's position in the order Brassicales and its close relation to other cruciferous vegetables.[11][12] Phylogenetically, Brassica rapa traces its origins to wild populations in Central Asia, particularly the Hindu Kush mountain region near present-day Afghanistan, where domestication began around 3,500 to 6,000 years ago through human selection for diverse traits. Genetic diversity studies reveal that wild B. rapa forms underwent independent domestication events across Eurasia, leading to convergent evolution in crop morphotypes like root, leaf, and seed types, with reduced genetic variation in cultivated lines compared to feral or wild relatives.[13][14] In the broader Brassica taxonomy, B. rapa (with its AA genome) is a key progenitor in the "triangle of U" model, which illustrates the allotetraploid origins of major crops through hybridization and genome duplication. It contributes the A genome to species such as Brassica juncea (L.) Czern. (AABB, Indian mustard) and Brassica napus L. (AACC, rapeseed), alongside B. oleracea L. (CC) and B. nigra (L.) W.D.J. Koch (BB). Subspecies variations in B. rapa—including subsp. rapa for roots, subsp. chinensis (L.) Hanelt for leafy greens like bok choy, and subsp. pekinensis (Lour.) Hanelt for Chinese cabbage—demonstrate adaptive genetic divergence driven by regional cultivation pressures.[15][14] B. rapa exhibits hybridization potential with related diploids like B. nigra, facilitating gene flow and the polyphyletic origins of allotetraploids such as B. juncea via interspecific crosses, as evidenced by chloroplast and nuclear DNA analyses. This capability underscores the genus's evolutionary plasticity but also raises concerns for gene introgression in agricultural settings.[16]Botanical Characteristics
Morphology
The turnip (Brassica rapa subsp. rapa) is a biennial herb characterized by an upright growth habit, forming a basal rosette of leaves in the first year before developing a flowering stem in the second year.[17][18] It typically reaches heights of 30–120 cm, with erect stems that are simple or branched in the upper half and may be hairless or sparsely covered in soft hairs.[18] The plant features a prominent white taproot that swells into a globular or tuberous storage organ, measuring 5–20 cm in diameter, composed of hypocotyl and root tissues with secondary growth from the vascular cambium.[19][20] The upper portion of the root often exhibits purple or red pigmentation due to anthocyanin accumulation, while the interior remains white and fleshy.[21] Leaves form a basal rosette, measuring 10–40 cm in length, with pinnately lobed or divided edges, a large central lobe, and smaller side lobes; they are glabrous or finely hairy, yellowish-green, and wavy-margined, resembling those of mustard plants but with more pronounced lobing.[17][18][20] Flowers are bright yellow, cruciform with four petals 6–13 mm long, arranged in terminal racemes, and the plant is self-incompatible, relying on insect pollination.[17][18] Fruits develop as linear siliques, 3–8 cm long and 2–4 mm wide, containing 8–15 seeds per locule for a total of 16–30 small, oval, reticulate seeds that are yellow to dark brown.[18] As a cool-season crop, the turnip completes root development in 55–60 days from sowing, with harvest occurring when the swollen taproot reaches maturity.[22][23] In its biennial life cycle, the first year is dedicated to vegetative growth and storage root formation, followed by bolting and seed production in the second year after vernalization.[17][20]Varieties and Cultivars
Turnip varieties are broadly categorized into root-focused and leaf-focused types, with selections emphasizing tenderness, size, and storage quality for culinary or forage use. Root-focused cultivars, such as the white-fleshed 'Purple Top White Globe', produce small, globe-shaped roots measuring 2 to 3 inches in diameter with purple shoulders and white flesh, ideal for fresh human consumption due to their mild flavor and tender texture.[1] Larger varieties like the yellow-fleshed 'Golden Ball' or 'Yellow Globe' develop 3- to 4-inch amber roots suitable for long-term storage, offering a sweet, non-woody interior that resists pithiness even at maturity.[24] These white- and yellow-fleshed groups represent primary divisions in turnip root cultivars, with white types dominating European selections and yellow ones valued for their color and flavor retention.[25] Leaf-focused varieties prioritize abundant, mild greens over root development, often yielding harvests in 30 to 40 days. Cultivars like 'Seven Top' and 'Shogoin' produce tall plants with broad, tender leaves high in vitamins, commonly grown for greens in both home and commercial settings, though their roots remain small and secondary.[19] 'Shogoin', a traditional Japanese type, features fine-grained white roots alongside its foliage, making it versatile for dual harvest, while 'Alltop' focuses almost exclusively on tops with minimal root formation.[26] Asian selections such as 'Hakurei' emphasize salad-quality roots that are crisp and buttery, with flat to round shapes adapted for quick cooking or raw use.[19] Turnips exhibit regional adaptations, with European varieties typically featuring white-fleshed, globe-shaped roots suited to cooler climates, contrasting Asian types like 'Shogoin' that form larger, flatter roots resilient in warmer conditions.[25] This distinction often leads to confusion with rutabaga (Brassica napus), a related but distinct species with larger, yellow-fleshed roots and a cross between turnip and cabbage.[19] Breeding efforts for turnips have emphasized hybrid vigor and disease resistance since the early 20th century, transitioning from heirloom open-pollinated types like 'Purple Top White Globe' to modern F1 hybrids developed by private seed companies.[25] Japanese breeders have pioneered F1 hybrid white turnips with improved uniformity and yield, while global programs select for resistance to clubroot (Plasmodiophora brassicae), incorporating dominant genes from resistant landraces into elite lines for sustainable cultivation.[27] For instance, European fodder turnips like ECD04 have been bred for multiple clubroot pathotypes through marker-assisted selection, enhancing field performance without yield penalties.[28]Nutritional Profile
Composition
Turnip roots and greens are low-calorie vegetables with high water content and a composition dominated by carbohydrates and fiber, alongside notable micronutrients and bioactive compounds. The roots consist primarily of water, approximately 92% by weight, which contributes to their crisp texture and low energy density.[29] Turnip greens, similarly, are about 90% water, supporting their role as a hydrating leafy green. Both parts contain negligible amounts of fat (0.1 g per 100 g) and no cholesterol, making them suitable for low-fat diets.[30] The macronutrient profile of boiled turnip roots provides 22 kcal per 100 g, with 5.1 g of carbohydrates (including 1.8 g of dietary fiber), 0.7 g of protein, and minimal fat.[31] Raw turnip greens offer 32 kcal per 100 g, comprising 7.13 g of carbohydrates (with 3.2 g of fiber), 1.5 g of protein, and 0.3 g of fat.[30] These values reflect the vegetables' status as nutrient-dense yet energy-light foods, with fiber aiding digestive health. Nutritional data per USDA FoodData Central (accessed 2025).| Nutrient (per 100 g) | Boiled Turnip Roots | Raw Turnip Greens |
|---|---|---|
| Energy | 22 kcal | 32 kcal |
| Carbohydrates | 5.1 g | 7.13 g |
| Dietary Fiber | 1.8 g | 3.2 g |
| Protein | 0.7 g | 1.5 g |
| Total Fat | 0.1 g | 0.3 g |