Brassica is a genus of roughly 40 to 45 accepted species of flowering plants in the mustard family, Brassicaceae (order Brassicales). The name was used by Pliny the Elder for several cabbage-like plants, and Linnaeus formally circumscribed the genus, which today carries the authority "Brassica L." in standard checklists. Members are mostly annual or biennial herbs — some growing as small shrubs — with simple or branched stems that are often glaucous (covered in a waxy bloom), lyrate-pinnatifid lower leaves, and entire upper leaves that frequently clasp the stem. The flowers are unmistakably cruciferous: four petals, typically bright yellow, arranged in a cross, with six stamens in the characteristic Brassicaceae pattern of four long and two short.
The genus is native to Western Europe, the Mediterranean basin, and temperate Asia, with the Mediterranean region forming its evolutionary center of diversity. From that homeland the most useful species have travelled with agriculture for millennia, and many have escaped cultivation to become widely naturalized — and frequently weedy — in North America, South America, southern Africa, and Australia. In the United States Southwest, regional checklists describe Brassica as "coarse, weedy annuals and biennials" of Old World origin, and floras such as PlantZAfrica note that the three species naturalized in South Africa are not indigenous and have not been evaluated under that country's Red List.
Few plant genera have shaped human diets so thoroughly. Six species supply the bulk of the world's "cole crops" and oilseeds: Brassica oleracea (cabbage, broccoli, cauliflower, kale, Brussels sprouts, kohlrabi), Brassica rapa (turnips, Chinese cabbage, pak choi, mizuna, and field mustard), Brassica napus (rapeseed/canola and swede), Brassica juncea (Indian or brown mustard), Brassica nigra (black mustard), and Brassica carinata (Ethiopian mustard). Rapeseed oil is the world's third-largest source of vegetable oil. More than thirty wild species and hybrids are also in cultivation, alongside an enormous body of cultivars and farmer-selected hybrids, making Brassica one of the most agriculturally productive — and historically important — genera in the temperate world.
Etymology
The genus name Brassica was used by Pliny the Elder in classical Roman times to refer to several cabbage-like plants. Linnaeus retained the name when formally establishing the genus in the eighteenth century, and the standard taxonomic authority cited in modern checklists is "Brassica L."
Distribution
Brassica is native to Western Europe, the Mediterranean basin, and temperate regions of Asia, with the Mediterranean acting as its center of diversity. Regional floras document its long history of cultivation and escape: in Switzerland the national flora records at least seven species (B. fruticulosa, B. juncea, B. napus, B. nigra, B. oleracea, B. rapa, and B. repanda), and in the US Southwest the SEINet checklist enumerates roughly 49 taxa, all treated as Old World in origin. Many wild Brassica species are now widely naturalized as weeds in North America, South America, southern Africa, and Australia. In South Africa, three species have naturalized but none are indigenous.
Ecology
Most Brassica species are seasonal — annuals or biennials — with a few woody, small-shrub members. Floral architecture is the family's classic cruciform: four petals (usually yellow), six stamens in the characteristic 4-long-and-2-short tetradynamous arrangement, and erect or spreading sepals. The plants are typically glabrous or carry simple hairs, and many are glaucous; lower leaves are lyrate-pinnatifid, and the upper leaves are mostly entire and sessile. In disturbed or marginal habitats, wild species behave as "coarse, weedy annuals and biennials," with dwarf, stunted morphs appearing under unfavorable conditions.
Cultivation
Brassica is one of the most heavily cultivated plant genera in temperate agriculture. Over thirty wild species and hybrids are grown deliberately, alongside an extensive catalogue of cultivars and crosses developed for vegetable, oilseed, condiment, and forage use. Six species do most of the work: B. oleracea, B. rapa, B. napus, B. juncea, B. nigra, and B. carinata together account for cabbage, broccoli, cauliflower, kale, Brussels sprouts, turnip, Chinese cabbage, rapeseed/canola, and the various mustards.
Cultural & economic uses
The genus is of immense global economic importance. Brassica species are consumed as leafy and head vegetables (cabbage, kale, broccoli, cauliflower), root vegetables (turnips, swedes), condiments (yellow and brown mustards from B. nigra and B. juncea), and oilseeds (rapeseed/canola from B. napus, which is the world's third-largest source of vegetable oil). Several species also serve as animal forage and cover crops.
Conservation
Brassica is not generally a genus of conservation concern: it includes some of the world's most widely cultivated crops and many widespread weedy species. Where Brassicas occur outside their native range — for example in South Africa, where three species are naturalized — local Red Lists do not evaluate them because they are not indigenous. None of South Africa's naturalized Brassica species are declared invasive there.
Taxonomy notes
Brassica L. is an accepted genus of family Brassicaceae (order Brassicales). The GBIF backbone records 226 descendants under the genus (species plus infraspecific taxa). Counts of accepted species vary modestly between sources: Wikipedia gives approximately 45, SANBI PlantZAfrica gives approximately 40, and regional checklists like SEINet enumerate about 49 taxa for the US Southwest alone, reflecting cultivars, hybrids, and naturalized strays as well as accepted species.
