Cucumber

Cucumber (Cucumis sativus) is an annual trailing/climbing herb with stems 1–3 m long, angular and covered in stiff hairs, climbing by unbranched tendrils borne in the leaf axils. The leaves are alternate on long petioles, cordate to polygonal in outline, divided into 3–5 shallow lobes with finely toothed margins, and hairy on both surfaces. The flowers are unisexual on the same plant: male flowers are borne in clusters in the axils, female flowers are usually solitary with a swollen inferior ovary that already resembles a tiny fruit below the calyx; the petals are yellow and fused at the base. The fruit is a false berry (pepo), cylindrical, 5–30 cm long (some cultivars to 50 cm), with a green rind (sometimes white or yellow), smooth or bearing soft spines/tubercles; the flesh is pale green, crisp and juicy (about 95% water), and the centre holds many flat, cream-white seeds. The main cultivar groups are fresh-eating (slicing) cucumbers, small spiny pickling cucumbers, and seedless greenhouse types (parthenocarpic, female-flowering).

According to Kew POWO, Cucumis sativus is native from the Himalaya to China (Yunnan, Guizhou, Guangxi) and N. Thailand; the native countries include Assam, Bangladesh, China (South-Central and Southeast), East Himalaya, Myanmar, Nepal, Thailand and West Himalaya. The species was domesticated about 3,000 years ago in the Himalayan foothills from the wild C. sativus var. hardwickii; genetic evidence (Qi et al., Nature Genetics, 2013) supports a single domestication centre in India–Himalaya, from which the plant spread to China, the Mediterranean and Europe. Cucumbers were grown long ago by the Egyptians, Greeks and Romans; the Roman emperor Tiberius had them grown year-round in mobile glasshouses, and the Spanish brought the plant to the Americas in 1494. Today cucumber is grown worldwide; China produces more than three-quarters of the global crop, followed by Turkey, Russia, Iran, the USA and Mexico. In Vietnam cucumber is grown year-round in the Red River Delta, the Southeast, the Mekong Delta and Lam Dong (field and greenhouse crops).

Chemically, the cucumber fruit is about 95% water; its dry matter is mainly carbohydrate, fibre and a little protein, together with vitamin C, vitamin K, potassium, magnesium and some B vitamins. Its characteristic actives are the cucurbitacins — triterpenes responsible for bitterness; in cucumber the main bitter compound is cucurbitacin C, controlled by the Bl and Bt genes in the cucurbitacin biosynthetic pathway (Shang et al., Science, 2014). The fresh aroma comes mainly from (E,Z)-2,6-nonadienal (the 'cucumber aldehyde'), together with (E)-2-nonenal and other C9 compounds. The fruit also contains cucurbitacin B, cucurbitacin C glucoside, flavonoids (quercetin, apigenin, luteolin), phenolic acids (caffeic and chlorogenic acid), saponins, tannins and an antioxidant protein. The cucumber genome was first sequenced in 2009 (Huang et al., Nature Genetics 41:1275–1281), and a large genome variation map was published in 2013 (Nature Genetics 45:1510–1515), clarifying the molecular basis of bitterness and fruit traits.

Cucumber is a major fruit vegetable: the young fruit is eaten raw with salt or fish sauce, in salads and pickles (dưa góp, sweet-and-sour pickle), stir-fried and in soups; it is juiced as a cooling drink and for smoothies; it is also used in face masks, and the pickle industry processes large volumes for export. In research, the cucumber genome (Huang et al., Nature Genetics, 2009) was among the first plant genomes sequenced and helped identify fruit-trait genes; in 2013 a genome variation map of many accessions (Nature Genetics) clarified domestication and diversity; and in 2014 the cucurbitacin C biosynthetic pathway and its regulation by the Bl/Bt genes were published in Science. A 2024 study quantified cucurbitacin C in fruit and showed that fermentation (pickling) markedly lowers its level, helping reduce bitterness. Cucumber extracts and cucurbitacins show antioxidant, anti-inflammatory and anticancer activity in vitro; a 2025 review of the genus Cucumis summarises these pharmacological studies. Cucurbitacin C levels rise when the plant is chilled (below about 12 °C) or given heavy nitrogen (Kano & Goto, 2003).

As food, fresh cucumber is wholesome and low in calories and, being water-rich, helps with hydration. However, like other cucurbits it can accumulate cucurbitacin C and become unusually bitter — especially when the plant is chilled, over-fertilised with nitrogen or genetically predisposed — and eating strongly bitter fruit can cause cucurbitacin poisoning with gastrointestinal symptoms such as nausea, vomiting, diarrhoea and abdominal pain; therefore never eat a fruit with a strong bitter taste. Pickled cucumber is high in sodium, so people with hypertension should mind their intake; people allergic to pollen or latex may experience oral allergy syndrome (OAS) when eating raw cucumber. On conservation, according to Kew POWO, Cucumis sativus is regarded as Least Concern and is not listed in the CITES appendices; it is a global crop and so not threatened. The main risk is erosion of the genetic resources of the wild C. sativus var. hardwickii and the wild relatives in the genus Cucumis — valuable gene sources for disease resistance, cold tolerance and fruit quality — so conserving landraces and wild relatives in genebanks is a priority.