About 80 species, see text.
Tropaeolum //, commonly known as Nasturtium (//; literally "nose-twister" or "nose-tweaker"), is a genus of roughly 80 species of annual and perennial herbaceous flowering plants. It was named by Carl Linnaeus and is the only genus in the family Tropaeolaceae. The nasturtiums received their common name because they produce an oil that is similar to that produced by watercress (Nasturtium officinale).
The genus Tropaeolum, native to South and Central America, includes several very popular garden plants, the most commonly grown being T. majus, T. peregrinum and T. speciosum. The hardiest species is T. polyphyllum from Chile, the perennial roots of which can survive underground when air temperatures drop as low as −15 °C (5 °F).
Plants in this genus have showy, often intensely bright flowers, and rounded, peltate (shield-shaped) leaves with the petiole in the centre. The flowers have five petals (sometimes more), a three-carpelled ovary, and a funnel-shaped nectar tube at the back.
The first nasturtium species was introduced into Europe in the 18th century and was named Tropaeolum minus by the Swedish botanist Carl Linnaeus. He chose the genus name because the plant reminded him of an ancient custom. After victory in battle, the Romans used to set up a trophy pole called a tropaeum (from the Greek tropaion, source of English "trophy"). On this the armour and weapons of the vanquished foe were hung. Linnaeus was reminded of this by the plant as the round leaves resembled shields and the flowers, blood-stained helmets.
Nasturtiums were also known as "Indian cress". This was because, when they were introduced they were used as a salad ingredient and they originated from South America which at that time was known as the Indies. The 16th-century herbalist John Gerard, in his book "Of the Historie of Plants", called the plant "lark's heel". He wrote: "unto the backe part(of the flower) doth hange a taile or spurre, such as hath the larkes heele, called in Latine Consolida regalis." (He was referring to the forking larkspur (Consolida regalis).
Tropaeolum is a genus of dicotyledonous annual or perennial plants, often with somewhat succulent stems and sometimes tuberous roots. The alternate leaves are hairless, peltate and entire or palmately lobed. The petioles or leaf stalks are long and in many species are able to twine round other stems to provide support. The flowers are bisexual and showy, set singly on long stalks in the axils of the leaves. They have five sepals, the uppermost of which is elongated into a nectar spur. The five petals are clawed, with the lower three unlike the upper two. The eight stamens are in two whorls of unequal length and the superior ovary has three segments and three stigmas on a single style. The fruit is naked and nut-like, with three single seed segments.
Species in cultivation
The most common species in cultivation is a hybrid of T. majus, T. minus and T. peltophorum and is commonly just known as a nasturtium. It is mostly grown from seed as a half-hardy annual and both single and double varieties are available (doubles are mostly sterile and need to be propagated from cuttings). It comes in a range of habits and colours including cream, yellow, orange and red, either solid colour or striped and often with a dark blotch at the base of the petals. It is vigorous and easily grown and prefers a sunny spot. It thrives in poor soil and dry conditions whereas in rich soil it tends to produce much leafy growth and few flowers. Some varieties adopt a bush form while others scramble over and through other plants and are useful for planting in awkward spots or for covering fences and trellises.
The Canary creeper (Tropaeolum peregrinum) is a trailing and climbing species with wiry stalks and palmately lobed leaves. The pale yellow, fringed flowers are borne on long stalks. It originated from Peru but may first have been cultivated in the Canary Islands before being introduced into Western Europe.
Tropaeolum polyphyllum is a prostrate plant originating from Argentina and Chile. It has silvery, deeply lobed leaves and a profusion of small, bright yellow flowers on long trailing stalks. After flowering, the plant dies back. It is a perennial with underground rhizomes which send up new shoots at intervals. In a suitable sunny location with well drained soil, it will survive for several years.
The flame flower (Tropaeolum speciosum) is well adapted to cool, moist climates and does well in Scotland. It sends up shoots which thread their way through hedges and shrubs and which, when they emerge into the light, bear brilliant red flowers among small, five or six-lobed leaves. It needs a cool location for its roots and is difficult to establish, but when it thrives, it is a glorious sight. This plant has gained the Royal Horticultural Society's Award of Garden Merit.
Three-coloured Indian cress (Tropaeolum tricolor) is another tuberous, climbing species grown for its attractive red, purple and yellow tubular flowers. It comes from Chile and Bolivia and is a reliable winter-growing species. 
Mashua (Tropaeolum tuberosum) is a perennial climbing plant from the Andes, grown for its tuberous roots. It has been cultivated since ancient times and depictions of it are found at archaeological sites pre-dating the Incas. It has leaves with five to seven lobes and small, red and yellow, long-spurred flowers. The tubers have an unpleasant smell when raw which disappears on cooking. It is frost-hardy and produces crops of 30 tons per hectare at a height of 3,000 metres (9,800 ft) above sea level. The cultivar T. tuberosum lineamaculatum 'Ken Aslet' has gained the Royal Horticultural Society's Award of Garden Merit. 
Species that originated from the coastal areas and from the lower foothills make most of their growth in winter whereas the true alpine species are summer growers. Tuberous Tropaeolum species are well known for occasionally remaining dormant for one or more years. The species with underground rhizomes and tubers can be propagated from these while other species are best raised from seed. Fresh seed is favoured by many growers but dried seed is also often successful. Seed from the winter growing species should be sown in the autumn while the summer growing species are best sown in the spring in well-drained compost and covered with 1 to 2 cm (0.4 to 0.8 in) of grit or sand. The containers should be kept at below 4 °C (39 °F) until the seedlings appear in about a month, as too high a temperature inhibits germination.
All parts of T. majus are edible. The flower has most often been consumed, making for an especially ornamental salad ingredient; it has a slightly peppery taste reminiscent of watercress, and is also used in stir fry. The flowers contain about 130 milligrams (2.0 gr) vitamin C per 100 grams (3.5 oz), about the same amount as is contained in parsley. The unripe seed pods can be harvested and dropped into spiced vinegar to produce a condiment and garnish, sometimes used in place of capers.
Nasturtiums have been used in herbal medicine for their antiseptic and expectorant qualities. They are said to be good for a chest cold and to promote well being by the formation of new blood cells. Tropaeolum majus has been used in herbal medicine for respiratory and urinary tract infections.
Tropaeolum was previously placed in the family Tropaeolaceae along with two other genera, Magallan and Trophaeastrum. Magallan (1 species) was characterised by having winged fruit and Trophaeastrum (2 species) by having no spur while Tropaeolum (86 species) was diagnosed only by the absence of the characteristics of the other two genera. A molecular study undertaken in 2000 found Tropaeolum to be paraphyletic when the other two genera are segregated, so Magallan and Trophaeastrum were reduced to synonyms of Tropaeolum. Tropaeolaceae was thus rendered monogeneric.
"The Plant List" is a collaboration between the Missouri Botanical Garden and the Royal Botanic Gardens, Kew, England. It includes over a million species and for the genus Tropaeolum includes the following species. These are accepted names except for the ones marked "U", the validity of each of which is under review:
- Sunset Western Garden Book, 1995:606–607; "Tropaeolum". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005.
- "Nasturtium". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005.
- Perry, Frances (1972). Flowers of the World. The Hamlyn Publishing Group. pp. 298–300. ISBN 060001634x Check
- Allaby, Michael (ed.) (1992). The Concise Oxford Dictionary of Botany. Oxford: Oxford University Press. p. 418. ISBN 0198661630.
- McClintock, Elizabeth. "Tropaeolaceae: Nasturtium Family". Jepson Flora Project. Retrieved 2012-06-20.
- McFarlane, J. S. (2001-12-29). "The Genus Tropaeolum". Retrieved 2012-06-05.
- "Tropaeolum majus Alaska Series (v) AGM". Royal Horticultural Society. Retrieved 2012-09-08.
- "Tropaeolum majus 'Hermine Grashoff' (d) AGM". Royal Horticultural Society. Retrieved 2012-09-08.
- "Tropaeolum Whirlybird Series AGM". Royal Horticultural Society. Retrieved 2012-09-08.
- "Tropaeolum speciosum AGM". Royal Horticultural Society. Retrieved 2012-09-08.
- "Tropaeolum: Tropaeolum tricolor". Pacific Bulb Society. Retrieved 2012-06-23.
- "Mashua Ethnobotanical Leaflet". Southern Illinois University. Retrieved 2012-06-21.
- "Tropaeolum tuberosum var. lineamaculatum 'Ken Aslet' AGM". Royal Horticultural Society. Retrieved 2012-09-08.
- "Tropaeolum". Pacific Bulb Society. Retrieved 2012-06-23.
- "Tropaeolum minus". Plants For A Future. Retrieved 2012-06-05.
- United States Department of Agriculture Research Service (2010). USDA National Nutrient Database for Standard Reference, Release 23. Nutrient Data Laboratory. Retrieved 2011.
- Owen, Marion. "Poor Man's Capers: How to make gourmet capers from nasturtium seed pods". Retrieved 2012-06-24.
- Portrait of a Medicinal Plant (Original title: Portraet einer Heilpflanze. Tropaeolum majus L. - die Kapuzinerkresse. Merkurstab 1995; 48:357-62. English by A. R. Meuss, FIL, MTA.)
- Andersson, Lennart and Andersson, Stephan (2000). "A molecular phylogeny of Tropaeolaceae and its systematic implications". Taxon (Taxon, Vol. 49, No. 4) 49 (4): 721–736. doi:10.2307/1223973. JSTOR 1223973.
- "Trapaeolum". The Plant List. 2010. Retrieved 2012-06-23.
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