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 in his book Species Plantarum and is the only genus in the family Tropaeolaceae. The nasturtiums received their common name because they produce an oil similar to that of watercress (Nasturtium officinale). The genus Tropaeolum, native to South and Central America, includes several very popular garden plants, the most common being T. majus, T. peregrinum and T. speciosum. One of the hardiest species is T. polyphyllum from Chile, the perennial roots of which can survive the winter underground at elevations of 3,300 metres (11,000 ft). Plants in this genus have showy, often intensely bright flowers and rounded, peltate (shield-shaped) leaves with the petiole in the centre. The flowers are bisexual and zygomorphic, with five petals, a superior three-carpelled ovary, and a funnel-shaped nectar spur at the back, formed by modification of one of the five sepals.
Description 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 entirely or palmately lobed. The petioles or leaf stalks are long and, in many species, can twine around 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.
Taxonomy Tropaeolum was named by Carl Linnaeus in his book Species Plantarum. He chose the genus name because T. majus reminded him of an ancient custom: After victory in battle, the Romans erected a trophy pole (or tropaeum, from the Greek tropaion, source of English "trophy") on which the vanquished foe's armour and weapons were hung. The plant's round leaves reminded Linnaeus of shields and its flowers of blood-stained helmets. Tropaeolum was previously placed in the family Tropaeolaceae along with two other genera, Magallana Cav. and Trophaeastrum. The monotypic genus Magallana was characterised by having winged fruit, and the two species of Trophaeastrum lacked spurs. The genus Tropaeolum 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 Magallana and Trophaeastrum were reduced to synonyms of Tropaeolum. Tropaeolaceae was thus rendered monogeneric, a family of only one genus. The nasturtiums received their common name because they produce an oil similar to that of watercress (Nasturtium officinale).
Species "The Plant List", a collaboration between the Missouri Botanical Garden and the Royal Botanic Gardens, Kew, includes the following accepted names of Tropaeolum species names. Some that are under review are here marked "U".
Cultivation
The most common flower in cultivation is a hybrid of T. majus, T. minus, and T. peltophorum. It is commonly known as the nasturtium (and occasionally anglicized as nasturtian). It is mostly grown from seed as a half-hardy annual, and both single and double varieties are available. It comes in various forms and colours, including cream, yellow, orange and red, solid in colour or striped and often with a dark blotch at the base of the petals. It is vigorous and easily grown and does well in sun. It thrives in poor soil and dry conditions, whereas rich soil produces 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 following cultivars have gained the Royal Horticultural Society's Award of Garden Merit:
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