Tropaeolum, commonly known as nasturtiums, is a genus of roughly 80 species of annual and perennial herbaceous flowering plants, and the sole genus within the family Tropaeolaceae. Plants are native to South and Central America, with the greatest diversity concentrated in the Andes Mountains and Chile, where some species persist at elevations above 3,300 meters.
The genus is immediately recognizable by its two defining features: rounded, peltate (shield-shaped) leaves and brilliantly colored flowers. Flowers are composed of five petals in shades ranging from yellow through orange to deep red, with a distinctive funnel-shaped nectar spur formed from modified sepals. Many varieties are fragrant. Depending on the species, plants grow as compact mounds or as twining climbers reaching several meters, supporting themselves by wrapping their leaf stalks around neighboring vegetation.
Tropaeolum majus, the garden nasturtium, is by far the most widely cultivated member and serves as the familiar ornamental annual of temperate gardens worldwide. Other species — including the tuberous T. tuberosum (mashua), grown as a food crop in the Andes, and the Chilean species T. azureum with its rare blue flowers — reflect the genus's botanical diversity.
All parts of most Tropaeolum species carry a peppery, pungent flavor similar to watercress, and the genus has long been used in food and medicine across its native range and in Europe. The high vitamin C content of T. majus flowers and their use as a basis for the German herbal preparation Angocin Anti-Infekt N illustrate the genus's ongoing relevance beyond ornamental horticulture.
Etymology
The genus name Tropaeolum was coined by Carl Linnaeus and derives from the Latin tropaeum (Greek: tropaion), meaning a trophy or victory monument — the pole on which Roman soldiers hung the armor of defeated enemies. Linnaeus chose the name because the plant's rounded peltate leaves resembled shields, and its helmet-shaped flowers, stained in red and orange, resembled blood-stained helmets mounted on such a trophy. The common name "nasturtium" comes from Latin and literally means "nose-twister" or "nose-tweaker," a reference to the sharp, pungent oils of the plant that stimulate the nose much as watercress (Nasturtium officinale) does, though the two genera are botanically unrelated and belong to different families.
Distribution
Tropaeolum is native to the Americas, with its center of diversity in South America. The Andes mountain chain, running through Colombia, Ecuador, Peru, Bolivia, and Chile, supports the greatest species richness, and several species grow at elevations exceeding 3,300 meters. Chile is particularly notable for harboring species adapted to Mediterranean-type climates. The genus also extends northward into Central America and Mexico. Tropaeolum majus has been widely naturalized outside its native range as an ornamental escape, and is documented in the Swiss flora, though it carries no protection status there.
Taxonomy
Tropaeolum L. was formally described by Linnaeus in Species Plantarum 1: 345, published in 1753, and its taxonomic status is accepted without nomenclatural issues. The genus is the sole member of the family Tropaeolaceae, placed within the order Brassicales, which also includes the mustard family (Brassicaceae) and capers. GBIF records 181 descendant taxa (species and infraspecific ranks combined), while morphological treatments recognize approximately 80 accepted species.
Numerous earlier genus names have been reduced to synonymy under Tropaeolum, including Acriviola Mill., Anisocentra Turcz., Cardamindum Adans., Chymocarpus D.Don, Magallana Cav., Rixea C.Morren, Tropaeastrum D.J.Mabberley, Trophaeastrum Sparre, and Trophaeum L. ex Kuntze. These synonyms reflect a long history of independent description of subgroups within the genus before taxonomic consolidation.
Ecology
Tropaeolum species occupy a broad range of ecological niches, from sea-level coastal scrub to Andean montane habitats above 3,300 meters. Climbing and twining species support themselves on neighboring vegetation, using their peltate-petioled leaves as grasping organs. The nectar spurs of Tropaeolum flowers point to pollination by long-tongued insects and hummingbirds, the latter being primary pollinators across the genus's Andean range. In cultivation and in naturalized populations, Tropaeolum is attractive to butterflies and other pollinators, and plants are notably deer-resistant. Cabbage white butterfly caterpillars (Pieris spp.) are a significant herbivore, frequently attacking the foliage; the peppery glucosinolate compounds that deter vertebrate browsing do not deter these specialist Brassicales feeders.
Cultivation
Tropaeolum species, particularly T. majus, are among the easiest flowering annuals to grow. They thrive in full sun with some afternoon shade in hot climates, and perform best in poor, well-drained soils. Fertilization is counterproductive: excess nutrients shift energy toward foliage at the expense of flowers. Plants tolerate clay, loam, and light soils, and manage both dry and moderately moist conditions.
Cooler summer temperatures favor the best flowering, which is why nasturtiums often fade in midsummer heat and revive in autumn. Most cultivated forms are frost tender and rated for USDA zones 8-11 as perennials, though they are grown as cool-season annuals across virtually all zones. Some Andean species tolerate temperatures down to approximately -5 °C.
Propagation
The primary propagation method is seed, sown in spring. Because Tropaeolum seedlings have brittle roots and resent root disturbance, direct sowing in the final location is preferred outdoors; where indoor starting is used, biodegradable peat or paper pots minimize transplant shock. Seeds germinate readily without pre-treatment. Perennial tuberous species such as T. tuberosum can be propagated by tuber division in late summer, and basal stem cuttings taken in spring are viable for perennial species and named cultivars.
Uses
Tropaeolum has been cultivated for food, medicine, and ornament for centuries. All parts of T. majus are edible and carry a peppery, pungent flavor: flowers, leaves, seeds, and green seed pods are used fresh in salads, as garnishes, and pickled. The flowers are nutritionally notable, containing approximately 130 mg of vitamin C per 100 grams and exceptionally high levels of the carotenoid lutein.
Medicinally, the genus has been used in herbal traditions for respiratory and urinary tract infections, a use formalized in the German licensed herbal medicine Angocin Anti-Infekt N, which combines T. majus with horseradish root. The tuberous Andean species T. tuberosum (mashua) has been cultivated as a staple food crop in the high Andes for millennia.
