Tropaeolum — the nasturtiums: a genus of ornamental and edible flowering plants

Distinctive features

Tropaeolum species share several recognizable traits: round, often peltate leaves attached at the center of the blade; brightly colored, zygomorphic flowers with a prominent nectar spur formed by one sepal; and stamens that are positioned to favor visits by particular pollinators. Many species climb or scramble by means of leaf petiole tendrils. The flowers occur in warm shades of yellow, orange, red and sometimes bi- or multicolored patterns, attracting insects and hummingbirds.

History and distribution

These plants evolved in the Americas and were brought into cultivation in Europe and elsewhere from the 16th century onward. The familiar garden form, Tropaeolum majus, has been widely selected for larger flowers and rounded, trailing habits. Some wild species are adapted to cooler Andean climates; for example, the tuberous Tropaeolum polyphyllum from parts of Chile can survive underground when air temperatures fall well below freezing.

Uses and cultivation

Gardeners prize nasturtiums for their long flowering season and simple cultural needs: they flourish in moderately poor, well-drained soils and in full sun, and they tolerate drought better than heavy feeding. Leaves and flowers are edible, with a peppery flavor used fresh in salads, as garnishes, or preserved; seeds of some varieties are pickled as a caper substitute. Cultivation notes often recommend sowing seeds in spring, providing support for climbing forms, and avoiding excessive fertilization which can reduce flowering.

Ecology and pollination

• Flowers provide nectar and pollen that attract a variety of pollinators, notably bees and hummingbirds in the Americas.
• Flower shape and spur length are matched to pollinator feeding behavior, an example of ecological specialization.
• Several species are used in companion planting because they can deter certain pests or attract beneficial insects.

Notable distinctions and facts

Although commonly called nasturtiums, Tropaeolum plants are not closely related to true watercresses (genus Nasturtium in the Brassicaceae). The genus name is Latin-derived and alludes to the shield-like (peltate) leaves. While most garden nasturtiums are frost-tender, a few species are hardy in cooler climates due to subterranean tubers or other overwintering structures.

For further classification details and species lists see resources on the genus and family: genus overview, cultivation guides for annual types and perennial forms, botanical descriptions of flowering plants, and regional floras for Central America, South America and specific notes from Chile.