Nasturtium

Botanical Profile

Note on species differentiation: Sweet orange (Citrus sinensis) and bitter orange (Citrus × aurantium) should be considered separately in botanical and phytochemical statements.

Nasturtium is Tropaeolum majus, an ornamental and useful plant of the Tropaeolaceae originally from South America. The herb is characterised by round peltate leaves, brightly coloured spurred flowers and a glucosinolate-like mustard-oil glycoside profile dominated by glucotropaeolin.

Tropaeolum majus L. belongs to the Tropaeolaceae. The species originates from South America, particularly the Andean regions and adjacent areas, and has been distributed in Europe since the early modern period as an ornamental, culinary and garden plant. Today it is cultivated in many temperate and subtropical regions and may occasionally naturalise in mild climates.

Botanically, it is an annual to short-lived perennial herbaceous, creeping or climbing plant. The leaves are round to shield-shaped and borne on long petioles that often attach near the centre of the leaf. This peltate leaf arrangement is conspicuous. The leaves have water-repellent surfaces from which droplets can roll off.

The flowers are large, brightly coloured and usually yellow, orange to red. A characteristic feature is the long nectar-containing spur. Flower shape and colour made nasturtium a popular garden plant. The fruits split into mericarps that can also have a pungent-aromatic taste.

In plant use, primarily the fresh or dried herb, leaves, flowers and sometimes fruits are used. The plant is edible and is used in salads, herb mixtures and decorative foods because of its pungent, cress-like flavour. Botanically, however, it is not closely related to watercress or garden cress. The sensory similarity results from mustard-oil chemistry, not close taxonomic relationship.

Phytochemistry

The phytochemistry of Tropaeolum majus is shaped particularly by glucosinolate or mustard-oil glycoside contexts. Glucotropaeolin, a benzyl glucosinolate, is regarded as a characteristic compound. Enzymatic cleavage, particularly through myrosinase activity, can produce benzyl isothiocyanate and related degradation products. This substance group explains the pungent, cress-like taste.

The mustard-oil chemistry of nasturtium is especially interesting because the plant does not belong to the Brassicaceae. Although glucosinolates are typical of crucifers, they also occur in some other plant families. Tropaeolaceae therefore provide an important comparative case for the evolution of glucosinolate-type metabolic pathways.

Besides glucotropaeolin, nasturtium contains flavonoids, carotenoids, anthocyanins in coloured flowers, phenolic acids, chlorophyll and other secondary plant metabolites. Flower colour is determined by different pigment groups; yellow, orange and red flowers differ in their pigment profiles. Leaves, flowers and fruits have different constituent distributions.

Enzymatic dynamics are important for quality. Cutting, drying, heating and extraction influence myrosinase activity and isothiocyanate formation. Fresh plant material can therefore have a different profile from dried or heated material. This processing sensitivity is typical of mustard-oil glycoside plants.

Modern analytics uses HPLC, LC-MS, GC-MS and enzymatic methods to investigate glucosinolates and isothiocyanates. Plant part, harvest time, drying and processing are decisive for raw-material quality. Nasturtium thus combines culinary herb, ornamental plant and chemically specialised mustard-oil plant.

Traditional Uses

Nasturtium reached Europe from South America after European expansion and was initially valued primarily as an ornamental plant. Its striking flowers, rapid growth and easy cultivation made it popular in cottage, monastery and ornamental gardens. The round leaves and bright flowers shaped its distinctive appearance.

Over time, culinary use also became more important. Leaves and flowers were used in salads and herbal dishes for their pungent, cress-like flavour. Unripe fruits were occasionally pickled in a manner similar to capers. This use illustrates how an introduced ornamental plant was integrated into European culinary practice.

The traditional European classification of nasturtium is younger than that of many native herbs. It does not belong to the basic medieval European flora but to the early-modern circulation of plants between South America and Europe. Its history combines horticulture, exoticism, ornamental value and edible flowers.

In South American contexts, the genus Tropaeolum is also diverse. Some related species were used as food plants, including tuber-forming Tropaeolum species. Tropaeolum majus itself became internationally known particularly through garden culture and later herbal use.

Current Research

Modern research on Tropaeolum majus focuses on glucotropaeolin, isothiocyanate formation, pigments, horticulture, raw-material processing and quality analytics. One focus is enzymatic cleavage of glucosinolates and how fresh, dried or heated material develops different profiles. Myrosinase activity and processing conditions are central.

Phytochemical work investigates flavonoids, carotenoids and anthocyanins in addition to glucotropaeolin. The flowers provide an interesting model for pigment research because different colour forms exist. Leaves and flowers may have clearly different analytical profiles.

Chemotaxonomically, Tropaeolum majus is particularly interesting because glucosinolates occur outside the Brassicaceae. Comparative research on Tropaeolaceae, Brassicaceae and related orders helps clarify evolutionary pathways of this substance group. Nasturtium is therefore also relevant to fundamental questions of plant chemistry.

Horticultural research addresses cultivars, flower colours, growth forms, cultivation and disease susceptibility. The plant is grown as an ornamental and useful plant and is also suitable for edible-flower concepts. From a raw-material perspective, freshness, drying and microbial quality are important.

Overall, nasturtium is a good example of a plant in which botany, garden culture, food use and specialised secondary-metabolite chemistry converge. For a WestExtract profile, clear differentiation from true cresses and Brassicaceae is important.

Sources

• Plants of the World Online. Kew Science. Royal Botanic Gardens, Kew.
• Hager's Encyclopedia of Drugs and Medicinal Substances.
• PubMed-indexed specialist literature on Tropaeolum majus, glucotropaeolin and isothiocyanates.
• Specialist literature on the chemotaxonomy of glucosinolate-containing plants.
• Horticultural specialist literature on Tropaeolum majus.
• Standard references on edible flowers and culinary herbs.