Cosmos caudatus is the scientific name for what Malaysians call “Ulam raja” (literally translated as Salad King), a plant belonging to the Asteraceae family. Cosmos is a Greek word for order or ornament, while caudatus comes from the Latin word which means tailed (Gledhill, 2002; Moshawih et al., 2017). It is often regarded as the "king of ulam" because it is highly nutritious and has numerous health benefits and medicinal properties (Shui et al., 2005). It is also believed that it was once served to Malay royalty, which is how it earned its name.
This species is native to North America and has since spread worldwide, including to subtropical and tropical countries (Bunawan et al., 2014). This plant is cultivated in Myanmar, the Philippines, Indonesia and Malaysia. Classified as an annual to short-lived perennial aromatic herb, it can grow up to 250 cm tall. It grows naturally in monsoonal deciduous forests, as well as on grassy banks and slopes (Datiles, 2022). Normally, it grows well in irrigated soil with moisture and full sunlight but grows larger when fertilised. The flowers, however, will be smaller (Moshawih et al., 2017).
The plant has more branches in the upper part. The stem is green or partially purple, and the leaves are easily distinguished by their triangular to deltate shape (Bunawan et al., 2014; Datiles, 2022). The flowers are usually violet or reddish and sometimes white or yellowish. The fruits are single-seeded and turn blackish when ripe. They are wind-dispersed due to their lightweight. Additionally, the fruits have hooks that allow them to attach to animals and humans, aiding in their dispersal.
Cosmos caudatus is a popular medicinal and culinary herb, primarily consumed as ulam by the Malay and Javanese communities, who eat its raw stems and leaves. Due to its antimicrobial properties, people have traditionally used this plant to treat burns and to relieve muscle strains and cramps (Moshawih et al., 2017). It is also believed to have anti-ageing properties, with its extracts traditionally used to prevent skin ageing (Loo et al., 2024). Additionally, the essential oil extracted from the plant has been used to eliminate bad breath (Moshawih et al., 2017). Cosmos caudatus is also thought to cure infectious diseases in the elderly, improve blood circulation and strengthen bones (Cheng, 2017).
Scientific research has supported many of its traditional uses, revealing antifungal, antibacterial, antioxidant, anti-osteoporosis and antidiabetic properties. Extracts from this species are rich in glycosides, which help prevent skin ageing (Loo et al., 2024). More research is needed, particularly on its anti-leishmanial and anti-thrombolytic properties (Ahda et al., 2023). While its medicinal potential has been explored, only one human clinical trial has confirmed its effectiveness in treating diabetes (Ahda et al., 2023). However, excessive consumption may lead to hepatotoxicity, making lower doses advisable (Bunawan et al., 2014). Current studies mainly focus on fresh leaves and crude extracts, so further clinical trials are necessary to verify their safety, effectiveness and specific active compounds. In agriculture, it is an effective pesticide, targeting caterpillars, aphids, diamondback moths and Dysdercus sp. (Murugesu et al., 2020).
