Plant 274

Capsicum species (Solanaceae)

Chilli peppers

The pungency of chillies is due to a specialized metabolite, capsaicin, concentrated in tissues that surround the seeds inside the fruits. Capsaicin content is subjectively measured using Scoville heat units (SHU), i.e., how much a chilli extract must be diluted before its 'heat' is undetectable. Capsaicin contents vary from absent in bell peppers through jalapeño (2,500-5,000 SHU) and habanero (100,000-350,000 SHU) to extremes such as the 'Trinidad Moruga Scorpion' (2,000,000 SHU). Synthetic capsaicin is used in pepper sprays.

Capsicum is a small genus of approximately 25 species that, in pre-Columbian times, was restricted to the Americas. Five Capsicum species were domesticated in the Americas, although the regions of their domestication remain informed speculation: Capsicum annuum (bell pepper and jalapeño) in Mexico or northern South America; Capsicum frutescens (tabasco) in the Caribbean; Capsicum chinense (habanero and Scotch bonnet) in Amazonia; Capsicum baccatum (aji) in Bolivia; and Capsicum pubescens (rocoto) in the southern Andes. Domestication focused on the fruits; small, erect, deciduous red fruits of the wild forms were unconsciously selected to produce large, hanging, persistent, multi-coloured fruits. Along with these features came changes in capsaicin content and other compounds that give chillies their characteristic flavours. Although all five species contribute to the global spice trade, Capsicum annuum is the most important.

Chillies were cultivated and used in complex food cultures across the Americas from the Caribbean to the Andes six millennia ago, although they were probably harvested from the wild at least one millennium before this.

The first mention of chillies in western literature was by Diego Álvarez Chanca, physician on Columbus's second voyage in 1493, under the Taino name agi. The name chilli derives from the mainland Nahuatl name that the Spanish later encountered in Mexico in the 1520s. Interest in this new spice established itself rapidly across Europe. The first printed illustrations of chillies were published in the German botanist Leonard Fuchs' De Historia Stirpium (1543). By 1597, the English herbalist John Gerard reported that chillies were 'very well knowne in the shoppes at Billingsgate by the name of Ginnie pepper, where it is usually to be bought', although he had little success cultivating them.

Chillies spread rapidly to the Asian possessions of the Spanish and Portuguese Empires so that by the end of the sixteenth century it was established in China, India, Indonesia and Japan, whence it started to follow the trade routes from Asia back into Europe.

Kim S et al. 2014. Genome sequence of the hot pepper provides insights into the evolution of pungency in Capsicum species. Nature Genetics 46: 270-278.

Knapp S 2007. Some like it hot. Science 315: 946-947.

van Zonneveld M et al. 2015. Screening genetic resources of Capsicum peppers in their primary center of diversity in Bolivia and Peru. PLoS ONE 10: e0134663.

Stephen Harris

The 25th July 2021 marks 400 years of botanical research and teaching by the University of Oxford.

As a celebration and count-down to this anniversary, the University of Oxford Botanic Garden and Arboretum, together with the Oxford University Herbaria and the Department of Plant Sciences, will highlight 400 plants of scientific and cultural significance. One plant will be profiled weekly, and illustrated with images from Oxford University's living and preserved collections.

Follow us on Twitter @Plants400

The data and images available on this site may only be used for scientific purposes. They may not be sold or used for commercial purposes. All images are copyright of the University of Oxford, unless otherwise indicated.

The specimens at the Oxford herbaria and the living collections of the Oxford Botanic Garden and Oxford University Herbaria are being digitized using BRAHMS.


Dr Stephen Harris (