Aji is a word, not a taxon. It came into Spanish from Taino, it means chili pepper across Spanish-speaking South America, and it attaches to plants in at least four Capsicum species. This page covers where those plants came from and how botanists sort them. For the full roster, our companion article on aji peppers by species lists all 183 aji records in the database with their species and heat ranges.

Where did aji peppers come from?

The Andes. Barboza and colleagues, in the 2022 monograph that remains the standard treatment of the genus, place the primary center of Capsicum diversity there and date human use of chilies to 6000 to 6500 BCE. Linda Perry's team reached the same era from a different direction in 2007. They recovered chili starch microfossils at seven archaeological sites from the Bahamas to southwestern Ecuador and Peru, often in the same deposits as maize.

The species domesticated in different places. Kraft and colleagues combined species distribution modeling, paleobiolinguistics, microsatellite data and archaeobotany in 2014 and landed on central-east Mexico for C. annuum, more than 6,500 years ago. C. baccatum, the species behind most ajis, came out of Bolivia, and the Peruvian coastal sites at Huaca Prieta and Punta Grande carry the earliest cultivated material. Peru holds more Capsicum diversity than any other country, and its national germplasm bank at INIA keeps hundreds of aji accessions across several species.

That separate history explains the confusion in the name. Andean growers were selecting baccatum in isolated valleys for thousands of years before anyone drew a species boundary, and the word aji arrived later, from the Caribbean, applied to whatever grew locally.

How the five domesticated species got their names

Linnaeus cut the genus down to two species in 1753: C. annuum for the herbaceous annual and C. frutescens for the shrubby perennial. The rest followed quickly. Linnaeus added C. baccatum in 1767, Jacquin described C. chinense in 1776 on a plant that never grew in China, and Ruiz and Pavon named C. pubescens in 1799 from Peruvian material. All five domesticates carried names by the early nineteenth century, and the arguments since have been about where the lines fall, not about which species exist.

How can I tell which species an aji is?

Look at the flower and the seed, not the pod. Pod shape in domesticated peppers varies so wildly that it identifies nothing. The characters below come from the Barboza monograph's identification key, and they hold up in a garden with no equipment beyond a hand lens.

Species.Flowers per node.Corolla.Fruiting calyx.Seeds.
C. annuum var. annuum.Solitary, rarely paired.8 to 15 mm, entirely white; petioles up to 10 cm.No prominent annular constriction at the pedicel junction.Pale yellow.
C. baccatum var. pendulum.Usually solitary.White with large greenish-yellow spots and a white center.No annular constriction; teeth conspicuous.Pale yellow.
C. chinense.2 to 4, sometimes 5.6.5 to 8 mm, dull white or greenish-white; petioles to 3.5 cm.Prominent annular constriction at the pedicel junction. The key character.Pale yellow.
C. frutescens.Often 2 or more.Greenish-white, glandular trichomes on the inner face.Deeply cup-shaped, no annular constriction; fruits erect and narrowly triangular.Pale yellow.
C. pubescens.Usually solitary.Purple.No annular constriction.Black to brownish-black. Unmistakable.

The annular constriction is the one worth learning. Turn a ripening pod over and look at the ring where the calyx meets the stem: a distinct pinched collar means C. chinense. Black seeds and purple flowers mean pubescens and nothing else. Spotted petals with a clean white center mean baccatum.

Every aji named on the old version of this page

The species column reports what the WikiPepper database holds. Two of these names have no record of their own, which is itself useful information when a seed listing quotes them.

Name.Species in the database.Note.
Aji Amarillo.C. baccatum.30,000 to 50,000 SHU. The Peruvian kitchen staple.
Aji Cristal.C. baccatum.10,000 to 50,000 SHU. Chilean, harvested green.
Aji Lemon Drop.C. baccatum.10,000 to 50,000 SHU. Also sold as Kellu Uchu.
Aji Fantasy.C. baccatum.5,000 to 15,000 SHU. Six color variants carry records of their own.
Aji Oro.No record.Circulates as a trade name; the database holds no separate entry.
Aji Charapita.C. chinense.30,000 to 50,000 SHU. Amazonian, pea-sized, expensive.
Aji Panca.C. baccatum.1,000 to 1,500 SHU. Species disputed; see below.
Aji Dulce.C. chinense.0 to 1,000 SHU. Aromatic and essentially sweet; six named variants.
Aji Guaguao.C. frutescens.30,000 to 50,000 SHU. Cuban, the one clear frutescens aji.
Aji Rojo.C. baccatum.10,000 to 50,000 SHU, not annuum as the old page claimed.
Aji Caribe.No record under that name.The database holds Caribe, an annuum at 5,000 to 30,000 SHU.
Aji Rocoto.C. pubescens, as Rocoto.Colloquial only. Rocoto is the standard name; 30,000 to 100,000 SHU.

Where the classification is genuinely contested

Aji Panca is the live argument. Peruvian sources and The Chile Pepper Almanac both call it C. chinense, citing multiple flowers per node and the calyx constriction. Other references and the current WikiPepper record call it C. baccatum. Nobody has published a side-by-side morphological study, so treat the species line on a Panca packet as unverified.

Aji Dulce catches people a different way. It is chinense, so it germinates slowly and wants a long warm season, yet it carries almost no heat. Growers who buy it expecting a sweet annuum get an eleven-week head start problem. Aji Charapita and Aji Limo are chinense too, and the old claim that chinense ajis are rare in South American cooking does not survive a trip to a Lima market.

What to do with this

Treat the word aji as a regional label and go to the species for anything that matters: start date, season length, spacing and support. Record the accession number when a packet carries one, because the number identifies the plant and the name does not. Every record on this site also carries a Universal Pepper Number encoding species, color, pattern, form and heat in one string. When two sellers disagree about what an aji is, compare the codes rather than the descriptions.

Sources & Further Reading