The Tomato Family Tree,
For People Who Grow Them

DNA settled a 250-year argument: tomatoes sit deep inside the genus Solanum, sister to the potatoes. Linnaeus named the tomato Solanum lycopersicum in 1753 and was right the first time. Its whole family lives in western South America — Andean slopes, coastal fog deserts, cloud forests, and the Galápagos — and by wild-tomato standards, everything about your garden plant is exotic: the red fruit, the self-pollinating flower, the annual lifestyle, even its existence outside South America.

Counts and claims: Peralta, Spooner & Knapp 2008 (abstract, introduction, and economic-value chapters).

Two outgroup sections — desert shrubs and cloud-forest lianas — then the 13 true tomatoes in four informal groups. Notice where color lives: only the youngest branch, the Lycopersicon group, makes red or orange fruit. Green, striped, and fuzzy is the family default. The crop and its lookalike, the currant tomato, are sister species at the very tip.

Click a group to isolate it. Hover any species for its story.

Every wild relative is packed into western South America and the Galápagos — most of them into Peru alone. The crop is the exception: it exists only in cultivation, and even the monograph's authors can't say whether people first domesticated it in Peru, in Mexico, or in both places independently. There are no archaeological tomato remains anywhere. For a crop this important, that's a remarkable hole in the record.

The tomato reached Europe as a suspected poison filed next to the mandrake, got named after a fruit Galen described that it could not possibly be, and spent 240 years in the wrong genus. It's been an eventful five centuries.

Of seventeen species, only these four ripen red, orange, or yellow — the crop, its free-crossing wild twin, and two island endemics Darwin collected. Everything else in the family ripens green.

Tomato flowers pay in pollen only — there's no nectar — and the pollen is locked inside a cone of fused anthers that has to be vibrated open. Bumblebees and other native bees do this expertly; honeybees physically can't. So when tomatoes reached a Europe with no buzz-pollinating bee service, only the flowers that could pollinate themselves set fruit — and generation by generation, growers unknowingly selected the stigma down inside the cone. The self-pollinating tomato flower is a domestication artifact, made by an absence of bees.

Diagram drawn from the monograph's flower descriptions and its account of Rick's (1995) stigma-position work. The same wild-to-selfing shift happens naturally at wild species' range edges — the crop just did it under human management.

Charles Rick spent decades answering exactly this, and the pattern he found still rules breeding: an Esculentum complex that crosses with the crop, and a Peruvianum complex that mostly refuses — the barrier isn't just the flower, it's the endosperm arithmetic (a 2:1 maternal-to-paternal balance the hybrid seed must satisfy). Plus one species that only donates pollen one way, and two that have never crossed with anything.

From the monograph's breeding-systems chapter, Rick's crossability complexes, and the EBN analysis it reviews (Ehlenfeldt & Hanneman 1992). "Lab help" = embryo rescue.

Here's the monograph's most useful myth-bust: the "wild cherry tomato" is not the wild ancestor. The plants long called "var. cerasiforme" are a scramble of feral crop escapes and crop-wild hybrids — which is why the monograph refuses to recognize the name. So what IS that vigorous little volunteer in your compost pile? The authors use a seven-point rule of thumb to separate true S. pimpinellifolium from escaped S. lycopersicum; a majority of marks carries the verdict. Try it on your plant.

Checklist translated from the identification rule in the monograph's S. pimpinellifolium treatment. Hybrids are common where the species meet — a mixed scorecard usually means exactly that.

Modern selfing bottlenecked the crop's genetics hard — and wild species have been paying the debt back for eighty years. If your seed packet mentions nematode, mildew, or virus resistance, a wild tomato from Peru is in the pedigree. The germplasm lives at UC Davis's Tomato Genetics Resource Center, founded by Rick from these very species.