Physalis philadelphica.

The tomatillo is not at all what it seems. Despite its Spanish name tomatillo, "little tomato," it has no direct botanical link with the tomato: it's a species of the genus Physalis, a cousin of the ground cherry (which is smaller and sweeter, Physalis pruinosa), the South American cape gooseberry, and the famous ornamental Chinese lantern. More surprising still: the tomatillo historically precedes the tomato in Mexican cuisine. Domesticated by the Mesoamerican peoples of central Mexico probably 4,000 to 7,000 years ago, the tomatillo was the reference "tomato" of the Aztecs long before true Solanum lycopersicum arrived from the south of present-day Peru.

The Aztec word tomatl — from which the French tomate (and English tomato) comes — originally designated the tomatillo (miltomatl meaning specifically the tomatillo in the milpa, the Nahua kitchen garden). The meaning later shifted to the red fruit-tomato imported from the south. Today, the tomatillo remains the essential ingredient of salsa verde, chile verde, enchiladas suizas and pozole verde — all of Mexico's "green" cooking rests on it.

A spreading, branched plant 80 cm to 1 m tall, with light foliage and yellow flowers flecked with purple. Spectacular particularity: each fruit is wrapped in a thin papery green calyx that grows along with it, like a miniature Chinese lantern; the husk eventually splits or yellows when the fruit reaches full maturity, at which point it has grown from the size of a large table cherry to that of a small golf ball. The flesh is firm, juicy, pale green, with numerous small edible seeds. A unique flavour — tart, lemony, herbaceous, slightly resinous — completely different from the tomato's; a green freshness, almost apple-and-lemon, that structures the salsa verde sauces.

Uses are almost all Mexican: raw salsa verde (tomatillo, onion, garlic, serrano chili, cilantro, salt, briefly blended), cooked or roasted salsa verde (the same ingredients pan-fried or oven-roasted before blending, for a deeper, caramelized version), chile verde (a slow-simmered stew of pork and tomatillos that defines the great cooking of New Mexico), enchiladas suizas draped in salsa verde and gratinéed with cheese. Tomatillos are used green at full maturity (the great tradition), but can also be left on the plant until the husk turns fully yellow for a milder, fruitier flavour.

Grower's tip: A crucial thing to know before planting: the tomatillo is self-sterile (incompatible with its own pollen). You must therefore IMPERATIVELY plant at least two plants so they can pollinate each other. A single plant will flower abundantly but produce no fruit — one of the great classic garden disappointments for those who don't know. Start indoors 6-8 weeks before last frost, at 22-25 °C; cultivation similar to the tomato. Transplant once all frost risk has passed (late May to early June in Québec). Staking is very useful: the spreading plant tends to lie on the ground under the weight of the fruits, and fruits in contact with the soil rot or get eaten by slugs. Harvest when the husks begin to split or yellow, or when you feel the fruit fully fills the lantern. A generous variety — a single well-established plant can give 100 to 200 fruits in peak season. Excellent keeper in their husks in the fridge (2-3 weeks) or in the freezer (whole, without husk, for months for winter sauces).

• Open-pollinated. Annual. Self-sterile — requires at least two plants for cross-pollination. Insect-pollinated; crosses with other tomatillos (green, purple varieties) but NOT with tomatoes or ground cherries.
• Height: 80-100 cm, spreading habit.
• Maturity: 70-80 days after transplant.
• Exposure: full sun, warmth.
• Rich, well-drained, warm soil. Space plants 60 cm apart. Staking recommended.
• Start indoors 6-8 weeks before last frost. Transplant late May to early June in Québec once all frost risk has passed.