Crosne

Stachys affinis is native to the temperate regions of China and Japan.

• Cultivated in China for centuries, where it is known as "can shu" (silkworm plant) for its tuber shape
• Also grown in Japan, where it is called "chorogi"
• Introduced to France in 1882 by the French consul in Shanghai
• Quickly adopted by French chefs and named after the town of Crosne (Essonne)
• Became a fashionable vegetable in Belle Époque Paris
• Now grown commercially in France, Japan, and on a small scale in the United States
• First described by the German botanist Friedrich Gottlieb Bartling in 1848
• The genus Stachys contains approximately 300 to 450 species worldwide

A perennial herb growing 30 to 60 cm tall, spreading by underground stolons.

Stems:
• Erect, square (characteristic of Lamiaceae), green to purplish, hairy
• Branched from the base

Leaves:
• Ovate to cordate, 3 to 8 cm long and 2 to 5 cm wide
• Dark green, wrinkled (rugose), hairy on both surfaces
• Crenate to serrate margins
• Opposite arrangement (characteristic of mints)
• Short petioles

Flowers:
• Small, pink to purplish-pink, 1 to 1.5 cm long
• Born in whorled spikes in the upper leaf axils
• Two-lipped (bilabiate) corolla typical of Lamiaceae
• Blooms in late summer to autumn

Tubers:
• The edible portion — small, cylindrical, 3 to 8 cm long and 1 to 2 cm thick
• Segmented, with conspicuous constrictions giving a bead-like or caterpillar-like appearance
• Ivory white, thin-skinned
• Crisp, watery, sweet-nutty texture
• Form on slender stolons radiating from the base of the plant

Stachys affinis occupies an interesting ecological niche as a temperate, tuber-producing member of the mint family.

Habitat:
• Native to the temperate regions of China and Japan
• Found in moist, well-drained mountain soils along forest margins, stream banks, and in disturbed, fertile ground
• Grows at elevations of 100 to 2,000 meters in temperate East Asian climates
• Prefers cool, moist conditions with well-distributed rainfall and mild summers
• USDA zones 4–8 (very cold-hardy, requires winter chill for dormancy)

Growth Habit:
• Low-growing, spreading perennial herb, 30 to 60 cm tall, that dies back to the ground in winter
• Spreads aggressively by underground stolons that produce chains of small, bead-like tubers
• Prefers partial shade to full sun; tolerates a wide range of light conditions
• Cool-season grower — emerges in spring, grows through autumn, and is harvested after first frost

Pollination:
• Small, pink to purplish two-lipped flowers (typical of Lamiaceae) are primarily bee-pollinated
• Attracts long-tongued bees (Anthophora, Bombus) that access nectar from the deep corolla tube
• Flowers are produced in whorled spikes in summer but seed production is often sparse in cultivated forms
• Most reproduction and spread is vegetative via tubers rather than seed

Ecological Role:
• Dense foliage provides ground cover that suppresses weeds and reduces soil erosion
• Flowers are a valued nectar source for bees during the mid-summer nectar dearth period
• Tuber production improves soil structure — the stolons create channels that aerate the soil
• Can form dense colonies that exclude other herbaceous plants, acting as a living mulch
• Tubers are consumed by wild boar, rodents, and other fossorial mammals that dig them up

Invasive Status:
• Can spread persistently from unharvested tubers but is generally not considered invasive
• Tubers left in the ground will regrow reliably year after year
• Easily controlled by thorough harvesting of all tubers

Crosne tubers are a low-calorie vegetable with moderate nutrition.

• Per 100 g fresh tubers: approximately 35 to 45 kcal
• Contains approximately 8 to 10 g carbohydrates, primarily stachyose (a complex sugar)
• Low in protein (approximately 2 g per 100 g)
• Very low in fat
• Good source of dietary fiber
• Contains potassium, phosphorus, and iron
• Small amounts of vitamin C and B vitamins
• The carbohydrate stachyose is a prebiotic that feeds beneficial gut bacteria
• Very high water content (approximately 80%)

Propagated by planting small tubers.

• Plant tubers 5 to 8 cm deep in early spring, as soon as soil can be worked
• Space 20 to 30 cm apart in rows 40 to 60 cm apart
• Prefers loose, well-drained, fertile, sandy loam soils
• pH 6.0 to 7.0 is ideal
• Requires consistent moisture throughout the growing season
• Full sun to partial shade
• Tubers form in late summer to autumn
• Harvest after the foliage dies back in late autumn to early winter
• Harvest by carefully digging around the plant — tubers spread widely on stolons
• Some tubers inevitably remain in the ground and will resprout next spring
• Can be stored for several weeks in cool, dark, slightly moist conditions

Culinary uses:
• Tubers are eaten raw in salads — crisp, crunchy, and refreshing with a sweet, nutty flavor
• In French cuisine, braised in butter and herbs as a luxury side dish
• Sautéed, roasted, or fried as a gourmet vegetable
• Used in Japanese tempura and sushi preparations (chorogi)
• Can be pickled in vinegar — a traditional Japanese preparation colored pink with perilla
• Added to soups and stews in the last minutes of cooking to preserve crunch
• Served as a garnish in fine dining restaurants
• In Chinese cuisine, stir-fried with garlic and soy sauce
• The thin skin does not need to be peeled — just wash thoroughly