Arisaema thunbergii

Arisaema thunbergii is a woodland perennial in the arum family, Araceae. Gardeners also know it as cobra lily. Kew places its native range in Japan and South Korea. Plants For A Future also lists eastern and northern Taiwan. It grows in Japanese forests and rests as an underground tuber. Its leaves and flowers rise above ground during the growing season.

Plants reach 1–2 feet [0.30–0.61 metres] tall in gardens. They can spread to 2 feet [0.61 metres] across. A single leaf sits flat above the stem. It divides into 9–17 slim, lance-shaped leaflets. One flower structure appears near the base of the leaf stalk. The bloom season runs from April through May. A white, pitcher-shaped spathe bears purple spots arranged in stripes. Its pointed hood ranges from dark purple to almost black. The hood bends forward over the opening below. This shape gives the plant its cobra lily name. Missouri Botanical Garden lists both flowers and fruit as showy.

Grow this plant in shade with rich, humus-filled soil. Missouri Botanical Garden allows partial shade through full shade. Plants For A Future favours dappled shade rather than deep shade. Keep the soil moist, but let excess water drain. Heavy clay does not suit it well. Set the tubers 3–4 inches [0.08–0.10 metres] below the soil surface. Missouri Botanical Garden lists USDA zones 5–9 in its summary. Its care notes give a narrower range of 5, perhaps 6, through 8. A sheltered site helps in the St. Louis area.

Groups suit shady woodland beds and informal wild gardens. Leave settled plants undisturbed where possible. Missouri Botanical Garden also suggests rain gardens as a use. It reports no major insect or disease problems. Plants grown from seed may need three to five years to flower. Plants For A Future advises sowing fresh seed in a shaded cold frame. Stored seed may need a cold period before germination. Tubers can be divided after growth dies down in late summer.

Plants For A Future records no known food use. The plant contains calcium oxalate crystals that cause sharp mouth and tongue pain when eaten. That source records medicinal uses of the root, including use for wounds and to promote urination. These records do not establish safe home use. It lists no other practical uses and does not flag weed potential.