Arisaema costatum

Arisaema costatum, the ribbed cobra lily, belongs to the Araceae family. Its native range runs from the Himalaya to southern Tibet. This tuberous perennial grows in cool, wet woods and on cliffs. It also occurs among shrubs and in grassland within forest areas. Wild plants can form large colonies. Its leaves die back each year, leaving the tuber below ground.

The RHS describes plants around 2 feet [0.6 m] tall. Its listed garden range reaches 1.6–3.3 feet [0.5–1 m] in height and spread. Plants may take five to ten years to reach full size. The large, glossy leaves have three lobes and deep green blades. Each leaf can reach about 1.3 feet [0.4 m] long. Raised veins give the leaves a ribbed look. Purple edges add a clear contrast to the green blades.

Leaves appear in early summer, before the flowers open. The flower display then lasts through summer. A deep purple spathe forms a hood marked with white stripes. A long, thin, twisted spadix adds to its unusual shape. The bold leaves and hooded blooms suit a shaded woodland bed. The RHS also lists borders, containers, and planting beneath shrubs as uses. Its upright form can fit small courtyard and informal gardens.

Give this plant a cool, sheltered spot with partial shade. It needs humus-rich soil that holds moisture but drains well. Loam or sandy soil suits it, with acid or neutral pH. Plant tubers about 0.7 feet [0.2 m] deep in winter or spring. Keep dormant tubers from drying out, but avoid waterlogged winter soil. Leaf mould mulch can help protect them in colder places. The RHS rates it H4; PFAF lists USDA zones 6–9. It needs no pruning. Sow seed in a cold frame in autumn or spring. Remove offsets in late summer to raise more plants.

Slugs and vine weevil may cause trouble, though disease is uncommon. The plant harms people and pets if eaten. It can also irritate skin and eyes; wear gloves when handling it. PFAF records food use of the root after cooking and drying. It also warns that calcium oxalate crystals cause sharp mouth pain. These food records do not make raw plant parts safe. PFAF records no known medicinal or other uses.