Nephrolepsis cordifolia

Tuberous Sword Fern Nephrolepidaceae

A handsome, rather indestructible sword fern with a secret weapon beneath the compost: stolons studded with little rounded tubers, produced in such abundance that a mature plant can look as though it has been quietly manufacturing marbles. The erect crown carries bright green, finely divided fronds, each 25–75 cm long and composed of 40–120 pairs of closely set pinnae. The tubers are typically 1–1.5 cm across and are one of the best clues to its identity. 

Widely distributed from the Himalayas and southern China through Japan, Taiwan and tropical Southeast Asia to Australia and the Pacific, with further native populations on islands of the western Indian Ocean and in parts of tropical Africa. It is both terrestrial and epiphytic, occurring from low elevations to around 2800 m, and has become naturalised in numerous warm-temperate and subtropical regions worldwide. 

Cultivate in fertile, humus-rich soil with regular moisture, in partial shade or filtered sun. The tubers act as useful storage organs and also make the plant remarkably good at spreading — give it room unless you enjoy excavating a small crop of fern potatoes every few years.

Nomenclature: first described by Linnaeus in 1753 as Polypodium cordifolium; Carl Presl transferred it to Nephrolepis in 1836 as Nephrolepis cordifolia (L.) C.Presl. The name N. tuberosa and numerous older combinations have been used historically; Nephrolepis cordifolia is the currently accepted name. 

• Hardiness: H4 — -10 to -5°C, with greater protection advisable in prolonged cold
• Height: 45–75 cm
• Spread: 60–100 cm
• Fronds: 25–75 cm
• Tubers: 1–1.5 cm diameter
• Range: Tropical and subtropical Asia to the Pacific, western Indian Ocean and tropical Africa
• Habitat: Terrestrial or epiphytic, from lowland areas to c. 2800 m