Kidney fern

Hymenophyllum nephrophyllum

Hymenophyllum nephrophyllum is a fern distinctive for its undivided, kidney-shaped fronds, which give the plant its English common name, the kidney fern. The fronds, or laminae, are 3–10 cm by 4–13 cm and are a shiny, translucent green. The translucent nature of the kidney fern’s fronds is due to them being very thin, only one cell thick as a sporeling, which increases to 3-4 cells when the plant reaches maturity. The fronds are supported on brittle stipes 5–25 cm in length. Mature plants have a row of sori (a collection of sporangia) crowning the upper margin of their frond, where they resemble a row of small brown pegs. A feature Hymenophyllum nephrophyllum shares with some other filmy ferns is the ability to curl up tightly during dry conditions in order to reduce moisture loss; this gives kidney fern one of its Māori common names, kopakopa (to wrap or clasp). After rain or when conditions improve, it unfurls and recovers.
SpeciesHymenophyllum nephrophyllum
Photographed in
New Zealand