Kidney fern

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.