The filmy kidney fern (Trichomanes reniforme), also known as Raurenga, is a common sight in North Island and western South Island forests. The translucent kidney-shaped fronds, just a few cells thick, have wavy edges which, when mature, are often lined with tiny spore-producing sporangia. During dry conditions the fronds shrivel up and become almost papery to the touch, but they quickly recover whenever it rains. Kidney ferns commonly form extensive ground mats under forest but also colonise tree trunks and rocks, thriving wherever there is abundant water.
This specimen was found in the dense podocarp forest of the lower Totara Valley, inland of the town of Ross on the South Island West Coast. The area receives upwards of five metres of rain a year, and consequently the forest floor is smothered with thousands of moisture-loving ferns, mosses and lichens of many different species.
The day I spent walking through here was typically dull and rainy, ideal for photographing the lush forest interior where even, subdued light is perfect for revealing every tiny detail. Another burst of rain had just passed through when I found this juvenile kidney fern frond peeking out from under a rotting log in a shallow ravine. A single large raindrop glistened brightly on its lower edge, and the dark shadows immediately behind it made for an effective close-range photograph.
