Common Name: cave fern
Scientific name: Tectaria devexa var. devexa
Conservation status: Tectaria devexa var. devexa is Endangered in Queensland (Queensland Nature Conservation Act 1992) and is considered a low priority for conservation under the Department of Environment and Heritage Protection 'Back on Track' species prioritisation framework.
The cave fern (Tectaria devexa var. devexa) is a small, tufted, terrestrial fern with pale green fronds.
Habitat and distribution
The cave fern grows in thin pockets of soil on the walls and floor near the entrance to limestone caves in situations where sufficient natural light and moisture are available to support plant growth. Mature plants produce microscopic spores that spread over the surrounding cave surface and which germinate during moist conditions. The moisture required to sustain cave ferns is largely from seepage that occurs after periods of heavy rainfall.
The cave fern is widely distributed on limestone in Sri Lanka, parts of Southeast Asia and Vanuatu. Within Australia, the cave fern is known from just two places in The Caves district, 25 km north of the central Queensland city of Rockhampton. The occurrences in central Queensland are significant being separated from closest populations by thousands of kilometres. They can be considered as relic populations that have survived in isolated pockets of suitable habitat for hundreds of thousands of years.
The cave fern was first collected by botanists from Capricorn Caves, one of the two known Australian sites, in 1945 where plants reportedly covered large sections of the cavern walls. A small second population was discovered at a cave entrance at nearby Mt Etna National Park in 2001.
There is anecdotal information that around the time of European settlement the cave fern may have been more widespread around The Caves.
The limestone caves and associated vine thickets north of Rockhampton support a number of species of special conservation interest in addition to cave fern. Examples are the ghost bat (Macrcodema gigas) and the shrub scarlet fuchsia (Graptophyllum excelsum).
A survey in the mid-1990’s highlighted that the cave fern population at Capricorn Caves was in decline. A total of just 39 adult and sub-adult plants were observed. Ten years later, the number of plants had dwindled further to 21 at six different locations within the cave system.
When discovered in 2001, the nearby population at Mt Etna Caves comprised just four adult plants and 5-6 juveniles and over time the health of these ferns was also observed to decline.
The reduction in the number of cave ferns at both sites has been largely attributed to prolonged dry periods associated with drought.
An innovative project to recover the cave fern was initiated in 2006 by Greening Australia in partnership with Capricorn Caves, the Queensland Herbarium, Heaton’s Fern Nursery, Griffith University and The Society for Growing Australian Plants. The project was funded through the WWF Threatened Species Network.
The project pioneered the propagation of cave fern with hundreds of young plants successfully raised from spores collected from mature surviving plants. Hand-raised ferns have been planted out into suitable micro-sites at Capricorn Caves. Many of the cave ferns have survived, however they are vulnerable to changes in weather and will wilt in prolonged periods of hot weather. While the fronds may appear dead, it has been found that the rhizome (roots) can remain dormant for 6-8 weeks. They recover after rain and soon grow new fronds. A watering system has been installed to help the ferns survive dry periods.
Prolonged dry weather isn’t the only obstacle that cave fern endures. It is eaten by native rock wallabies and scrub turkeys will uproot the fern searching for bugs among the rhizomes.
Another experiment in progress at Capricorn Caves involves trial germination. The fronds from the existing ferns are pruned regularly and used to distribute spores within cave entrances. Other fronds have been placed on seedling trays in fish tanks. The spores need a moist environment to germinate; therefore, naturally, the fern will only reproduce in the wetter months. The fish tank acts as a ‘humidicrib’, keeping soil and spores moist until germination occurs. If these trials are successful, the cave fern will be germinated on-site and introduced back into the caves, to ensure the continued survival of the species in Australia.
Butz M. 2004. National Recovery Plan for Tectaria devexa. Department of the Environment and Heritage, Canberra.