Caladenia arenaria Fitzg. Recovery Plan

Threatened Species Unit, Western
The State of New South Wales, Department of Environment and Conservation, 2004
ISBN: 0731365399

1 Current conservation status

Caladenia arenaria is listed on Schedule 1 (endangered) of the NSW Threatened Species Conservation Act, 1995 (TSC Act, 1995), and on Part 1 (endangered) of the Environmental Protection and Biodiversity Conservation (EPBC) Act 1999. The species is known from five locations, with a total population of around 2,000 individuals. Under the modified IUCN criteria of Keith et al. (1997) the species is ranked as endangered due to the restricted number of populations, small total area occupied, limited capacity to regenerate after a decline, and occurrence outside conservation reserves.

2 Description

Caladenia arenaria is a tuberous, summer-deciduous perennial herb of the spider caladenia group. A single hairy leaf up to 15 cm long emerges from the ground in autumn or early winter from the tuber, with the flower stem appearing later from the centre of the leaf. Usually one, but occasionally two flowers are produced on a stem from c. 10 30cm high. The flowers are large, with the individual floral segments (tepals) being up to 6 cm long. The segments are white to pale yellow, narrow, and taper to fine maroon tips (the colour being conferred by crimson glandular hairs). The labellum (lip) is of a similar colour to the tepals but the tip is often marked with crimson. Flowering occurs from late August until early October. If fertilised the ovary develops into a capsule, and after a maturation of 3-4 weeks the seeds are released as the capsule dries. The above ground parts wither and die, and the plant persists underground as a tuber over summer and early autumn.

Caladenia arenaria is potentially a very long-lived perennial herb. At the commencement of growth before the winter spring growing season the more or less spherical summer dormant tuber (mother tuber) produces a new tuber (daughter tuber) which matures in spring at the end of the growing season. By this stage the mother tuber is exhausted and dies. In this way the whole plant is renewed annually and theoretically has somatic immortality. Reproduction in C. arenaria is almost exclusively by seed; vegetative production (occurring with the production of two rather than one daughter tuber) is very rare.

Plants are self fertile (ie. able to produce seed if pollen is transferred to the stigma of the same individual) but most seed production is believed to be the result of outcrossing (pollen transfer between different plants). Seeds are extremely small and without nutrient stores; they are believed to have a short longevity (perhaps one or two seasons only).

Caladenia arenaria has been beautifully illustrated by Fitzgerald (1882) and also by Bernhardt (1993) and Bishop (1996).

3 Distribution & abundance

Caladenia arenaria was described by Fitzgerald in 1882 from the "Edwards, Murrumbidgee, Yanco and Columbo Rivers, growing on the sand-hills among pines" (Fitzgerald 1882). Collections cited by Fitzgerald in the 1880s were from Deniliquin Station, Bethungra and Murrumburra. The linear distance between Deniliquin and Bethungra is about 330 km. Other collections determined as C. arenaria from the 1880s were from Yass and just north of Mudgee. If these specimens (particularly the specimen from Mudgee which appears to be an outlier by approximately 250 km) are C. arenaria, the range of the species exceeded 500 km.

The species was rediscovered in 1983 on a roadside north of Narrandera. In 1996 the species was found on private property near Urana, and survey in 1998, 1999 and 2000 has revealed three other populations on State Forest in the Riverina (G. Robertson unpubl. data; Carr 2000, 2001). Two of these populations in State Forest account for the bulk of the total known population. In Lonesome Pine State Forest there are an estimated 1,000+ individuals growing in about 5 ha. In Buckingbong State Forest over 200 were counted in about 50 ha of forest, but the plants are scattered. Total size of the populations or sub-populations is not known. In Yarranjerry State Forest the numbers are not known. The distance between the northernmost and southernmost populations is around 150 km. The estimated population numbers and area occupied by each population are given below:

Location Roadside Urana Yarranjerry Buckingbong Lonesome Pine
Population size 20 300 40+ 500+ 1000+
Area of population (ha.) 0.5 12.5 60 45.6 5.1

There are reports that may be attributable to C. arenaria at two other locations in the south western slopes and Riverina. These locations were surveyed in 1999 and 2000, but no plants were found despite precise location data. In 2000 at one of these locations a hybrid (one plant) considered to be C. arenaria x C. callitrophila (another Riverina endemic) was found. At the other location an experienced orchidologist found a plant in 1996. Both sites show evidence of heavy grazing pressure and weed invasion and it is possible that populations are extinct.

The species has suffered a massive contraction in range and abundance in the last century, given the documented historic range and variety of habitat in which the species now occurs. There do not appear to have been any specimens lodged at herbaria between the collections in the 1800s and 1983, when the species was found north of Narrandera.