Diuris flavescens - critically endangered species listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the terrestrial orchid, Diuris flavescens D.L.Jones as a CRITICALLY ENDANGERED SPECIES in Part 1 of Schedule 1A of the Act, and as a consequence, to omit reference to Diuris flavescens D.L.Jones from Part 1 of Schedule 1 (Endangered species) of the Act. Listing of critically endangered species is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Diuris flavescens D.L.Jones (family Orchidaceae) is a terrestrial herb of the Donkey Orchid genus. It was described in the  Flora of NSW by Jones (1993, p. 144) as follows: “Terrestrial herb. Leaves 2, linear, 8–17 cm long, 3–4 mm wide, conduplicate. Raceme 10–20 cm high, 1–5 flowered. Flowers pale yellow with dark brown markings on the dorsal sepal and labellum, c. 1.2 cm across. Dorsal sepal linear to ovate, 6–9 mm long, 4–5 mm wide, obliquely erect. Lateral sepals linear to oblanceolate, 12–18 mm long, 1.2–1.8 mm wide, deflexed, parallel or crossed. Petals obliquely erect, widely divergent, slightly recurved; lamina elliptic to nearly circular, 6–9 mm long, 4–5 mm wide; claw 4–6 mm long. Labellum 6–8 mm long; lateral lobes linear to more or less ovate, obtuse, often irregular, 2–3 mm long, 0.8–1.2 mm wide; midlobe ovate when flattened, 4.5–6.5 mm wide, ridged along midline; callus of 2 divergent, incurved ridges c. 5 mm long.”

2. Diuris flavescens was first described by Jones (1991) who considered it most closely allied to  D. chrysantha.  Diuris flavescens can be distinguished from  D. chrysantha by having a shorter growth habit with fewer and smaller flowers. The flowers of  D. flavescens are also a paler shade of yellow.

3. Diuris flavescens is endemic to New South Wales where it is known only from the Wingham district from a small number of populations. One confirmed record of the species is from a cemetery, and a second is from private land on the lower Manning River. There are two additional unconfirmed records from nearby (see Copeland 2007). The confirmed populations grow on well-drained loam (Jones 2006) or heavy clay soils (T Fish  in litt. August 2008) in and around remnants of grassy woodland, or sclerophyll forest, in which the groundcover is dominated by  Themeda australis and  Imperata cylindrica (Bishop 2000). Flowering typically occurs during September and October, though may commence in late August. Like most Australian terrestrial orchids the species is believed to be semi-or fully-dependent on a mycorrhizal symbiont.

4. Diuris flavescens is not known to occur in any conservation reserves in New South Wales.

5. Diuris flavescens has a very highly restricted geographic distribution. Depending on the status of unconfirmed records, its area of occupancy is estimated to be 8–12km², based on the number of occupied 2 x 2 km grids (as recommended by IUCN 2006). Its extent of occurrence is estimated to be less than 100km² (Copeland 2007).

6. The total population of Diuris flavescens is estimated to comprise approximately 200 mature individuals, depending on the status of unconfirmed records. The two unconfirmed populations are based on observations of only one or two individuals. Records of the cemetery population have varied from 17 plants to 50 plants based on several surveys of the site during the past 20 years (Copeland 2007, T Fish  in litt. August 2008). As many as 150 plants were observed in the other confirmed population, scattered over an area of approximately 10ha (T Fish  in litt. August 2008).

7. All confirmed and unconfirmed populations of Diuris flavescens occur in the lower Manning River valley, where native vegetation has been severely fragmented by clearing for rural and residential development. The small size of the populations place them at risk of environmental and demographic stochasticity. The cemetery population is frequently visited and may be threatened by trampling as well as illegal orchid collectors. The site is currently managed by a church committee to minimise effects of maintenance activities such as mowing and herbicide spraying, although these have been potential threats in the past. At least one of the unconfirmed populations is threatened by an infestation of  Lantana camara, an introduced shrub that grows in dense thickets that may eliminate ground flora. The largest population may be at risk from development associated with residential subdivision. While building envelopes and roads have been designed to avoid the populations, (T Fish  in litt. August 2008) most plants will be within a few hundred metres of housing and may be exposed to future threats that are typically associated with suburban interfaces, including bushland degradation due to weed invasion, changes in soils, rubbish dumping, trampling and illegal flower-picking. ‘Clearing of native vegetation’ and ‘Invasion, establishment and spread of Lantana ( Lantana camara L.  sens. lat)’ are listed as Key Threatening Processes under the  Threatened Species Conservation Act 1995.

8. Diuris flavescens D.L.Jones  is eligible to be listed as a critically endangered species as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future as determined in accordance with the following criteria as prescribed by the  Threatened Species Conservation Regulation 2002:

Clause 15

The geographic distribution of the species is estimated or inferred to be:

and

Clause 16

The estimated total number of mature individuals of the species is:

and

Professor Lesley Hughes
Chairperson
Scientific Committee

Proposed Gazettal date: 19/12/08
Exhibition period: 19/12/08 - 27/02/09

References

Bishop T (2000) ‘Field Guide to the Orchids of New South Wales and Victoria. 2nd edition’ (University of New South Wales Press: Sydney)

Copeland LM (2007) ‘Conservation status of Diuris flavescens D.L.Jones (Orchidaceae) in New South Wales.’ Report to the NSW Scientific Committee, Sydney.

IUCN (2006) ‘Guidelines for using the IUCN Red List Categories and Criteria. Version 6.2.’ (Standards and Petitions Working Group of the IUCN Species Survival Commission Biodiversity Assessments Sub-committee: Switzerland)

Jones DL (1991) New taxa of Australian Orchidaceae. Australian Orchid Research 2, 1-207.

Jones DL (1993) Diuris. In ‘Flora of New South Wales. Vol. 4’. (Ed. GJ Harden) pp. 138-145 (University of New South Wales Press: Sydney)

Jones DL (2006) ‘A Complete Guide to Native Orchids of Australia including the Island Territories’. (Reed New Holland: Sydney)