Rhizanthella slateri - endangered population listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list a population of the underground orchid Rhizanthella slateri (Rupp) M.A.Clem. & Cribb in the Great Lakes local government area as an ENDANGERED POPULATION in Part 2 of Schedule 1 of the Act. Listing of endangered populations is provided for by Part 2 of the Act.

The Scientific Committee has found that:

1. Rhizanthella slateri (Rupp) M.A.Clem. & Cribb (family Orchidaceae) is not currently listed as an endangered species in Part 1 of Schedule 1 or a critically endangered species in Part 1 of Schedule 1A and as a consequence populations of this species are eligible to be listed as endangered populations. Rhizanthella slateri is currently listed as a Vulnerable Species in Part 1 of Schedule 2 of the Act.

2. Rhizanthella slateri (Rupp) M.A.Clem. & Cribb is an endemic Australian orchid that has been described by Bernhardt (1993) as follows: "Terrestrial saprophytic herb with fleshy underground stem to 15 cm long and 15 mm diam., whitish, often branching, with prominent, fleshy, overlapping bracts. Flower heads maturing below the soil surface or extending 2 cm above the ground, to c. 2 cm diam., the receptacle of up to 18 whitish triangular bracts to 8 mm long; flowers up to 30, tubular and purplish. Dorsal sepal curved, the tip narrowing linear to filiform, the base broad and hooding the column and most of the 2 lateral petals; lateral sepals erect, broad at the base but each lateral sepal folding lengthwise into a filiform tip longer than the dorsal sepal and often protruding beyond the length of bracts making up the cup. Lateral petals about half the length of the lateral sepals. Labellum claw a short, flexible hinge; labellum lamina cordate, thick, tongue-like with the upper surface covered with fine papillae. Column short and broad with column wings reduced to narrow, papillose 'ears'; anther broad and curving, stigma a thickened pad. Flowers Oct.-Nov."

3. Biologically, Rhizanthella slateri is of significant conservation value because of its unusual life history. It is one of only three Australian species, and a small number of species worldwide, that are capable of completing their entire lifecycle underground (Jones 1988). While a number of mycoheterotrophic plant species remain subterranean for most of their lives, almost all of these emerge to flower and fruit. Subterranean flowering plants such as these are extremely unusual and are of great scientific interest to biologists all over the world.

4. Rhizanthella slateri is restricted to New South Wales where it is currently known from fewer than 10 locations including Bulahdelah, the Watagan Mountains, the Blue Mountains, Wiseman's Ferry area, Agnes Banks and near Nowra. A further population from the Lamington Plateau in Queensland, previously regarded as Rhizanthella slateri, is now recognised as a new, as yet unnamed, species of Rhizanthella (D.L. Jones, pers. comm.). The Rhizanthella slateri population in the Great Lakes local government area occurs at the known northern limit of the species' range and is disjunct from other known populations of the species. It also represents the Type locality, where the species was first discovered in 1931 (Jones 1988).

5. Surveys conducted between 2002 to 2005 identified approximately 75 flowerheads at a site within the Great Lakes local government area, more than ten times the number observed at any other site. The Rhizanthella slateri population in the Great Lakes local government area is thus likely to be the largest and most extensive known population of the species. Other known populations of Rhizanthella slateri are fragmented and highly disjunct, comprising isolated individuals or small clusters of plants. Some of these have been discovered destructively, during the course of construction works (Jones 1988). Due to the cryptic growth form of the species, it is likely that some populations have been destroyed before they were discovered, and that currently unknown populations may be destroyed in the future before they are discovered. The known population near Bulahdelah is therefore of critical importance to the species' conservation.

6. The Rhizanthella slateri population in the Great Lakes local government area is threatened by a proposal to construct a road through the population. The proposal will result in direct removal of 4% of the known population (Roads and Traffic Authority 2004) and other individuals as yet undetected may become exposed after clearing or excavation works. A further 34% of the known population is indirectly threatened by altered drainage and changes in soil moisture (Roads and Traffic Authority 2004), and by weed invasion associated with the road. The proposed road will remove 9% of known habitat and 29% of potential habitat for the species, fragmenting the population and potentially disrupting pollination and seed dispersal (Roads and Traffic Authority 2004). Orchid collectors represent a further threat to the species due to its very unusual growth form and extreme rarity, and the publicity associated with the Bulahdelah site. The Rhizanthella slateri population in the Great Lakes local government area may also be threatened by environmental and demographic stochasticity due to its restricted area and small size. These threats represent a continuing decline in the population of Rhizanthella slateri in the Great Lakes local government area.

7. The population of the Rhizanthella slateri (Rupp) M.A.Clem. & Cribb in the Great Lakes local government area is eligible to be listed as an endangered population as, in the opinion of the Scientific Committee it is facing a very high risk of extinction in New South Wales in the near future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

Clause 19

    (a) it is disjunct or near the limit of its geographic range

    (c) it is otherwise of significant conservation value

        Clause 21

        The geographic distribution of the population is estimated or inferred to be highly restricted and:

          (a) a projected or continuing decline is observed, estimated or inferred in:
          (i) an index of abundance appropriate to the taxon

          (ii) geographic distribution, habitat quality or diversity, or genetic diversity


        Clause 22

        The estimated total number of mature individuals in the population is low, and:

        (a) a projected or continuing decline is observed, estimated or inferred in:

          (i) an index of abundance appropriate to the taxon

          (ii) geographic distribution, habitat quality or diversity, or genetic diversity


        Clause 23

        The estimated total number of mature individuals of the population is observed, estimated or inferred to be very low.

        Associate Professor Lesley Hughes

        Chairperson

        Scientific Committee

        Proposed Gazettal date: 08/12/06

        Exhibition period: 08/12/06 - 09/02/07

        References:

        Bernhardt P (1993) Rhizanthella. Pp 219 in: G. Harden (ed.) 'Flora of New South Wales. Volume 4'. (New South Wales University Press: Kensington.)

        Jones DL (1988) Native orchids of Australia. (Reed: Sydney.)

        Roads and Traffic Authority (2004) Bulahdelah Upgrading the Pacific Highway, Environmental Impact Statement. Technical Paper 7, Ecological Assessment and Species Impact Statement. Roads and Traffic Authority of NSW.

      More information



      Page last updated: 28 February 2011