Zieria buxijugum - critically endangered species listing

NSW Scientific Committee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the shrub Zieria buxijugum J.D. Briggs & J.A. Armstr. as a CRITICALLY ENDANGERED SPECIES in Part 1 of Schedule 1A of the Act, and as a consequence, to omit reference to Zieria buxijugum J. D. Briggs & J.A. Armstrong from Part 1 of Schedule 1 (Endangered species). Listing of Critically Endangered species is provided for by Part 2 of the Act.


The Scientific Committee has found that:


1. Zieria buxijugum (family Rutaceae) is described by Armstrong (2002) as an “erect shrub up to 3.5 m; young branches terete, densely tuberculate and covered with a velvety indumentum of short stellate hairs throughout; older branches less conspicuously tuberculate, glabrescent. Leaves palmately trifoliolate, opposite, petiolate. Petiole 2.0-5.0 mm long, tuberculate, pubescent all over with a dense velvety indumentum of very short stellate hairs. Central leaflet linear to narrow oblanceolate (7.0) 15.0-28.0 (41.0) x (1.5) 2.0-3.0 (4.0) mm, dull grey-green above, pale green below; upper surface tuberculate, with a fine velvety indumentum of very short stellate hairs, midrib conspicuously sunken, lateral veins slightly sunken; under surface tuberculate, with a dense velvety indumentation of short stellate hairs; apex obtuse; margin entire, recurved; primary vein prominent on under surface, densely stellate-pubescent, with numerous tubercles; secondary venation slightly raised but largely obscured on under surface. Secondary leaflets similar to central leaflet but smaller, usually 0.6-0.8 times as long. Inflorescence an axillary cyme, as long as or longer than the leaves (2) 10-16 (28)-flowered. Peduncle (3) 4-10 (15) mm long, densely tuberculate, densely pubescent with short stellate hairs. Bracts persistent (2 bracts are present on the peduncles of juvenile inflorescences, only one bract or bracteole is present at each node in mature inflorescences), linear to oblanceolate, 1.0-5.0 x 0.5-1.0 mm, sparsely tuberculate. Pedicel terete, 1.0-1.5 mm long, not tuberculate, densely stellate hairy, subtended at the base by a pair of minute bracts. Flowers white, moderately conspicuous, 6.0-7.0 mm diameter. Calyx lobes deltoid, 0.8-1.0 x 0.6-0.8 mm, very much shorter than the petals, tuberculate, hirsute adaxially, densely pubescent abaxially with very short stellate hairs. Petals imbricate in bud, ovate-elliptic to broad oblanceolate, 3.5-4.0 x 1.5-2.0 mm, with a very small inflexed acuminate tip; adaxial surface moderately to sparsely stellate-pubescent; abaxial surface tuberculate, densely stellate-pubescent, Stamens not persisting in the fruiting stage; filaments 0.8-1.0 mm long, glabrous, not tuberculate; anthers 0.4 x 0.4 mm, not apiculate, attached in the lower third, orange-red in colour (cream in dry state). Disc interrupted and distinct, glabrous, white. Ovary dotted with pellucid oil glands, glabrescent. Stigma 0.3 mm broad, 4-1obed. Fruit red-brown when young, becoming green-brown to green at maturity, densely tuberculate (i.e. glands obvious on carpel surface), with sparsely scattered stellate hairs when young, becoming glabrescent at maturity. Cocci lacking an appendage. Seed dark brown to dark grey-brown, striate, 1.8-2.0 x 1.0-1.3 mm; covering to the raphe shiny black and striate, not smooth, Seed surface: ridges well-developed but flattened; branches and cross-ridges not common; wax absent. Elaiosome 2.0 x 0.8 mm.”


2. Zieria buxijugum was first discovered in 1986. The species has been known by a number of informal names, including ‘Z. buxijugum J. D. Briggs & J. A. Armstr. ms (Parris 9079)’ (Armstrong & Harden 2002), ‘Z. sp. G’ (Armstrong 1991), ‘Z. sp. 14’ (Briggs & Leigh 1988) and ‘Z. sp. P (Box Range North)’ (J.D. Briggs pers. comm. 2008). Zieria buxijugum is closely related to Z. formosa, from which it is distinguished by the absence of small terminal appendages on its anthers and narrower leaflets (2-3 mm wide cf. 3-5 mm wide in Z. formosa).


3. Zieria buxijugum is endemic to New South Wales and known only from the Pambula area on the far south coast of NSW. This species occurs in shrubby heath vegetation growing in skeletal brown loam, on an ignimbrite rock outcrop. Plants flower in September and are likely to be pollinated by insects. The fire response of Zieria buxijugum is unknown, however many species of Zieria are killed by fire.


4. Zieria buxijugum has a very highly restricted geographic distribution. The species is known from only one locality within a total extent of occurrence and area of occupancy of less than 4 km2, based on 2 x 2 km grid cells, the scale recommended for assessing areas of occupancy by IUCN (2008). Other surveys and searches in and around the area failed to locate any additional populations (Briggs & Leigh 1990; NSW NPWS 2002; J.D. Briggs pers. comm. 2008).


5. The total population of Z. buxijugum contains an extremely low number of mature individuals. When last surveyed in October 2002, there were six mature plants and a further 74 smaller plants at the site (J.D. Briggs pers. comm. 2008).


6. The population of Z. buxijugum has undergone a very large reduction in recent years. When first surveyed in 1987, 68 mature plants were recorded in the population (Briggs & Leigh 1990). By 1999, the number of mature plants had increased to 121 (NPWS 2002). Between 1999 and 2002 the number of mature plants in the population had declined by 95%, probably as a result of drought and browsing by wallabies (NSW NPWS 2002, J.D. Briggs pers. comm. 2008). To reduce browsing, ten wire-mesh guards were constructed around selected plants in 2002. However the population has not been surveyed since 2002 and the guards have never been inspected to determine whether they remain an effective barrier against further browsing (J.D. Briggs pers. comm. 2008).


7. The very small number of individuals and their distribution as isolated individuals at a single location makes Z. buxijugum highly susceptible to stochastic events including wildfire, damage associated with human access, disease, extreme weather events or severe drought. The species has been threatened by severe browsing from swamp wallabies in the recent past, and browsing may periodically threaten the species in future. Given the risks associated with the known impact of browsing on the population, the uncertain security of the mesh guards, and the uncertain management practices that may accompany future changes in ownership, the species is projected to undergo a future decline. Increasing frequency and intensity of drought (Hennessy et al. 2004) in the future may further threaten the species. ‘Anthropogenic Climate Change’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.


8. Zieria buxijugum occurs exclusively on private land and is not known to occur in any conservation reserves in New South Wales.


9. Zieria buxijugum J.D. Briggs & J.A. Armstr. 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 14

The species has undergone, is observed, estimated, inferred or reasonably suspected to have undergone, or is likely to undergo within a time frame appropriate to the life cycle and habitat characteristics of the taxon:

(a) a very large reduction in population size

based on:

(d) an index of abundance appropriate to the taxon.


Clause 15

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

(a) very highly restricted,


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

(i) an index of abundance appropriate to the taxon.


Clause 16

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

(a) very low,


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

(i) an index of abundance appropriate to the taxon.


Clause 17

The total number of mature individuals of the species is observed, estimated or inferred to be:

(a) extremely low.


Dr Richard Major


Scientific Committee


Proposed Gazettal date: 31/07/09

Exhibition period: 31/07/09 - 25/09/09




Armstrong JA (1991) Zieria. In ‘Flora of New South Wales. Volume 2’ (Ed. G.J. Harden). (University of New South Wales Press: Kensington).


Armstrong JA (2002) Zieria (Rutaceae): a systematic and evolutionary study. Australian Systematic Botany. 15, 277-463.


Armstrong JA, Harden GJ (2002) Zieria. In ‘Flora of New South Wales. Volume 2’. Revised edition (Ed. GJ Harden). (University of New South Wales Press: Kensington).


Briggs JD, Leigh JH (1988) Rare or threatened plants: 1988 revised edition. Australian National Parks and Wildlife Service Special Publication No. 14, Canberra.


Briggs JD, Leigh JH (1990) Delineation of Important Habitats of Threatened Plant Species in South-Eastern New South Wales. Australian Heritage Commission, Canberra.


Hennessy K, McInnes K, Abbs D, Jones R, Bathols J, Suppiah R, Ricketts J, Rafter T, Collins D, Jones D (2004) ‘Climate change in New South Wales. Part 2: Projected change in climate extremes.’ (CSIRO: Melbourne).


IUCN (2008) ‘Guidelines for using the IUCN Red List Categories and Criteria. Version 7.0.’ (Standards and Petitions Working Group of the IUCN Species Survival Commission Biodiversity Assessments Sub-committee: Switzerland)


NSW NPWS (2002) Draft Recovery Plan for Zieria formosa, Zieria buxijugum and Zieria parrisiae. NSW National Parks and Wildlife Service, Hurstville NSW.

Page last updated: 28 February 2011