Thelymitra sp. 'Adorata' - 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 terrestrial orchid Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined. (Wyong Sun Orchid) as a critically endangered species in Part 1 of Schedule 1A of the Act. Listing of critically endangered species is provided for by Part 2 of the Act.

 

The Scientific Committee has found that:

 

1. Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined. (family Orchidaceae) is a hairless terrestrial herb, dying back annually to a tuberous rootstock. A single linear to linear-lanceolate leaf emerges from the ground in about May, dying off in late November; the leaf is 10-40 cm long, 5-20 mm wide, erect, fleshy, abaxially ribbed, canaliculate, green with a purplish base, sheathing the flowering stem at the base, with an acute apex. The flowering stem (usually emerging in September, with not all plants flowering in all years) is dark bluish-purple when seen from a distance, 20-60 cm tall, 2-5 mm diam. Flowers are fragrant, 2-13 in number, and borne on slender pedicels 1-14 mm long. Individual flowers are 15-27 mm across, pale to dark blue, opening in warm weather. Perianth segments 8-13 mm long, 4-7 mm wide, deep blue, the dorsal sepals, petals, and lateral sepals all ovate to ovate-lanceolate and acute. The labellum is ovate-lanceolate, often narrower than the other segments; the column is erect from the end of the ovary, 5.5-6.5 mm long, 2.5-3.5 mm wide, white to pale blue; the post-anther lobe hoods the anther and is 2.5-3.5 mm long and 1.5-2.5 mm wide, semi-cylindrical and gently curved, dark brownish with a yellow apex, with the distal margin irregularly toothed and with a distinct central notch; auxilliary lobes are absent; the lateral lobes are converging, 1.5-2.0 mm long, fingerlike, obliquely erect, gently curved, each with a terminal tuft of white hairs 1-1.5 mm long. The anther is situated about mid-way along the column, 2-3 mm long, 1.5-2 mm wide, its base partly obscured behind the stigma, the connective produced into a beak 0.4-0.6 mm long. The stigma is situated at the base of the column. Capsules are obovoid, 10-20 mm long, 5-7 mm wide, erect, and ribbed. [Description following J. Jeanes in litt. and Jones 2006: 238; a published illustration is in Jones 2006: 238, as ‘Thelymitra adorata’]. The dark, thick, rigidly erect stems aid field recognition, as compared to other Thelymitra species in the area, even when flowers are closed.

 

2. Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined. is also known as ‘T. adorata Jeanes ined.’ (e.g. Jones 2006), and is referred to as ‘T. adorata ... newly described’ in Fanning et al. (2003) – in fact the species has not yet (at May 2008) been formally named or described.

 

3. Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined. is related and similar to T. aristata Lindl., but the latter occurs south from about Moss Vale (Bishop 2000) and has a flatter, more strap-like post-anther lobe that lacks an obvious apical notch, and has the anther inserted more towards the base of the column and mostly obscured behind the stigma. T. planicola Jeanes is also similar but has the post-anther lobe entire or bilobed only (not multiple-toothed) and not deeply notched at the apex, and with a thin blue collar. T. pauciflora R.Br. and T. angustifolia R.Br. are recorded as co-occurring with Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined., but both differ in having a less robust habit with the leaves less than 10 mm wide (often 6 mm or less), and the post-anther lobe tubular. Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined. is most easily recognised by its relatively large, thick leaf and bracts; its usually deep blue flowers; the post-anther lobe semi-cylindrical, toothed and with a deep central notch and brownish with a yellow apex.

 

4. Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined. is currently known from a few occurrences in the area bounded by the towns of Wyong, Warnervale and Wyongah on the New South Wales Central Coast, within the Wyong Local Government Area and in the Sydney Basin Bioregion (sensu Thackway and Cresswell 1995). The extent of occurrence is about 5 km2 (a range of 5 km east-west by about 1 km north-south). Total area of occupancy is confined to two 4 km2 grids and the recorded populations occupy patches totalling less than 100 m2 within this area. The geographical distribution is therefore very highly restricted.

 

5. Plants occur in small isolated colonies of a few to about 25m2 extent. Flowers are produced in September and October (Branwhite in litt., Jones 2006); not all plants flower every year. Jones (2006) asserts that the species is self-pollinating; J. Jeanes (in litt.) states that ‘the high degree of capsule development would suggest that it is probably autogamous’ [selfing]. Fruits are developed in October and November. Longevity of individual plants, and rate of tuber exhaustion, are unknown. Stems tend very strongly to occur in clumps of three to six arising together from the ground, suggesting either a tendency for seeds to clump, or, more probably, the formation of daughter-tubers, an uncommon but not unknown trait in Thelymitra (P. Weston pers. comm.). Fire response is unknown for this species, but the tubers probably survive low-intensity fires.

 

6. The species occurs from 10-40 m a.s.l. in woodland with grassy understorey in well-drained clay loam or shale derived soils. The vegetation type in which the majority of populations occur (including the largest colony) has been described regionally (Bell 2002) as Dooralong Spotted Gum - Ironbark Forest, with an estimated pre-1760 local extent of about 4736 ha, and a local extent of 2215 ha in 2002, a decline of about 53%. Typical composition of the community, in areas where the orchid is known to occur, is an overstorey of Corymbia maculata and Eucalyptus paniculata, with an open to dense shrub layer of Melaleuca nodosa over a grass/herb ground layer. Bell et al. (2005) note that ‘This vegetation type is highly fragmented within Wyong Shire ... most is in private ownership. Less than 2200 ha of this vegetation type remains within Wyong Shire (Bell 2002)’. B. Branwhite (in litt.) states that the specific habitat of known sites of this Thelymitra involve a correlation of this vegetation type (or its disturbed remnants) with Patonga Claystone, and that this combination is ‘only to be found in a small fraction of the total map unit hectares’.

 

7. Some reports suggest that the species may also occur within the margin of two other vegetation types where these adjoin or constitute portions of the remnant vegetation areas in which the orchid has been recorded. Alluvial Redgum Footslopes Forest (Bell 2002) adjoins Dooralong Spotted Gum - Ironbark Forest at one population, and may constitute habitat for the species. Alluvial Floodplain Shrub Swamp Forest (Bell 2002) also adjoins Dooralong Spotted Gum - Ironbark Forest at one extant population with a report of a small orchid colony on the margin (B. Branwhite pers. comm.), and one apparently extinct population occurred in vegetation probably assignable to this type near Warnervale.

 

8. Bell et al. (2005) document six populations based on data collected in and prior to 2003, with plant numbers ranging from 1-113. To what degree these populations may have been naturally separated prior to recent habitat fragmentation, is unclear. Bell et al. (2005) report that: five of these populations are or were on private property, and one (the largest) is on Wyong Council property. Bell et al. (2005) also state that two populations are extinct (combined total 16 recorded plants), three are ‘potentially extinct’ (combined total of 27 plants) with no plants seen in 2004, and one is extant (170 plants, in eight sub-populations, one of which has been destroyed by earthworks). R. Dickson (in litt.) reports a total of 131 plants found during searches of the total area of occurrence in 2006, but as not all plants flower every year this may not represent a decline between the two surveys. Field inspection of the largest colony in 2007 (R. Makinson in litt. 2007) showed 135 stems present, an increase from the 113 reported for this site in 2003 by Bell et al. (2005), but also confirmed the plant to be absent from a site where eight stems had previously been recorded near Warnervale.

 

9. Threats to the species have been identified by Bell et al. (2005) as including (for all known sites of past and extant occurrence) ‘fragmentation of habitat, increasing urbanisation and associated development, cattle and horse grazing, illegal collecting, and competition from invasive weed species. Five populations previously known are now extinct as a result of some or all of these threats. The largest known population described here is threatened through invasion of weed species such as Whisky Grass (Andropogon virginicus), Cobblers Pegs (Bidens pilosa) and Asparagus Weed (Myrsiphyllum asparagoides), as well as the provision and maintenance of road and services infrastructure.’ R. Dickson (in litt.) identifies a somewhat broader set of threats to the species: ‘illegal collection or destruction of tubers, land clearing, land slashing, invasive weed competition from Lantana camara, Chrysanthemoides monilifera, Whisky Grass (Andropogon virginicus) and Kikuyu (Pennisetum clandestinum), unrestricted ground cover growth ... trail bikes and 4 wheel drive vehicles, hand spraying of herbicides during above ground growth phase (May to late November), land rezoning, housing and industrial development, compression of soil by vehicles, mammals and inappropriate fire regimes ... All threats are considered to be ongoing ... severe reductions leading to extinction are expected to occur within the next 1 year at minimum.’ Possible threats may include; Lantana camara, alteration to natural flows of watercourses, clearing of native vegetation, rabbits, high frequency fires, bitou bush, exotic perennial grasses, soil compression, road verge maintenance and use and encroaching urban development. One site at Warnervale is likely to be subject to a higher frequency of fires than before settlement, although fire frequency at other sites may be likely to decrease as urban boundaries approach.

 

10. ‘Invasion of native plant communities by exotic perennial grasses’, ‘Clearing of native vegetation’, ‘Invasion of native plant communities by Chrysanthemoides monilifera’, ‘Invasion, establishment and spread of Lantana (Lantana camara L. sens. lat.)’, ‘High frequency fire resulting in the disruption of life cycle processes in plants and animals and loss of vegetation structure and composition’ and ‘Invasion and establishment of exotic vines and scramblers’ are listed as Key Threatening Processes under the Threatened Species Conservation Act 1995. ‘Land Clearance’ is listed as a national-level Key Threatening Process under the Environment Protection and Biodiversity Conservation Act 1999.

 

11. Bell et al. (2005) note the tendency of the species to occur in ecotonal situations, whether artificial or natural, and state that ‘It is evident that all populations have taken advantage of additional light generated through minor clearing activities.’ The threshold at which small-scale disturbances become retrograde has not been identified.

 

12. Bell (2002) estimates a 53% local post-settlement decline in the vegetation type (Dooralong Spotted Gum – Ironbark Forest) within which the majority and largest colonies of the species have been recorded, with an estimated 2215 ha remaining in 2002. B. Branwhite (in litt.) asserts further loss of this vegetation type since 2002. Two other vegetation types within which T. sp. ‘Adorata’ may possibly occur, in situations where these adjoin habitat patches dominated by Dooralong Spotted Gum – Ironbark Forest, have also undergone significant declines. Bell (2002) estimates decline of Alluvial Floodplain Shrub Swamp Forest within Wyong Shire as 67.4%, based on estimated extents of 2746.6 ha pre-1750, and 895.4 ha in 2002, and the decline of Alluvial Redgum Footslopes Forest within Wyong Shire as 86.2%, based on estimated extents of 1051 ha pre-1750, and 145.20 ha in 2002. Losses of the vegetation types within which T. sp. ‘Adorata’ occurs or may occur - for all sites except one small colony (4 stems in 2007) near Warnervale (vegetation community undetermined) - therefore range from 53% to 86%. Of the three habitat patches known to support the species, one (Wadalba ridge) is subject to heavy urbanisation and weed infestations in at least part of the planned (Conacher Travers 2006) wildlife corridor reserve; one (also near Wadalba) is subject to heavy disturbance along the ecotones where the orchid tends to occur (e.g. between remnant vegetation and made environments), and one (near Warnervale), is subject to heavy weed infestation and possible increased fire frequency. Declines in the quality of existing habitat are to be expected in the near future unless these processes are mitigated.

 

13. A decline in the number of individual plants of the species is inferred by Bell et al. (2005) for at least two [total 16 plants lost] and possibly up to five [a further 43 plants] of their six populations. Of their total 213 plants (counted between 1998 and Sept 2003) they therefore infer a numerical decline of up to about 20%. Decline in numbers is also asserted by R. Dickson (in litt.) and B. Branwhite (in litt.). Data for the largest colony do not confirm numerical decline, but show a large fluctuation in stem numbers from 113 (2003, Bell et al. 2005) to only 33 stems in 2004 (Bell et al. 2005), and an increase to 135 in 2007 (R. Makinson in litt. 2007); these changes probably reflect drought conditions and non-sprouting of tubers in 2004. There are no data contradicting the assessment of likely local extinction at several other sites made by Bell et al., although one small (4 stems) new colony has been found near Warnervale (R. Makinson in litt. 2007).

 

14. The species is not known to be present in any conservation reserves.

 

15. Thelymitra sp. ‘Adorata’ (B. Branwhite JAJ1030) J. Jeanes ined. 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:

(a) very highly restricted,

and

(d) 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;

(e) the following conditions apply

(i) the population or habitat is observed or inferred to be severely fragmented;

(ii) all or nearly all mature individuals are observed or inferred to occur within a small number of populations or locations.

 

 

Professor Lesley Hughes

Chairperson

Scientific Committee

Proposed Gazettal date: 04/07/08

Exhibition period: 04/07/08 – 29/08/08

References:

 

Bell SAJ (2002) ‘The natural vegetation of the Wyong Local Government Area, Central Coast, New South Wales. Parts 1 and 2. Report to Wyong Shire Council.’ East Coast Flora Survey, Kotara Fair, NSW. In ‘Wyong Conservation Strategy Technical Reports’ (2003, CD-ROM), Wyong Shire Council.

 

Bell S, Branwhite B, Driscoll C (2005) Thelymitra adorata Jeanes ms (Orchidaceae): population size and habitat of a highly restricted terrestrial orchid from the Central Coast of New South Wales. The Orchadian 15: 6-10

 

Bishop T (2000) ‘Field guide to the orchids of New South Wales and Victoria. (2nd edn).’ University of New South Wales Press, Sydney.

 

Conacher Travers (2006). Wadalba Wildlife Corridor Management Plan, September 2006. Conacher Travers [consultants], Kariong NSW.

 

Fanning D, Leonard G, Boggie L, Hargraves F, Lloyd S, Cowdrey A, Leslie J, Branwhite B, Duncan S, Redmond L (2003) ‘Wyong ground orchid survey, Wyong Shire.’ Gunninah Environmental Consultants, Crows Nest NSW. In ‘Wyong Conservation Strategy Technical Reports’ (2003, CD-ROM), Wyong Shire Council.

 

Jones DL (2006) ‘A complete guide to native orchids in Australia including the island territories’. Reed New Holland, Frenchs Forest NSW.

 

Thackway R, Cresswell ID (1995) ‘An interim biogeographic regionalisation for Australia (Version 4.0)’. (Australian Nature Conservation Agency, Canberra).

Page last updated: 28 February 2011