NSW Scientific Committee - final determination
The Scientific Committee has found that:
1. Prostanthera marifolia R. Br. (family Lamiaceae) was first described in 1810, and was subsequently collected during the 1800s and early 1900s from around Middle Harbour in northern Sydney. Early records from south of Sydney and the south coast that were previously ascribed to this species have since been identified as Prostanthera densa. Due to an absence of records over a number of decades, Prostanthera marifolia was presumed to be extinct until it was recently rediscovered in the Manly area of northern Sydney.
2. Prostanthera marifolia R. Br. has recently been characterised by (B Conn in litt.) as an ‘erect, openly branched shrub up to c. 0.3 m high; faintly aromatic. Branches subterete, sparsely to moderately hairy [16–20 hairs/mm2]; hairs ± straight, spreading or slightly retrorse, c. 0.3–0.6 mm long, white; sparsely glandular [up to 6 glands/mm2]. Leaves green, faintly aromatic (when crushed), sparsely to moderately hairy [as for branches]; sparsely glandular [as for branches]; petiole 0.5–1 mm long; lamina ovate to almost elliptic, 8–12(-15) mm long, 4–6(-8) mm wide [length to width ratio 1.7–2.2, length of maximum width from base to total lamina length ratio 4–6]; base shortly attenuate; margin entire or occasionally slightly 1-lobed on each side, rarely with one additional lobe, may appear bluntly 1-toothed on each side because margin slightly recurved; apex rounded; venation not visible, except midrib raised on lower surface. Inflorescence a frondose racemiform conflorescence, uniflorescence monadic; 2–8(-12)-flowered [per conflorescence]. Pherophylls absent. Podium 1–1.5(-2.3) mm long, sparsely to moderately hairy [as for branches], sparsely glandular [as for branches]. Prophylls inserted near middle or on distal half of podium [a1 axis to anthopodium ratio 1.2–1.9], opposite, narrowly elliptic to narrowly obovate, 1–1.5 mm long, c. 0.2 mm wide [length to width ratio 5–8, length of maximum width from base to total lamina length ratio 0.6–0.9], with long spreading hairs [as for branches]; base attenuate or truncate to very slightly broader; margin entire; apex obtuse. Calyx light green, with mauve-purple tinge adaxially; outer surface sparsely to moderately hairy [10–18 hairs/mm2], hairs spreading, 0.4–0.8 mm long; sparsely to moderately glandular [10–15 glands/mm2]; tube 1.3–1.8(-2) mm long; abaxial lobe very broadly ovate, 2.5–3.8 mm long, 2.2–3.2 mm wide [length to width ratio 1.1–1.2], apex obtuse to rounded; adaxial lobe very broadly ovate, 2.5–3.6 mm long, 2.5–3 mm wide [length to width ratio 1–1.2] apex obtuse [adaxial lobe length to abaxial lobe length ratio 0.9–1]. Corolla (9-)10–15 mm long, purple, white on inner abaxial surface of tube; outer surface sparsely to moderately hairy [10–30 hairs/mm2], sparsely glandular [10–16 glands/mm2]; inner surface sparsely to moderately hairy (similar to outer surface); tube (5-)6–8 mm long; abaxial median lobes very broadly obovate or spathulate, 8–10(-12) mm long, 6–7(-9) mm wide [length to width ratio 0.9–1.2], apex bilobed (sinus 1.8–3 mm long, 2–3 mm wide distally); lateral lobes obovate to slightly oblong, 6–8(-9) mm long, 4–6 mm wide [length to width ratio 1–1.5], apex slightly undulate, obtuse; adaxial median lobe-pair depressed ovate, 3–4(-4.5) mm long, 6.5–8(-9) mm wide [length to width ratio 0.4–0.5], deeply bilobed (sinus c. 3 mm long), apex of each lobe rounded. Stamens inserted 1.5–2 mm above base of corolla; filaments 3–3.5 mm long, glabrous; anthers 0.8–1 mm long, lobes slightly cristate on basal dorsal surface (trichomes narrowly triangular, c. 0.1 mm long), lobes with basal acumen to 0.1–0.2 mm long, connective extended to form basal appendages 0.6–0.9 mm long, terminating in a few triangular trichomes c. 0.1 mm long. Disc ± cylindrical, 0.2–0.3 mm long. Pistil 6–8 mm long; ovary cylindrical to obovoid, 0.4–0.5 mm long, diameter at base 0.3–0.4 mm, lobes 0.1–0.2 mm long, glabrous; style 6–7 mm long; stigma lobes 0.3–0.4 mm long. Fruiting calyx not to very slightly enlarged (abaxial lobe 3.5–3.8 mm long, c. 3.5 mm wide [length to width ratio 1–1.1]; adaxial lobe 3.5–3.7 mm long, c. 3.5 mm wide [length to width ratio 1–1.1]; [adaxial lobe length to abaxial lobe length ratio c. 1]). Mericarps 1.5–1.8 mm long, distally c. 0.5 mm extended beyond base of style, distal diameter c. 1 mm; seeds slightly obovoid-cylindrical, c. 1 mm long, 0.5–0.7 mm diameter.’
3. Prostanthera marifolia is currently only known from the northern Sydney suburb of Seaforth and has a very highly restricted distribution within the Sydney Basin Bioregion (sensu Thackway and Cresswell 1995). The single population is fragmented by urbanisation into three small sites. All known sites are within an area of 2x2 km. Two of the sites are within the local government area of Manly and one site is in the LGA of Warringah.
4. Records of Prostanthera species from Cronulla, Waterfall, Helensburgh, Jervis Bay and Nelsons Bay that were previously determined as P.marifolia have been recently assigned to other taxa, mainly P. densa (B.Conn, National Herbarium of NSW, pers. comm.), which is currently listed as a Vulnerable species under the Threatened Species Conservation Act 1995. Prostanthera marifolia is also thought to be closely related to P. junonis (B. Conn, pers. comm.), a species from the Gosford district listed as Endangered under the Threatened Species Conservation Act 1995.
5. Prostanthera marifolia plants occur as localised patches in or in close proximity to the Duffys Forest Ecological Community, which is listed as an Endangered Ecological Community in Schedule 1, Part 3 of the Threatened Species Conservation Act 1995. The sites are located on deeply weathered clay-loam soils associated with ironstone and scattered shale lenses, a soil type which only occurs on ridge tops and has been extensively urbanised.
6. The population comprises a very low number of individuals (approximately 90-130 when the sites were surveyed in 2005). The one site in Garigal National Park has currently only one known standing plant, although a persistent seed bank may be present in the soil. Most individuals occur in the largest site that contains 76-83% of the total population. The response of P. marifolia to fire is currently not known (B. Conn pers. comm.). Fire history maps show there were major fires in the area in 2000/01 and 1990/91, however due to the fragmented landscape, they may not necessarily have burnt the highly restricted sites where P. marifolia occurs.
7. Prostanthera marifolia is threatened by habitat loss due to small-scale clearing. One site is adjacent to a main arterial road, and consequently is vulnerable to road widening and maintenance activities, as well as future housing development. A second site is adjacent to a golfcourse, and may be threatened by maintenance activities. The third and smallest site is protected from clearing within Garigal National Park, but is located very close to the Park boundary near an existing cleared area. ‘Clearing of native vegetation’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.
8. As a consequence of habitat fragmentation and edge effects from adjacent urban land uses, all three known sites of Prostanthera marifolia are threatened by habitat degradation processes that are commonly associated with urban interfaces. These include urban stormwater run-off and seepage, fertiliser and herbicide drift, weed invasion, excessive human traffic and rubbish dumping. Inappropriate fire regimes and infection by soil pathogens may also pose threats, depending on the response of the species. 'High frequency fire resulting in the disruption of life cycle processes in plants and animals and loss of vegetation structure and composition' and ‘Infection of native plants by Phytophthora cinnamomi’ are listed as Key Threatening Processes under the NSW Threatened Species Conservation Act 1995.
9. Prostanthera marifolia is threatened by environmental and demographic stochasticity due to its very highly restricted distribution and small population size. As a result of the above mentioned threats, Prostanthera marifolia is at risk of a projected decline in abundance, geographic distribution or habitat quality.
10. Prostanthera marifolia R. Br 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:
(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.
Clause 16
The estimated total number of mature individuals of the species is:
(a) very low,
and:
(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
Reference
Thackway R, Cresswell ID (1995) (eds) 'An interim biogeographic regionalisation of Australia: a framework for establishing the national system of reserves.' Version 4.0. (Australian Nature Conservation Agency: Canberra).