Prostanthera askania

The Cut-leaf Mintbush (Prostanthera askania) is locally restricted to several catchment areas of the Gosford and Wyong Local government Area's (LGA). Issues relating to the occurrence and conservation of this species developed in conjunction with the preparation of detailed conservation and ecological assessments for the closely related Somersby Mintbush (P. junonis). While still under threat due to its restricted distributional range and secondary impacts of development, the habitats of the Cut-leaf Mintbush are not exposed to the same level of direct loss through land development as the habitats of the Somersby Mintbush.

Conservation Status

Listed as Endangered in NSW under Schedule 2 of the Threatened Species Conservation (TSC) Act, 1995. 
Also listed as Endangered under the Commonwealth Environmental Protection and Biodiversity Conservation Act, 1999.

Description

This species is an erect, open, spreading shrub 1 to 3m high. The branches and leaves are strongly aromatic and densely covered with long, spreading hairs. Leaves are ovate (12 – 25 mm) long, dull powdery green in colour, with deep incisions forming lobe-like teeth which are directed forwards. Flowers are pale mauve to mauve.¹

Other Characteristic Features

Flowering Time: Flowering usually occurs between September and November, however the timing of both flowering and fruiting can be variable.^1&2

Fire Response: This species is likely to be fire-sensitive given the moist forest habitats it occupies.²

Life Span: This species is a perennial species. Individuals have been known to survive for in excess of 7 years.

Reproduction: Reproduction is by seed. In some locations it appears to propagate vegetatively by ‘stem-layering’ where prostrate branches take root if they remain in contact with the soil.^1&2

Site Characteristics

Vegetation Type: Occurs in tall moist sclerophyll forest and warm temperate rainforest communities, and in the transition zone between them.¹

Topography: Occurs adjacent to, but not immediately in, drainage lines on flat to moderately steep lower slopes.¹

Soils: Favours Narrabeen Sandstone and alluvial soils within the Yarramalong, Wyong and Erina Soil Landscapes.²

Where this Species can be Found

Map of Distribution (PDF file, 1.4Mb)

Occurs over a range of less than 12 km in the upper reaches of creeks that flow into Tuggerah Lake or Brisbane Water within the Wyong and Gosford local government areas. 

Gosford:  Populations are known from Narara Creek and the Erina Creek–Fires Creek area.

Wyong:  Populations are known from Ourimbah Creek, Narara Creek, Dog Trap Gully, Chittaway Creek and Berkeley Creek.

Lake Macquarie: Not presently known to occur in Lake Macquarie.

Where is this Species Habitat Protected?

This species is not known to occur within any National Park, Nature Reserve or State Conservation Area.³ It is known to occur within Strickland State Forest.²

Threats to Survival

• The main threats to the survival of the species are habitat loss due to clearing and other modifications, including roadside maintenance activities and bushfire hazard reduction activities.
• Inappropriate fire regimes, too short a time between fires.
• Habitat degradation from bushrock removal, competition by weeds especially Lantana, dumping of rubbish and garden waste, and altered drainage flow patterns due to urban development.
• Trampling by recreational BMX or trail bikes and walkers.
• Other threats or potential threats include climate change and dieback caused by the root-rot fungus Phytophthora cinnamomi.

The species has been identified as being affected by the following Key Threatening Processes:

• Clearing of native vegetation.
• High Frequency Fire resulting in the disruption of life-cycle processes.
• Bushrock removal.
• Alteration to the natural flow regimes of rivers, streams, floodplains and wetlands.
• Anthropogenic climate change.
• Infection of native plants by Phytophthora cinnamomi, causing ‘dieback’.

Management Issues

• When undertaking hazard reduction burns, ensure staff are able to identify the species and are aware of its habitat.
• Prevent fires occurring more frequently than every 25 years in potential habitat, and prevent fire altogether in rainforests.
• Undertake targeted searches for the species in known or potential habitat prior to any clearing activities for developments, roads, power line or infrastructure maintenance or weed control activities.
• Undertake weed control as required using removal methods that will not directly injure the species.
• Protect and actively manage populations on private land through covenants, fencing and the preparation of site-specific vegetation management plans.
• Improve vegetative connectivity within and between areas of known and potential habitat through revegetation and regeneration programs.
• Monitor population health and numbers for any changes.

Useful Web links:

• Department of Environment and Climate Change www.environment.nsw.gov.au
• Plant Net – www.rbg.gov.au

Further Reading

• Conn, B. (1997). Four rare and/or threatened new species of Prostanthera Section Prostanthera (Labiatae) from New    South Wales. Telopea 7(3), 231-244.
• Fairley, A. (2004) Seldom seen: rare plants of greater Sydney. Reed New Holland, Sydney.
• C.L. Murphy Ed. (1993) Soil Landscapes of the Gosford/Lake Macquarie 1:100,000 sheet, Soil Conservation Service of NSW.

Bibliography:

1. Harden G.J. (ed.) (1992). Flora of New South Wales Vol. 3. UNSW Press, Kensington, NSW.
2. NPWS (2004). Draft Prostanthera askania Recovery Plan. NSW DEC, Sydney.
3. NSW Scientific Committee (1998) Final determination to list Prostanthera askania (a shrub) as an Endangered species. DEC (NSW), Sydney.