Prostanthera junonis

The Somersby Mintbush (Prostanthera junonis) has become a significant species in relation to planning and management of threatened plant populations due to its occurrence in a localized area identified for large scale industrial development. The occurrence of this species was identified after large areas of the Somersby Industrial Estate had been developed. In 1993 Prostanthera junonis was re-discovered at the Somersby Industrial Estate after not being recorded in NSW for 67 years.¹ With the introduction of legislation identifying assessment requirements for threatened flora and fauna species the importance of the Somersby area for this locally restricted endangered species was recognised. Detailed surveys, consultations and management plans undertaken over a 10 year period has resulted in some pioneering concepts in relation to land development, ecological assessment and conservation planning for this important endangered species.

Conservation status 

Listed as endangered in NSW under Schedule 1 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 a low spreading shrub 0.1 - 0.3 m in height and up to 1 m in diameter (occasionally up to 1m high). Leaves are oval in shape, dull green on top and paler below. Flowers are 8 - 12 mm long and pale mauve to almost white with brown spots in the centre.

Other Characteristic Features

Growth Characteristics: In open sites, branches are wiry and often prostrate to 0.1 to 0.3m high. Where vegetation is denser, the plants have long spindly branches which weave through other vegetation for support and can grow up to 1m high.

Flowering Time: The flowering period is October to mid-December depending on weather/site conditions.

Reproduction: Fertilization by Native bees. Reproduction is by seed.

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

Fire Response: Mature plants appear to be incapable of re-sprouting after fire however, fire may trigger seed germination.

Similar Species

This species is commonly mistaken for Hemigenia purpurea. The noticeable differences between these species are:

• Hemigenia purpurea has a calyx (flower cup) with five long teeth as opposed to two lips in P. junonis;
• Hemigenia purpurea has linear leaves, in whorls of three occurring densely along the branches, while P. junonis has elliptic to narrowly elliptic leaves that are opposite and widely spaced along the branches.

Site Characteristics

Vegetation Type: Usually in open forest, low woodland or open scrub. It occurs in both disturbed and undisturbed sites.

Topography:  Gently undulating country on the Somersby Plateau.

Hydrology: Typically found in well drained sunny areas.

Soils:  It occurs on sandy soils from both the Somersby and Sydney Town soil landscapes derived from weathered Hawkesbury Sandstone.

Where this Species can be Found

Map of distribution (PDF file, 691kb)

Has a north-south range of approximately 19 km on the Somersby Plateau in the Gosford and Wyong local government areas.

Gosford: Somersby Industrial Area, Reeves Road Reserve, Brisbane Water National Park, Wisemans Ferry Road, Somersby.

Wyong: Ourimbah State Forest.

Lake Macquarie: Not presently known in Lake Macquarie.

Where is this Species Habitat Protected?

Gosford: Brisbane Water National Park and Ourimbah State Forest.

Threats to Survival

• Habitat degradation resulting from weed invasion, stormwater runoff, unrestricted access and inappropriate fire regimes.
• Habitat loss due to clearing for agriculture, industrial development and bushfire hazard reduction works.
• Susceptibility to plant pathogens such as fungal root rot (Phytophthora cinnamomi) and root nematodes.
• Bushfire and inappropriate fire regimes.
• Habitat removal through industrial development, sand mining and road works.

This Species is listed as being affected by the following Key Threatening Processes:

• Clearing of native vegetation.
• Infection of native plants by Phytophthora cinnamomi (Fungus root rot).
• High frequency fire resulting in disruption of life cycle

Management Issues

• Ensure staff undertaking hazard reduction burns are able to identify the species and are aware of its habitat.
• Apply fire regimes which maintain floristic and structural diversity.
• Undertake targeted searches for the species in known or potential habitat during its flowering period prior to any development or clearing activities.
• Install stormwater control mechanisms to prevent runoff from development upslope of populations.
• Limit access to populations through fencing and signage.
• Undertake weed control as required using removal methods that will not impact on the species, by hand pull or cut and paint method.
• 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/regeneration programs.
• Monitor population health and abundance to detect change.

Useful Web links:

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

Further reading:

• Harden G.J. (ed.) (1992). Flora of New South Wales Vol. 3. UNSW Press, Kensington, NSW. 
• Murphy C.L. Ed. (1993) Soil Landscapes of the Gosford/Lake Macquarie 1:100,000 sheet, Soil Conservation Service of NSW.
  
• NPWS (2000) Somersby Mintbush Prostanthera junonis Recovery Plan. NPWS, Sydney.

Bibliography:

1.  Tierney, D.A. = Gross C.L. (2001) Prostanthera junonis; Is Recovery Possible Pac. Con. Biol. Vol 7 118-123, Surrey Beatty & Sons Sydney.