Prostanthera junonis

Somersby Mint Bush

Family: Lamiaceae

A low spreading or straggling shrub to 1 metre high and up to 1 metre in diameter.

It grows naturally in sclerophyll forest and woodland in sandy-loam soils on sandstone.

It is restricted to the Somersby Plateau in the Gosford area of NSW and has a north-south range of approximately 19 km on the plateau, in the Gosford and Wyong local government areas. It grows at places such as the Australian Reptile Park at Somersby. Also reported from Mangrove Mountain.

It is a listed threatened species in NSW.

Its habit can be variable; in open sites, branches appear wiry and are often prostrate. However, where vegetation is denser, the plants have long spindly branches which weave through other vegetation and can grow up to 1 m long. Branches moderately covered with long hairs. Plants are generally non-aromatic.

Prostanthera have simple, opposite and usually odorous leaves. In this species, leaves are oval in shape, dull green above and paler below, to 14 mm long and to 5 mm wide.

Flowers have a shape described as labiate (applies to all Lamiaceae flowers) with 5 petals varying in their size, fused at their base, produced in leaf axils. One of the identification features for Prostanthera is that the 5 calyx parts (basal whorl of the flower) are fused into 2 lips.

In this species flowers are to 12 mm long by 10 mm wide, pale-mauve to almost white with brown spots in the throat. The petals are fused into a tube for about 3 mm. Flowers are produced singularly, at the base of paired leaves and are produced from October to February.

Fruits – 4 tiny nutlets (mericarps) produced at the base of the calyx.

In the garden

Not readily available for cultivation, likely due to its threatened status. It may become available in the future. It likely needs a sandy soil to thrive with good drainage. This plant grows more readily when not competing with the cover of other plants.

A Prostanthera in full bloom is a magnificent sight and there are so many colours to choose from for your garden. These plants are found in all states in varied soil conditions and climate and thus while it may be a challenge to grow some species many are easy in a garden situation.

A few basic growing tips are:

• Good drainage is essential. Raised beds ensure this
• Water new plants until established, weekly or as required.
• Do not over water, as this can induce root rot and fungal infestation.
• They prefer moist root runs.
• Plant drooping is an indicator of dryness

Positioning of prostantheras as border plants or near pathways is recommended as the mint odour is released when brushed against.


Plants may be grown from fresh seed. However, cuttings are frequently and reliably used, usually semi-hard wood or soft tip material, which strike well in spring or autumn.

Other information

Synonym: Prostanthera sp. ‘Somersby’ (before it was formally published). Very difficult to identify when not flowering.

Prostanthera is a diverse group of about 100 species, endemic to Australia, occurring in all states. There are still many unresolved taxa and species complexes, with new forms regularly being found. Natural hybrids occur between several species and most species appear to be capable of hybridizing when in cultivation. NSW currently has about 52 species, some of which are species-complex and others which are threatened with extinction.

Some 80% of mints contain aromatic oils within their leaves with oil of cineol being a major component. Prostanthera sieberi, P. incisa and P. staurophylla are quite pleasantly overpowering due to their exudates when crushed. Oil from the leaves of some species is distilled for use in cosmetics and as soap additives.

Most Prostanthera species will regenerate from seed after fire with some species exhibiting an ability to reshoot from basal areas and stem buds. Mature plants appear to be incapable of resprouting after fire. This editor has heard observational evidence that plants regenerate from seed in the 12 to 24-month period after fire (similarly to Prostanthera densa).

Prostanthera – from the Greek prosthike (προσθήκη) which translates to ‘addendum’, and anthir (ανθήρ) meaning anther – referring to the anthers which have an appendage of tissue.

junonis – honours Mrs June Gay (d. 1997), a volunteer at the National Herbarium of NSW, who assisted botanist Barry Conn with research and curatorial help on Prostanthera.

This plant is listed as threatened under both State and Commonwealth legislation with the category of endangered at both levels.

NSW Flora Online (PlantNET) – Prostanthera junonis profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~junonis

Australian Native Plants Society Australia – Prostanthera – The Mint Bushes Information Page

NSW Office of Environment and Heritage – Threatened Species Profiles –                              Prostanthera junonis profile page  https://www.environment.nsw.gov.au/threatenedspeciesapp/profile.aspx?id=10678

By Jeff Howes. Editing and additional text by Dan Clarke.