Prostanthera askania

Tranquility Mintbush

Family: Lamiaceae

An erect to spreading and sometimes scrambling, openly-branched shrub that grows to 3 metres high. Occurs in moist sclerophyll forest and warm temperate rainforest communities, and the ecotone between them. It has a very restricted geographic range, in the central coast subdivision of NSW, found on the upper reaches of creeks that flow into Tuggerah Lake and Brisbane Waters, within the Wyong and Gosford local government areas. It is listed as threatened with extinction in the wild.

Leaves are in opposite pairs with stems square and covered in long spreading hairs.

The leaves are strongly aromatic, to 40 mm long and to 25 mm wide, dull green and are somewhat egg-shaped, with very obvious teeth along the entire margin. Leaves are paler on the underside, covered with long spreading hairs and rounded at the apex.

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 (sepals; basal whorl of the flower) are fused into 2 lips.

In this species, 4 to 10 light mauve or bluish flowers appear in leafy clusters at the end of branches with petals to 15 mm long.

Flowering occurs from June to December and makes a pleasant show.

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

In the garden

An endangered plant in the wild so not commonly grown. However, it can be seen in cultivation in some places such as the Hunter Region Botanic Garden for conservation purposes.

Plants can likely be grown successfully, like many other mint bushes, if they can be sourced.

Not overly large in size and can be easily pruned to keep it smaller and to create density. Tip pruning after flowering is recommended. Plant in part shade and avoid areas that receive hot western sun.

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

Propagation

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

There are approximately 100 species, endemic to Australia. They occur in all States.

This genus is currently under revision, and several species complexes are unresolved. Natural hybrids occur between several species and most species appear to be capable of hybridizing when in cultivation.

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 in their exudates when crushed. Positioning of prostantheras as border plants or near pathways is recommended as the mint odour is released when brushed against. Oil from the leaves of some species is distilled for use in cosmetics and as soap additives.

Is listed as threatened with extinction with the category of endangered under both Commonwealth and State legislation.

A new and very small population was found in Bouddi National Park, at Macmasters Beach, in the last 20 years.

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.
askania – is named after Askania Park, a private reserve west of Ourimbah, where it grows in sheltered gullies. “Askania” is a name of several localities and a nature reserve in Russia and the Ukraine and has Greek roots (Askanios)

https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Prostanthera
http://anpsa.org.au/APOL2007/apr07-1.html
https://www.environment.nsw.gov.au/threatenedspeciesapp/profile.aspx?id=10671
https://en.wikipedia.org/wiki/Prostanthera_askania

By Jeff Howes, edited Dan Clarke