Prostanthera cineolifera

Singleton Mint Bush

Family: Lamiaceae

An erect shrub to 4 metres tall to 2 metres wide, which is strongly aromatic.

Stems are hairy and glandular and often square.

It is confined to the Hunter Valley in NSW, near Scone, Cessnock and further south at St Albans, and is typically found on very shallow sandy soils on sandstone ridges and slopes, in dry sclerophyll woodlands. It is a listed threatened species.

Leaves are in opposite pairs or rarely in 3-leaf whorls, narrow egg-shaped, to shortly lanceolate, light green, to 50 mm long and to 12 mm wide, on a petiole to 7 mm long.

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 arranged in terminal clusters with flowers having attached bracteoles, to 2 mm long that fall off as the flowers develop.
The petals are fused into a tube, light pale-mauve to dark purple-mauve, to 12 mm long by about 10 mm wide. Flowers are typically darker on the inside.
Flowering occurs from September to October.

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

In the garden

Not readily known in cultivation as it is a listed threatened species. May be able to be sourced from nurseries in time.

Likely needs a sandy well-draining soil to thrive. Grow in part-shade and prune lightly after flowering for best results.

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 sieberiP. incisa and P. staurophylla are quite pleasantly overpowering due to their exudates when crushed.

Prostanthera sieberi, P. incisa and P. staurophylla are quite pleasantly overpowering due to 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.

A listed threatened species in NSW and at Commonwealth level with the status of vulnerable.

Most Prostanthera species will regenerate from seed after fire with some species potentially having an ability to reshoot from basal areas and stem buds.

The fire response is unknown for this particular species.

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.

cineolifera – Latin – named for the leaves bearing large amounts of cineol in the essential oils of the leaves.

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=10672

By Jeff Howes