Prostanthera linearis

Narrow-leaved Mint Bush

Family: Lamiaceae

An erect shrub to a height of 3 metres with a narrow spread to about 1 metre. It is found in dry eucalyptus forest, often by streams in sandy or gravelly clay soils.

Its northern limit in NSW is around Gosford, extending down the coast to Milton and west to the Blue Mountains, but it also occurs in disjunct patches in Queensland.

Stems often square to round, leaves are in opposite pairs or whorls of 4, (rarely in 3-leaf whorls), narrow egg-shaped to linear, to 45 mm long and to 3 mm wide, on a petiole less than 2 mm long, dark-green and glabrous.

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 the flowers are arranged in leaf axils near the ends of branchlets with attached bracteoles to 3 mm long at the base. The petals are to 12 mm long and white, often with tinged with pinkish-mauve and fused into a tube for part of their length. Flowers are produced in leaf axils towards the top of the plants, occurring September to December.

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

In the garden


This species is available from some online nurseries but not overly common in cultivation. If plants can be sourced, it likely prefers a spot in dappled shade with a cool root run (they are often found along or near creeklines).

Can be pruned lightly to shape and can be grown into a tall shrub. Give an enriched but well-draining soil. Very attractive dainty plant when in flower.

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.

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.

Most Prostanthera species will regenerate from seed after fire with some species exhibiting an ability to reshoot from basal areas and stem buds. The exact response for this species is unknown.

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.
linearis – is from the Latin lineare, or ‘linear’, a reference to the long, narrow, linear shape of the leaves of this species.

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://en.wikipedia.org/wiki/Prostanthera_linearis

By Jeff Howes