Prostanthera stricta

Mount Vincent Mint Bush

Family: Lamiaceae

An erect, bushy, aromatic shrub growing to 2 metres tall and to 3 metres wide.

It is found growing from Mt Vincent to Genowlan Mountain in the Capertee Valley, in the Central Tablelands of N.S.W. A variant of this species has been historically recognised – known as P. aff stricta, which occurs further north in the Upper Hunter Valley at Dingo Creek and the Widden and Baerami Valleys.

It is a listed threatened species in the wild.

It is often a locally dominant undershrub in heath or scrub communities along cliff edges, or as an understorey species within a range of open forest or tall open forest types (especially along creeklines) or in adjacent transitional communities.

Branches are hairy and aromatic; elongated and cylindrical (not square).

Leaves are in opposite pairs (rarely in 3-leaf whorls), ovate to elliptic with the upper surface covered by hairs, dark-coloured on the upper surface, whitish underneath, the midrib and lateral veins prominent underneath and impressed above, giving the surface a puckered appearance. The leaf stalk is only 0.5 mm.

Plants referred to as Prostanthera aff. stricta, differ from the type form by having leaves which are broad ovate to ovate, and leaf bases which are often broadly rounded. Its leaves may appear triangular when the leaf margins are strongly curved downwards, as in periods of drought. The whole plant also appears more hairy.

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 pale mauve to deep purple, rarely white, to 9 mm long by about 10 mm wide, occurring in compact arrangements on the upper end of branches which gives the plant a distinctive appearance. Flowering occurs from winter to spring.

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

In the garden

In a garden situation, is a hardy and quick growing plant in a well-drained, moist position with some shelter from direct summer sun. Should be pruned back annually by about one third if a bushy shape is to be retained.
Plants may be difficult to source, given its threatened status, but there are some online avenues for purchase. It prefers a sandy, well-drained soil.

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

There is a tip from the publication: “Letters to Garden Lovers”, Australian Home Beautiful, April 1938, to regularly and lightly prune branches all through the year rather than give plants a heavy prune once a year.
Be careful not to eliminate flower buds, however.

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.

This species is listed as threatened with extinction under both State and Commonwealth legislation with the category of Vulnerable

Prostanthera stricta is likely to be fire sensitive, with recruitment occurring from the soil seed bank.

Populations are often clonal (referred to as ramets), with plants produced from lateral runners.

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

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.

stricta – from Latin strictus, meaning “pulled together” or “rigid”, presumably referring to the plant having a having an erect and upright habit of growth.

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=10681
https://en.wikipedia.org/wiki/Prostanthera_stricta

By Jeff Howes