An erect, bushy, aromatic shrub growing to 2 metres tall and to 3 metres wide.
It is found growing in the Central Tablelands of NSW, from Mt Vincent to Genowlan Mountain in the Capertee Valley. 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).
Prostanthera have simple, opposite and usually odorous leaves (a typical Lamiaceae feature). In this species, leaves are in opposite pairs (rarely in 3-leaf whorls), to 13 mm long and 10 mm wide, 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 10 mm long and 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 are mericarps (can be called nutlets). Four are produced produced at the base of the calyx.
In a garden situation, is a hardy and quick growing plant in a well-drained, moist position with some shelter from direct summer sun. It is known to be cultivated, despite its threatened status. Plants may be difficult to source but there are some online avenues for purchase.
Should be pruned back annually by about one third if a bushy shape is to be retained.
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.
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.
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 cineole being a major component. Prostanthera sieberi, P. incisa and P. staurophylla are quite pleasantly overpowering in their exudates when crushed. Oil from the leaves of some species is distilled for use in cosmetics and as soap additives.
Prostanthera stricta is likely to be fire sensitive, with recruitment occurring from the soil seed bank.
Most Prostanthera species will regenerate from seed after fire with some species exhibiting an ability to reshoot from basal areas and stem buds. Populations are often clonal (referred to as ramets), with plants produced from lateral runners.
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 – Latin – strictus, meaning “pulled together” or “rigid”, presumably referring to the plant having an erect and upright habit of growth.
This species is listed as threatened with extinction under both State and Commonwealth legislation, with the category of Vulnerable.
NSW Office of Environment and Heritage – Threatened Species Profiles – Prostanthera stricta profile page https://www.environment.nsw.gov.au/threatenedspeciesapp/profile.aspx?id=10681
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.
Australian Native Plants Society Australia – Prostanthera information page
Wikipedia – Prostanthera stricta profile page