An erect, slender shrub to 2 metres tall to less than 1 metre wide.
It is only known from the Wollemi National Park on the Central Tablelands of NSW, where it is found in sclerophyll woodland growing in sandy loamy soils and sandstone outcrops that are colloquially known as ‘pagodas’.
Branches / stems are densely hairy with spreading hairs and square-shaped.
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) and covered with a dense mat of hairs and give off a strong aroma when crushed; to 15 mm long and to 2 mm wide, dull green above, paler below on a very short petiole; narrow egg-shaped to narrow elliptic but appear oblong due to the edge being curved downwards or rolled under.
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 groups of four to six on short side shoots in leaf axils. The petals are pale bluish-mauve to violet to pink, to 12 mm long with part of its length fused into a tube, occurring in most months with a peak flowering in spring.
Fruits are mericarps (can be called nutlets). Four are produced produced at the base of the calyx.
This species has been in limited cultivation for some years. The unofficial name of Prostanthera rylstonii has been used by plant nurseries since at least 2005.
One of the earliest mint bushes to flower and is frost and very drought hardy. Best grown in a well-drained soil in full sun for best results.
There is a naturally occurring pink form that can be purchased. This species is also sold as a hybrid, crossed with other species.
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 cineol being a major component. Prostanthera sieberi, P. incisa and P. staurophylla are quite pleasantly overpowering due to their exudates when crushed.
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.
stenophylla – Greek via Latin – stenos (στενός) meaning “narrow” and -phylla (φύλλα) meaning “leaves”, referring to the narrow leaves of this species
This species is not considered to be at risk in the wild, although it has a very limited range.
NSW Flora Online (PlantNET) – Prostanthera stenophylla profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~stenophylla
Australian Native Plants Society Australia – Prostanthera information page
Wikipedia – Prostanthera stenophylla profile page