Prostanthera stenophylla

Mint bush

Family: Lamiaceae

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 forest growing in in sandy loamy soils and sandstone outcrops that are colloquially known as ‘pagodas’.

Branches / stems are densely hairy with spreading hairs and square-shaped.

Leaves are opposite pairs (rarely in 3-leaf whorls) and covered with a dense mat of hairs and give off a strong aroma when crushed, narrow egg-shaped to narrow elliptic but appear oblong due to the edge being curved downwards or rolled under, to 15 mm long and to 2 mm wide, dull green above, paler below on a very short petiole.

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

In the garden

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.

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.

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.

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.

stenophylla – Latin – refers to the narrow leaves of this shrub species

Not considered at risk in the wild, although it has a very limited range.

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_stenophylla
https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~stenophylla

By Jeff Howes