Prostanthera prunelloides

Mint Bush

Family: Lamiaceae

An erect to spreading shrub to 2 metres tall.

It is found in dry sclerophyll forests and woodland, often near creeks, on sandy soils over sandstone, on the coast, tablelands and central western slopes of New South Wales, from Murwillumbah in northern NSW, to the Budawang Range, with most of its occurrence from the Hunter Valley to Batemans Bay.

Branches are four-ridged (square) and slightly aromatic.

Leaves are in opposite pairs (rarely in 3-leaf whorls, egg-shaped to circular, to 65 mm long and to 40 mm wide, on a petiole to 15 mm long, slightly aromatic.

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 arranged in compressed groups / clusters on the ends of branchlets, each flower with bracteoles about 2.5 mm long at the base, but that fall off as the flower develops.
The petals are white to pale mauve and 12 to 15 mm long with petals fused into a tube for part of their length.

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

In the garden

Not commonly cultivated and plants may be hard to source. It is likely just one of many species that needs to be trialled in cultivation.
Would likely prefer a well-drained sandy soil in full-sun to part shade.
Could likely be pruned to a nice shape. Best approach is a light tip prune after flowering.

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 of Prostanthera, 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.

prunelloides – resembling species of Prunella, another genus of the Lamiaceae, eg: the NSW weed Prunella vulgaris. The resemblance is likely in the leaves and/or clustered flower-heads.

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_prunelloides
http://anpsa.org.au/prostantheraSG/prostanthera12.pdf

By Jeff Howes