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A shrub to small tree, potentially reaching 8 metres tall, by several metres wide.
It is a rare mint bush, growing on the Northern Tablelands of NSW, mostly close to the NSW-Queensland border; in an area east of Tenterfield, north-west to Jennings (Boonoo Boonoo National Park), and towards Stanthorpe in Queensland.
It grows on sheltered creeklines amongst granite boulders, in sclerophyll forest.
Prostanthera have simple, opposite and usually odorous leaves. In this species, the leaves are ovate up to 8 cm long by 2 cm wide, strongly aromatic with prominent stalks; dull olive-green above and paler beneath.
Flowers have a shape described as labiate (applied to all Lamiaceae flowers) with petals varying in their size, purple to lilac, produced in leaf axils. One of the identification features for Prostanthera is that the 5 calyx parts (sepals; basal whorl of the flower) are fused into 2 lips. In this species, flowers are 2 cm long, white in colour and carried in terminal sprays (botryoids), conspicuous and profuse in spring. They are similar in colour and size to the flowers of the better known Prostanthera lasianthos.
Fruits are mericarps (can be called nutlets). Four are produced produced at the base of the calyx.
Author’s notes:
A nice plant to grow. Plants have reached 2 metres tall after 3 years in our cold climate garden.
Both foliage and flowers are attractive features. Light pruning is beneficial and will help to shape the plant and promote better flowering.
Prostanthera petraea deserves to be widely cultivated. Not only because it is a handsome, free-flowering shrub but because of its rarity. Extensive cultivation reduces the risk of extinction.
This native mint bush would be an interesting and aromatic addition to a native shrubbery.
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
Positioning of prostantheras as border plants or near pathways is recommended as the mint odour is released when brushed against.
Prostanthera petraea propagates readily from cuttings.
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.
The species was named in 2006. Some botanical publications, prior to 2006, list this mint bush as Prostanthera species B.
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.
Likely regenerates from seed after fire, possibly after 12 months.
Prostanthera – from the Greek prosthike (προσθήκη) which translates to “addendum” (root of prosthetic), and anthir (ανθήρ) meaning anther – referring to the anthers which have an appendage of tissue.
petraea – from the Ancient Greek petra (πέτρα) referring to “rock” or “of rock” – referring to this species habitat where it grows amongst large boulders. The species name is also intended to capture the meaning of Boonoo Boonoo which means “large rocks” in First Nations language.
This species is not considered to be at risk of extinction in the wild but is considered rare.
NSW Flora Online (PlantNET) – Prostanthera petraea profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~petraea
Wikipedia – Prostanthera petraea profile page https://en.wikipedia.org/wiki/Prostanthera_petraea