A tall, graceful forest shrub (to small tree), highly variable in its habit and appearance. It ranges from a 10-metre high tree growing in sheltered forest, to a 2-metre high shrub growing in exposed montane areas. It is the largest member of the genus Prostanthera. It has historically been a taxonomically complex species.
It can be found growing by creeks and in the moist shade of dense, wet sclerophyll forests in Queensland, NSW, Victoria and Tasmania. In NSW, it grows all along the coastal and tablelands divisions and moved into the north-western slopes, from low to high altitude, in dry sclerophyll woodland and forest and well as wet sclerophyll forest to rainforest edged. They can be found as large plants on the headwaters of the Hawkesbury/Nepean River around Kangaloon, NSW, where at first glance, they resemble small willow trees.
Bark is green to dark brown to blackish, shallowly fissured longitudinally. Stems square. In large plants, the stem can be up to 15 cm diameter at the base.
Prostanthera have simple, opposite and usually odorous leaves (a typical Lamiaceae feature). They are dark green to green-grey, lanceolate to ovate, to 15 cm long and to 4 cm wide, and tapering to an acute apex. The leaf undersurface is paler. Leaves vary a lot in their shape, size and toothing.
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 white to pale mauve or bluish with purple to mauve spots in the throat, 10–15 mm long and wide, with a bell-shaped tube. Flowers are produced in large open terminal panicles to 12 cm long and 10 cm wide, occurring from November to March.
Fruits – 4 tiny nutlets (mericarps) produced at the base of the calyx.
This has been a popular plant in cultivation. It may depend on which form is sourced or purchased but the larger forms are spectacular in flower and well worth growing.
In a garden situation, with a good mulch and some watering, it is fast growing and will grow in light or stiff soils in sun or shade, but constant wind should be avoided.
It is also tolerant of light frost and snow. It is excellent for hiding a fence or as a tall hedge.
Plants will tolerate some enrichment from organic matter. Can be used to great effect with other shrubs and can likely tolerate heavier pruning than most of its relatives.
Usually, flowers are white but they are produced in large number in panicles, creating an attractive show. Flowers are food for native bees and wasps.
This species will also likely live a fair amount of years, if happy.
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.
Plants may be grown from fresh seed. However, this may give erratic results. Hence cuttings are frequently and reliably used, usually from semi-hard wood or soft tip material, which strike well in spring or autumn. In this species take cuttings of short laterals with heels in February to July; they may be slow to strike. Mist may rot cuttings.
This species is known by the following synonyms:
A number of variants have been identified over the years with uncertain taxonomic status.
In 2021, a comprehensive study was published (see references) which has split this species into 5 new species with Prostanthera lasianthos comprising a species with less variability (narrower taxonomic concept):
Other forms may still persist – a mauve-pink form, known as ‘Kallista Pink’ occurs in Kallista, not far from Melbourne, Victoria in the Yarra Ranges Shire. Other cultivars include ‘Mint Ice’, a form with variegated foliage from the Dandenong Ranges. Another tall cultivar, ‘Liffey Falls’, from Tasmania, has a lilac flower.
Sapling wood is hard and tough but flexible and has been used for fishing rods.
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. Some plants have been observed to reshoot from snapped basal stems.
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 but it likely has both abilities.
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.
lasianthos – from the Greek lasios (λάσιος) meaning ‘shaggy’ or ‘woolly’, and
–anthos (άνθος) ‘flower’, referring to the woolly flowers.
This species is not considered to be at risk of extinction in the wild.
NSW Flora Online (PlantNET) – Prostanthera lasianthos profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~lasianthos
Australian National Herbarium – Prostanthera lasianthos profile page https://www.anbg.gov.au/gnp/gnp3/prostanthera-lasianthos.html
Australian Native Plants Society Australia – Prostanthera Information Page
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.
Barry J. Conn, Murray J. Henwood, Kirstin M. Proft, Judith A. Scott, Trevor C. Wilson, and Rod S. Howes “An integrative taxonomic approach resolves the Prostanthera lasianthos (Lamiaceae) species complex,” Australian Systematic Botany 34(5), 438-476, (8 July 2021).