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A shrub reaching about 3 metres high by 2 metres (or more) wide, very aromatic.
It has a large natural range, growing on in the coastal, tablelands, western slopes and western plains of NSW (with some morphological variation); from as far north as west of Dorrigo, and Upper Horton with records as far west as Coonabarabran and near Walgett (in the north); as far west as Hay in the south; and growing through the Lithgow-area and southern tablelands as well as the alpine region. It grows through most of Victoria as well as in Tasmania around Launceston and St Marys-Scamander area.
It is often found in wet sclerophyll forest as well as rainforest margins, as well as dry sclerophyll woodland and rocky areas, usually on sandy soils or enriched sandy loams.
Prostanthera have simple, opposite and usually odorous leaves. In this species, the leaves are broad ovate to obovate or circular, to 20 mm long by 15 mm wide, with a rounded apex; often with lobed margins; mid green to dark green and aromatic.
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 to 15 mm long, and are produced in leaf axils in clusters or spikes, purple-mauve to purple and sometimes pink-ish.
Fruits are mericarps (can be called nutlets). Four are produced produced at the base of the calyx.
Author’s notes:
This species is another of the more commonly cultivated. It is easy to grow in most cases.
The Round-leaf Mint Bush reaches a height of two metres in our cold climate garden. The foliage is very aromatic. Flowering is in spring when the plants become covered with blooms. The flowers are conspicuous and profuse. Usually they are purple but there is also a pink-flowered form.
In dry periods plants may sometimes wilt. Judicious watering or a rainfall of about ten millimetres or more will bring plants bouncing back.
Prune after flowering to maintain a bushy shape. Both foliage and flowers are attractive features.
P. rotundifolia could be cultivated in shrubberies or planted beside a path where as you brush against the plant the perfume is released from the foliage. The species could also be planted under mature eucalypts to create a woodland effect. In these situations, this Mint Bush will light up your woodland in spring.
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.
The Round-leaf Mint Bush propagates enthusiastically 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.
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.
rotundifolia – Latin – from rotundus – meaning “round” – referring to the rounded foliage of this species.
This species is not considered to be at risk of extinction in the wild.
NSW Flora Online (PlantNET) – Prostanthera rotundifolia profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~rotundifolia
Australian Native Plants Society Australia – Prostanthera rotundifolia profile page https://anpsa.org.au/plant_profiles/prostanthera-rotundifolia/
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.