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Prostanthera serpyllifolia is a small, spreading shrub reaching a height of 1 metre with a similar spread.
It is found on the western plains and far western plains of NSW, growing in similar habitat to P. aspalathoides; around Griffith and north of, then disjunctly south and south-east of Mildura, on the border with Victoria. It grows in the approximate north-west corner of Victoria, extending well into South Australia (to between Ceduna and Penong), then disjunctly on the south coast of Western Australia, to Albany and north-of.
It grows in mallee woodlands, on sandy and loamy soils, often with a limestone influence.
All plants in NSW are regarded as Prostanthera serpyllifolia subsp. microphylla.
Prostanthera have simple, opposite and usually odorous leaves. In this species, leaves are to 3 mm long x up to 2 mm wide; ovate, deep green, crowded and glossy. As with most mintbushes, the foliage is aromatic and rather attractive.
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, the flowers are rpdocued soliatrily in leaf axils, tubular, to 2 cm long and compressed sideways; reddish with yellow tips, bluish-green or yellow, with the flowering period extending from August to December. The species with tubular, compressed flowers, such as Prostanthera serpyllifolia, are in what is known as the Kalanderia section. Another species in this section is Prostanthera aspalathoides (see our article). Mintbushes with these tubular flowers would possibly be more attractive to honeyeaters and other birds, rather than insects.
Fruits are mericarps (can be called nutlets). Four are produced produced at the base of the calyx.
Not a great deal can be found online about its cultivation potential. It is not known how well it can be grown in east-coastal gardens. Check with local native nurseries for availability. There may be grafted forms available.
Prostanthera serpyllifolia is an ideal plant for rockeries and native cottage gardens, especially in drier areas. It likely needs a sandy soil to thrive. It is an interetsing inland plant.
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.
Propagation, from cuttings, is fast and satisfying. 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.
serpyllifolia – Latin – having leaves like Thymus serpyllum (Breckland Thyme).
This species is not considered to be at risk of extinction in the wild.
NSW Flora Online (PlantNET) – Prostanthera serpyllifolia profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~serpyllifolia
Western Australian Herbarium – Florabase – The Western Australia Flora – Prostanthera serpyllifolia profile page https://florabase.dpaw.wa.gov.au/browse/profile/6924
Wikipedia – Prostanthera serpyllifolia profile page https://en.wikipedia.org/wiki/Prostanthera_serpyllifolia