Prostanthera marifolia

Seaforth Mintbush

Family: Lamiaceae

A wiry, low spreading to erect, straggly and open-branched shrub, up to 0.5 m high.

It is currently only known from the northern Sydney suburb of Seaforth and has a very highly restricted distribution within the Sydney Basin Bioregion.

The single population is within an urban area, restricted to three small sites over about 5 square kilometres. It is listed as threatened with extinction.

Grows in dry sclerophyll woodland on enriched sandstone-shale to lateritic soils.

Branches / stems are sparsely hairy and square.

Leaves are in opposite pairs (rarely in 3-leaf whorls) and stems often square (maybe not always), green, slightly hairy, with an ovate to elliptic or triangular shape, to 12 mm long and to 6 mm wide, and may have one lobe on each side, rarely two. The mid-rib/vein is prominent on the underside of the leaf.

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 purple to mauve, 7 to 10 mm long and appear close to the stem, just above the leaf, in leaf axils. Petals are fused into a tube for most of their base, fanning out to lobed petals, with short anthers and a scattering of hairs. Main flowering time is spring.

Fruits – 4 tiny nutlets (mericarps) produced at the base of the calyx and are slightly oval and cylindrical, approximately 1 mm long and 0.5 to 0.7 mm in diameter.

In the garden

A plant not readily available in cultivation due to its threatened status. It may become more readily available in the future from bushcare nurseries.

Would grow well on a sandy-loam to clay-loam soil in dappled shade. Provide good drainage. Plants tends to be ground-hugging, so allow some room to spread.

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

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

Synonyms: Has been known as Prostanthera sp. ‘Manly Dam’

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.

This species is listed as threatened with extinction under both State and Commonwealth legislation with the category of critically endangered.

This species was previously recorded from the Sydney harbour region and was presumed extinct. All attempts to recollect this species were unsuccessful until 2001.

Previously the taxonomic status of this name was uncertain and the species was presumed to be extinct. Users were encouraged to apply this name to current living plants only after careful consideration. However, the re-discovery of a few plants of this species in the Sydney region has allowed a detailed circumscription to be provided here.

This species is also very similar to Prostanthera densa and a case for lumping them has been raised. However, latest DNA data shows they should be retained as separate species. Further confusion has arisen from the fact that botanist A.A. Hamilton considered plants occurring at Helensburgh in NSW, to be P. marifolia, rather than P. densa.

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 highly likely from seed.

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.

marifolia – Latin for “sea-leaves”, which is probably a reference to where the plant grows naturally.

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://www.environment.nsw.gov.au/threatenedSpeciesApp/profile.aspx?id=20101
https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~marifolia

By Jeff Howes