Prostanthera densa

Villous Mint Bush

Family: Lamiaceae

Prostanthera densa is a small shrub. Its natural distribution is in five known areas in NSW, all very close to the coast – Nelson Bay, South Cronulla, Royal National Park (Marley), Helensburgh and Shoalhaven (northern peninsula of Jervis Bay).

It is found growing on a range of soil types – volcanic clay (Nelson Bay), sandstone outcrop (South Cronulla and Royal National Park), shale/sandstone transition (Helensburgh) and coastal sands (Shoalhaven).

It is an upright shrub, growing to potentially 3 m tall, although probably much shorter if grown in an open garden space. Leaves shortly ovate, about 1 cm long and wide (at base), narrowing at the tip, with a dense covering of hairs giving a raspy or velvet-like texture (depending on origin of propagation material).
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. Flowers are typically larger than the leaves and very attractive.
Fruits – 4 tiny nutlets produced at the base of the calyx.

In the garden

A gap filler or supplementary plant to create foliage contrast or texture variety, Lends itself to be useful in topiary gardens as a short-term plant.

Plants are known to live at least 5 years in the wild.

Prune after flowering to encourage a dense round shape.

Will tolerate a sunny position – probably best if not too hot. Give adequate drainage.

Allow good air flow. Likely to be frost intolerant. Will likely need a light sandy soil to do well.

Possibly affected by insects (galls) that invade the stem, based on observations in the wild.

Propagation

Soft-tip cuttings

Other information

NSW: Listed as Threatened – Vulnerable (Biodiversity Conservation Act 2016)
Commonwealth: Listed as Threatened – Vulnerable (Environment Protection and Biodiversity Conservation Act 1999)

Likely responds from seed after fire, possibly after 12 months.

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.
densa – Latin. meaning dense – referring to the dense foliage.

References:
• NSW Flora Online – PlantNET (http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~densa)
• Surveys conducted by Australian Plants Society and Dan Clarke for the NSW Saving our Species Program.

By Dan Clarke