A shrub to about 1 m high, often with many stems radiating out to form a width about 0.5 m wide.
It has a widespread natural distribution, along the entire coast of NSW and generally just into the tablelands; along the coast from border to border and as far west as Batlow-Tumbarumba (where it is largely disjunct here from plants closer to the coast), Goulburn-Wombeyan Caves, Jenolan Caves, Upper Blue Mountains, Oxley Wild River National Park and Tenterfield.
In Tetratheca spp., leaves are simple and can be arranged alternately or in opposite pairs or whorls. Some species can exhibit varying leaf arrangements (dimorphic). In this species, leaves are usually in whorls of 3 to 5 or sometimes 6, rarely opposite each other; to 20 mm long and 8 mm wide, more or less hairless to hairy and the margins loosely rolled down.
Tetratheca spp. tend to produce solitary or paired flowers in leaf axils, well beyond the foliage. They typically have 4 petals which resemble an even cross (some flowers can have 5 petals), with 8 stamens and 1 carpel. Flowers often point downwards (pendent) which attracts certain insects. In this species, flowers are single or rarely paired, deep lilac-pink or sometimes white; to 20 mm long; flowering most of the year.
Tetratheca spp. produce fruit as capsules which open longitudinally. In this species, fruit to 6 mm long, with a beak, with seeds to 3 mm.
This is one of the most widely-grown species in cultivation and is available from most native and even larger commercial nurseries.
To grow at its best, it needs to be planted in well-drained acidic soils in a sunny or semi-shaded aspect. Also tolerates light frosts.
It makes an ideal container plant.
There are several forms that have been selected for horticulture and all worth growing. There is also a white-flowered cultivar commonly sold.
It is a spectacular plant when in full flower and mature.
Propagation can be carried out from seed but this is rarely available. Cuttings of hardened, current season’s growth usually strike fairly readily. The use of a root-promoting hormone seems advantageous.
Tetratheca comprises around 50 to 60 species, endemic to Australia. They occur in all states with the exception of the Northern Territory. NSW currently has 16 species.
The flower colours have given rise to the common name for many species of “Black-eyed Susan”. However, note that this common name also applies to several exotic species.
Most Tetratheca spp. would die in a fire and regenerate from the seed bank.
Tetratheca – Ancient Greek – tetra meaning “four”, and theke meaning “sac or box”, relating to the condition of the stamens in the flowers which have four lobes or cells.
thymifolia – Latin referring to Thymus (the Thyme genus) and –folia – meaning “leaves” – capturing this species similarity to Thyme.
This species is not considered to be at risk of extinction in the wild.
NSW Flora online (PlantNET) Tetratheca thymifolia profile page: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Tetratheca~thymifolia
Plants of South Eastern Australia (LUCID Online Plant Identification Webpage / App) – Tetratheca thymifolia profile page https://apps.lucidcentral.org/plants_se_nsw/text/entities/tetratheca_thymifolia.htm
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.
Gardening with Angus – Tetratheca thymifolia profile page https://gardeningwithangus.com.au/tetratheca-thymifolia-black-eyed-susan/