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A soft-wooded shrub to 50 cm high with cylindrical and ridged stems bearing hairs and with some warty-glands.
It has a restricted natural occurrence in NSW, occurring over Greater Sydney, from Mangrove Mountain, south through Sydney and the eastern Blue Mountains – not usually found south of the CBD. Most occurrences are in north and north-west Sydney.
It is a listed threatened species in the wild.
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 alternate to opposite, or rarely in whorls of 3 or 4; to 20 mm long and to 2 mm wide, with glandular hairs on the margins, giving a toothed appearance.
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 to rarely paired, to 25 mm across, deep lilac-pink to reddish-pink (occasionally pale-pink) with flower stalks and sepals covered with dark-red glandular hairs; flowering mostly July to November.
Tetratheca spp. produce fruit as capsules which open longitudinally. In this species, the capsules are to 7 mm long, with seeds to 4 mm long, brown in colour.
This species is not known to be cultivated as it is a listed threatened species in the wild. It is likely unavailable for cultivation. It may be more readily cultivated in the future. Check with native nurseries for availability.
Some Tetratheca spp. are cultivated commonly, especially T. thymifolia and they make very attractive additions to gardens.
Plant them along open borders or in rockeries for best affect, with well-drained soils and some shade during the warmer months.
Propagation can be carried out from seed but this is rarely available.
Cuttings of hardened, current season’s growth usually strike fairly-readily. Cuttings of young suckering shoots will also work well provided the propagation mix is well-drained. The use of a root-promoting hormone is advised for greater success. Cuttings are best done from November to April.
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.
glandulosa – Latin referring to “glandular” – referring to the conspicuous glands on various plant parts such as leaves.
This species is listed as being at risk of extinction in the wild at the State level with the category of Vulnerable.
NSW Flora online (PlantNET) Tetratheca glandulosa profile page: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Tetratheca~glandulosa
NSW Government Office of Environment and Heritage – Tetratheca glandulosa profile page https://www.environment.nsw.gov.au/threatenedspeciesapp/profile.aspx?id=10798
Wikipedia profile page for genus Tetratheca (including a list or many of the species): https://en.wikipedia.org/wiki/Tetratheca
The Family Tremandraceae – APS NSW https://austplants.com.au/resources/Documents/South-East-Documents/Articles_About_Plants_and_Gardens/The_Family_Tremandraceae_John_Knight.pdf