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Tetratheca juncea

Black-eyed Susan

Family: Elaeocarpaceae

A prostrate-sprawling and flexible, soft-wooded shrub, with winged-stems to 1 metre long, covered in minute warts. It grows in clumps, spreading using buried stems.

It has a restricted distribution in the wild, growing south from Buladelah in NSW, through the Newcastle and Lake Macquarie areas to about Wyong. There are records in Sydney at Botany Bay and around Port Jackson, but the species is rarely found here anymore and is considered extinct here. 

It grows in swampy heath and shrubland as well as moist dry sclerophyll woodland and forest, on sandy to clay soils.

It is a listed threatened species in the wild. (This editor has personally sampled sites, in the Lake Macquarie area, supporting several thousand plants which can really only be detected when flowering).

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, the leaves are alternate but are reduced to small and narrow triangular scales, to 3 mm long and to 5 mm wide, an unusual feature in this genus.

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 solitary to paired, white to pink to dark purple, to about 25 mm, occurring from July to December (chiefly spring).

Tetratheca spp. produce fruit as capsules which open longitudinally.

In this species, capsules are obovate to 8 mm long; with seeds to 4 mm long, brown in colour and with fine hairs

In the garden

This species is not known to be cultivated, likely due to its threatened status. Plants are likely unavailable currently for cultivation. It may be more readily cultivated in the future.

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

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.

Other information

This species is hard to spot when not in flower, especially when it is growing in habitats where its wiry and almost leafless stems are growing amongst other rushes and dense ground-layers.

Tetratheca comprises around 50 to 60 species, endemic to Australia. They occur in all states with the exception of the Northern Territory.

The flower colours have given rise to the common name for many species of “Black-eyed Susan”. However, note that this common name 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.

juncea – from Latin meaningrush-like” as in the species Machaerina juncea.

This species is listed as being threatened with extinction in the wild, at both the State and Commonwealth level with the category of Vulnerable.

NSW Flora online (PlantNET) Tetratheca juncea profile page:

https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Tetratheca~juncea

NSW Government Office of Environment and Heritage Tetratheca juncea profile page

https://www.environment.nsw.gov.au/threatenedspeciesapp/profile.aspx?id=10799

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

By Jeff Howes, edited Dan Clarke