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Cyanothamnus quadrangulus

Narrow-leaved Boronia

Family: Rutaceae

A small shrub growing to 1 metre tall by up to 1 metre wide with square / 4-angled branches.

It occurs over large parts of NSW, growing from as far south as near Wadbilliga National Park (south-east of Cooma), extending north in sporadic patches near Nowra, extending through the western parts of Sydney (Blue Mountains / Wisemans Ferry), the Hunter Valley, out to Dubbo and through the northern tablelands and north-coast, just into south-east Queensland.

It is typically found in heath and dry sclerophyll woodland and forests, on sandstone ridges and rocky slopes.
Cyanothamnus spp. produce opposite leaves which can be simple or compound (sometimes on the same plant) and are usually aromatic (sometimes strongly-so). In this species, leaves are compound-bipinnate (jacaranda-type structure) with 3 to 5 pinnae (groups of leaflets) with each pinna having pairs of two leaflets, ending in 3 leaflets at the terminals. Overall, leaves are up to 40 mm long, with each leaflet linear to elliptic in shape, to 15 mm long and 2 mm wide, with glands (glandular warts) and aromatic when crushed.

Cyanothamnus have complete flowers (bisexual and with all whorls present). The flowers are produced either solitarily or in groups, in the leaf axils, or, at the branch terminals. There are usually four sepals, four petals and generally eight stamens, surrounding one female part (carpel). Flowers are often pink to purple or blue, which makes them easily identifiable in NSW bushland.

In this species, flowers are white to pale pink and are produced in leaf axils, mainly in groups of up to 15, occurring from April to October.

The fruit of Cyanothamnus are described as a schizocarp-capsule; a capsule that splits into even segments, which each segment called a coccus. In this species, the capsules are glabrous, 2.5 to 4 mm long and about 2 mm wide

In the garden

There is not much currently known about the cultivation of this particular species. It may be difficult to grow or has not had enough effort applied to verify it can be cultivated. It may be more readily propagated in the future.

Growing boronias (including Cyanothamnus) can be a frustrating experience and they have a reputation for being difficult. Their attractiveness has led to substantial efforts to cultivate them. One tip is to try to grow forms that are local to your area, rather than attempting to grow those species from interstate. There are certainly some species that have proven easier to grow than others.

For them to grow at their best, select a position with dappled sunlight and especially protection from hot afternoon sun in summer, as well as from wind, which they dislike.

The soil must be well drained and have an even supply of moisture. If they dry out, they will surely die. Plating on a slight slope is said to work well.

For a longer life, the best way to grow them is in a medium sized pot, say 30 cm in diameter where drainage and moisture can be controlled. A sheltered patio or courtyard that receives at least a few hours sunlight a day would be ideal

Fertilise after flowering.

The conventional wisdom is, think deeply about which species to plant and the location to plant it.
Boronias (including Cyanothamnus) can be propagated from cuttings but with limited success with most but not all species.

Propagation

Other information

This species, until 2020, went by the name Boronia anethifolia. It has also previously been called Boronia anemonifolia var. anethifolia

This species has been moved to the closely related genus Cyanothamnus.

As the name Cyanothamnus anethifolius had already being used and published for a different taxon (which is now Cyanothamnus ramosus), this species has been renamed Cyanothamnus quadrangulus.

Most Cyanothamnus species would die in a fire and likely regenerate from the seedbank.

Cyanothamnus – cyano from Ancient Greek. kuáneos meaning “dark blue” and -thamnus (Θάμνος) meaning “bush” or “shrub” – referring to many species in the genus having blue flowers.
quadrangulus – Latin – meaning “four-angled” or “square” and refers to the square-like stems of this species.

Not considered at risk in the wild.

Australian Native Plants Society Australia – Boronia profile page
http://anpsa.org.au/boronia9.html

Gardening with Angus Website – Boronia for Beginners
https://www.gardeningwithangus.com.au/boronias-for-beginners-2/

Wikipedia – Cyanothamnus quadrangulus profile page
https://en.wikipedia.org/wiki/Cyanothamnus_quadrangulus

NSW Flora Online (PlantNET) – Boronia anethifolia profile page
https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Boronia~anethifolia

By Jeff Howes, edited Dan Clarke