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Boronia rubiginosa

Family: Rutaceae

A shrub to a height of 2 metres.

It is endemic to New South Wales, growing as far south as west of Berrima, with disjunct records up into Sydney and north-west Sydney (Wisemans Ferry to Kurrajong), then with gaps to Lithgow-Kandos area, north into Goulburn River National Park (Lees Pinch). There are also a few disjunct records in Mt Kaputar National Park (although these may be Boronia ruppii – see notes below).

It grows in dry sclerophyll shrubland, woodland and forest on skeletal sandstone-derived soils.

It has branchlets with stellate-rusty hairs.

Boronia 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 the leaves are compound-pinnate to about 50 mm long and to 35 mm, with 3 to 7 leaflets (to 30 mm long and to 12 mm wide), with the lower surface markedly paler, hairless to stellate-hairy.

Boronia 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, which makes them easily identifiable in NSW bushland.

In this species, flowers are arranged in leaf axils solitarily or in groups or 2 to 3, pale to bright pink and with woolly hairs, occurring from July to November.

The fruit of Boronia 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, about 4 mm long and 2 mm wide.
Not much is known currently about the cultivation of this species and it is not commonly grown. It may be that it is difficult to grow or has not been trialled sufficiently to verify cultivation potential. It may become more readily cultivated in the future. It is a very nice plant in full flower and so would benefit any garden.

In the garden

Growing boronias 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.

Most boronias have a short life span of two to three years in a garden situation but are a rewarding plant while healthy as they provide lovely fragrance and flowers in Spring

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.

Planting 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.

Propagation

Boronias can be propagated from cuttings, but overall you will have limited success with most but not all species.

Other information

Boronia is a genus of about 160 species of flowering plants in the citrus family Rutaceae. Most species are endemic to Australia and species can be found in all states. There are also some species in New Caledonia, which were previously placed in the genus Boronella.

This species used to be included in a broader definition of Boronia ruppii which grows on serpentite in the Barraba / Mt Kaputar area.

Boronias are likely killed by fire and regenerate from the seedbank.

Boronia – after Francesco Borone (1769-1794), an 18th century Italian botanist who assisted John Sibthorpe. Allegedly, he died at age 25, due to falling out a window whilst collecting plant specimens.
rubiginosa – is a Latin word meaning “rusty”, referring to the stellate hairs on the branchlets and flowers.

This species is not considered to be at risk of extinction in the wild.

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

Wikipedia – Boronia rubiginosa and Boronia profile pages
https://en.wikipedia.org/wiki/Boronia
https://en.wikipedia.org/wiki/Boronia_rubiginosa

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

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

By Jeff Howes