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Zieria robusta

Round-leafed Zieria

Family: Rutaceae

An erect and dense shrub, growing to a height of 2.5 metres.

It has an interesting distribution with much disjunction; confined to NSW and Victoria; growing form the north-west near Coonabarabran, generally south-east to areas such as the very north-west of Wollemi NP, and south of Mudgee; east of Bathurst; then found in good numbers in Kanangra Boyd NP (south-west of Katoomba); with some scattered records west of Canberra and then north-eastern Victoria.

It is found generally on heath on rocky outcrops in mountainous areas.

The branches have ridges and warty protuberances and hairs.

Zieria spp. have leaves arranged in opposite pairs, compound with three leaflets (tri-foliolate) or one leaflet (uni-foliolate). When tri-foliolate, the leaflets are often similar in shape with the middle leaflet often larger, and with leaves usually strongly odorous, green to grey-green.

In this species, the leaves are mostly tri-foliolate, with obovate leaflets (wider end at the apex), to 12 mm long and to 6 mm wide, with a short point (mucro) and mostly hairless; upper surface dark green and lower surface paler; and with slightly crenate (rounded-toothed) margins.

Zieria spp. have flowers arranged in groups (cymose clusters) in the leaf axils and have four sepals joined at the base and four petals, alternating with the sepals. There are four stamens and four fused carpels.
In this species, the flowers are arranged in clusters of mostly 5 to 9 in leaf axils with the clusters usually longer than the leaves; white to pink, about 7 mm in diameter; occurring in spring and summer.

Zieria have a fruit described as a schizocarp-capsule which splits into segments called cocci (singular coccus).

Fruit generally have four cocci, each containing one or two seeds.

In this species, the cocci are dotted with oil glands and slightly rough, lacking an oil body (elaisome).

In the garden

This is another Zieria where not much is known about its cultivation potential. It likely needs more trialling and exposure. It grows naturally in rocky areas, likely on shallow soils but has a large range over NSW.

Many Zieria make interesting garden plants and deserve a place in gardens. They are a member of the Rutaceae family which include the genera Boronia, Philotheca and Crowea, all of which can be challenging to grow.

Some species are more commonly grown. They require good drainage, preferably on a light sandy soil and a semi-shaded area. They have soft foliage, can be pruned into nice-rounded shrubs and can flower prolifically.

Propagation

In common with most members of the Rutaceae, propagation from seed is difficult but cuttings usually strike readily from current season’s growth.

Other information

Zieria is a genus strongly odoriferous soft-woody shrubs, or small trees, with over 40 species described, all of which are endemic to Australia except for one species which is found in New Caledonia. They occur in all Australian states except Western Australia but the genus is under review and a number of species are yet to be described or the description published.

Zieria are similar to the better known genus Boronia but can be distinguished by the number of stamens in the flowers – four and eight in Boronia.

Most Zieria would die in a bushfire and regenerate from seeds. Suckering from roots may be possible.

Zierianamed in honour of Jan Zier (d. 1793), by Sir James E. Smith. Zier was a Polish botanist and cryptogam (ferns, mosses, lichen and fungi) specialist, for which there is little information online. He assisted Jacob Friedrich Ehrhart, the Director of the Botanical Garden of Hannover.

robusta is a Latin word meaning “robust”, “hard” or “strong” – possibly referring to where the plant grows naturally.

This species is not considered to be threatened with extinction in the wild.

NSW Flora Online (PlantNET) – Zieria robusta profile page

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

Wikipedia – Zieria and Zieria robusta profile pages

https://en.wikipedia.org/wiki/Zieria

https://en.wikipedia.org/wiki/Zieria_robusta

By Jeff Howes, edited Dan Clarke