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A shrub to 2 metres high with prominent warts on stems and small stellate hairs.
It has a very restricted distribution, growing in NSW only, along the Colo River and connected waterways, from around Upper Colo into Wollemi National Park.
It grows in riparian areas, in sand amongst sandstone boulders, sometimes in thickets dominated by Tristaniopsis laurina (water Gum) and Backhousia myrtifolia (Grey Myrtle).
It is a rare species in NSW but can be seen in high numbers in its habitat.
Leionema spp. have characteristics matching those of other similar Rutaceae genera, (e.g. Philotheca, Phebalium, Crowea); i.e., simple, alternate leaves, usually with oil glands.
In this species, leaves are linear to oblanceolate, to 35 mm long and to 3 mm wide, with a tapering point, dark green.
Leionema spp. have 5-merous flowers; i.e. 5 sepals, 5 petals and usually 10 stamens surrounding 5 carpels, with an overall attractive star-shaped appearance. Flowers can be produced in leaf axils or branch terminals, in cymose clusters or solitary.
In this species, the inflorescences are produced at the terminals (though hardly exceeding the leaves), with up to 20 flowers per cluster; each flower to 10 mm across and brilliant white, with pale green colouring outside, with the odd flower having 6 petals.
The fruit of Leionema is a schizocarp-capsule – which splits into equal segments on maturity which each segment called a coccus (plural cocci).
The fruits are to 4 mm long to 3 mm wide with the seed black to dark brown, approximately 3 mm long x 2 mm wide; smooth and shiny.
This species is not widely known to be cultivated. It may be difficult to grow or may not have been trialled sufficiently. Check with local native nurseries for availability. There are photos of it online growing in mulched garden beds and it appears very attractive.
In cultivation, Leionema spp. prefer well drained (sandy to sandy loams), acidic soils in dappled shade or morning-light positions. They are highly-drought tolerant once established but benefit from some supplementary watering. It is advised to add some slow-release fertiliser when first planted and they will benefit from periodic organic fertilising (eg: blood and bone or seaweed solution).
It has been reported that species in this genus should be cultivated more widely and simply need more attention and effort (see Australian Native Plants Society Australia weblink in the references).
In common with most members of the Rutaceae, propagation from seed is difficult but cuttings usually strike readily.
Leionema are a genus of 28 known species, 27 of which are endemic to Australia, with 1 species endemic to New Zealand. NSW currently has 15 species.
These species have been previously classified in the genus Eriostemon and Phebalium. Leionema differs by not having anthers with an apical point or gland, as well as free sepals on the flowers and small bracteoles on the middle to upper part of flower stalks (pedicels).
Most Leionema spp. would likely die in a fire and regenerate from seed. Some basal regrowth or stem-reshooting may be possible.
Leionema – from Greek leios (λείος), meaning “smooth”, and nema (nήμα), a thread, referring to a ‘hilar strand’; a small piece of tissue joining the hilum (a scar on the side of the seed) to the ovule.
praetermissum – Latin meaning “omitted”, or “overlooked” which refers to the fact that this species remained informally described, after discovery, for at least 30 years. A description was published in 2019.
This species is not considered to be at risk in the wild but has a restricted distribution and is considered rare.
NSW Flora Online (PlantNET) – Leionema praetermissum profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Leionema~praetermissum
Wikipedia – Leionema and Leionema praetermissum profile page https://en.wikipedia.org/wiki/Leionema