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It grows mostly in NSW, with scant records in north-eastern Victoria; extending southwards from Sydney, through Wollongong and the Southern Highlands, down to west of Moruya and Narooma, with a disjunct patch around Eden and further south.
It grows in heath and dry sclerophyll forest on sandstone substrate.
Leionema spp. have characteristics matching those of other similar Rutaceae genera, (eg: Philotheca, Phebalium, Crowea); i.e., simple and alternate leaves, usually with oil glands.
In this species, leaves are usually shortly-cylindrical / needle-shaped (terete) or occasionally oval to lanceolate, to 20 mm long and to 4 mm wide, upper surface smooth or scabrous due to hairs with the lower surface having stellate (star-shaped) hairs; 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 branch terminals in compact heads, consisting of many flowers, with each flower up to 15 mm across, dark creamy-yellow in colour, with light-red tinges, occurring in spring.
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 about 4 mm long with an angled beak.
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.
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 18 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.
diosmeum – Latin – referring to the related genus, Diosma, which it is thought to resemble. Diosma is a genus of South African shrubs in the family Rutaceae with strongly odorous leaves.
This species is not considered to be at risk of extinction in the wild.
NSW Flora Online (PlantNET) – Leionema diosmeum profile page
https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Leionema~diosmeum
Wikipedia – Leionema and Leionema diosmeum profile page
https://en.wikipedia.org/wiki/Leionema
https://en.wikipedia.org/wiki/Leionema_diosmeum
Australian Native Plants Society Australia – Poor Relations – Phebalium / Leionema / Nematolepis