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Eucalyptus olsenii is known as the Woila Gum and grows into a tree reaching 12 metres in height.
It occurs purely in NSW, on the south coast / southern tablelands boundaries, mainly in Deua and Wadbilliga National Parks (roughly in the middle of a polygon created from Moruya to Bredbo to Cooma and to Bermagui).
It grows in dry sclerophyll woodland, often on sandy and rocky soils, on steep slopes.
The bark is rough on the lower part of the trunk whilst the rest of the trunk and branches are smooth, white, cream or grey.
Eucalyptus spp. have simple and usually alternate adult leaves with juvenile leaves starting off opposite to alternate (disjunct). In this species, juvenile leaves are ovate to lanceolate, to about 8 cm long and 4 cm wide, glossy green and discolorous. Adult leaves may be lanceolate or falcate, up to 12 cm long and 2 cm wide and glossy green.
The primary inflorescence of “eucalypts” (Angophora / Corymbia / Eucalyptus) is an umbellaster (an umbel-like cluster of flowers). In the flowers of Corymbia and Eucalyptus, the petals and sepals are fused into the distinctive calyptra / operculum (bud cap) which is shed when the flower opens (in some species, 2 bud caps (opercula) are shed). The flowers are conspicuously staminate – where many stamens are basically taking over the role of the petals, all surrounding one central carpel. In this species, buds are carried in umbellasters of seven and have distinctive ribs or ridges, as well as a white waxy coating, to 1.7 cm long with the opercula beaked or conical. Large white flowers are carried in spring and summer.
The fruit of eucalypts are a woody capsule (commonly called ‘gum nuts’) which come in a wide variety of shapes with the top part having a sunken, flat or raised disc and with the valves inserted, disc-level, exserted to strongly exserted. In this species, the woody fruits, are barrel or urn-shaped and 2 cm long (somewhat resembling those of a Corymbia sp).
Author’s notes:
In our cold climate garden (near Armidale, NSW) E. olsenii has proved tolerant of drought and frost, fast growing and free flowering. Our specimen flowered for the first time about four years after planting.
It is not widely planted but has attractive fruit, flowers and flower buds; and can likely be kept at less than 10 m tall in any garden through pruning. It grows naturally on sandy-rocky situations and so likely needs good drainage to thrive.
Plant in full sun for best results.
Propagate from seed
The common name refers to Mother Woila Mountain and Woila Creek, both locations in Deua National Park.
This species likely regenerates from the seed bank after fire. It may also produce epicormic shoots.
It is well-known that Eucalyptus is a large and diverse genus. Between 700 and 950 known species are reported, occurring as far north as The Philippines, as well as Indonesia, New Guinea, Timor and Australia. Only 16 species reportedly occur outside Australia. They occur in all Australian states. NSW currently has about 250 species. (See this website for some detailed information: https://apps.lucidcentral.org/euclid/text/intro/learn.htm).
Eucalyptus – from Greek, eu, “well” or “true” and calyptus, referring to the calyptra (καλύπτρo) or operculum, which is a bud cap or covering which covers the developing flowers. The calyptra is a fusion of petals and/or sepals and is shed when the flower opens, leaving a flower with many stamens (staminate) surrounding one female part (carpel).
olsenii – named after Ian Sinclair Olsen (b. 1943) who was a landscape designer at the Royal Botanic Gardens, Sydney and who has collected many plant specimens whilst bushwalking – in NSW, but also, Tasmania, Qld and SA. Olsen was the first to collect this species.
This species is not considered to be at risk of extinction in the wild but is considered rare with a limited natural distribution.
NSW Flora Online (PlantNET) – Eucalyptus olsenii profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Eucalyptus~olsenii
EUCLID – Eucalypts of Australia – Centre for Australian National Biodiversity Research – Eucalyptus olsenii profile page https://apps.lucidcentral.org/euclid/text/entities/eucalyptus_olsenii.htm
Wikipedia – Eucalyptus olsenii profile page https://en.wikipedia.org/wiki/Eucalyptus_olsenii
Arcane Botanica YouTube Channel (Dan Clarke) – Eucalypt Theory Video https://www.youtube.com/watch?v=m89bALPO4uc