Eucalyptus camaldulensis
Eucalyptus camaldulensis, commonly known as river red gum, is a flowering plant in the family Myrtaceae, and is endemic to Australia. It is a tree with smooth white or cream-coloured bark, lance-shaped or curved adult leaves, flower buds in groups of seven or nine, white flowers and hemispherical fruit with the valves extending beyond the rim. A familiar and iconic tree, it is seen along many watercourses across inland Australia, providing shade in the extreme temperatures of central Australia and elsewhere.
Description
Eucalyptus camaldulensis is a tree that typically grows to a height of but sometimes to and often does not develop a lignotuber. The bark is smooth white or cream-coloured with patches of yellow, pink or brown. There are often loose, rough slabs of bark near the base. The juvenile leaves are lance-shaped, long and wide. Adult leaves are lance-shaped to curved, the same dull green or greyish green colour on both sides, long and wide on a petiole long. The flower buds are arranged in groups of seven, nine or sometimes eleven, in leaf axils on a peduncle long, the individual flowers on pedicels long. Mature buds are oval to more or less spherical, green to creamy yellow, long and wide with a prominently beaked operculum long. Flowering mainly occurs in summer and the flowers are white. The fruit is a woody, hemispherical capsule long and wide on a pedicel long with the valves raised above the rim. The plant's flowers bloom for a long time throughout the year.The limbs of river red gums, sometimes whole trees, often fall without warning so that camping or picnicking near them is dangerous, especially if a tree has dead limbs or the tree is under stress.
Taxonomy and naming
Eucalyptus camaldulensis was first formally described in 1832 by Friedrich Dehnhardt who published the description in Catalogus Plantarum Horti Camaldulensis.Seven subspecies of E. camaldulensis have been described and accepted by the Australian Plant Census. The most variable character is the shape and size of the operculum, followed by the arrangement of the stamens in the mature buds and the density of veins visible in the leaves. The subspecies are:
- Eucalyptus camaldulensis subsp. acuta Ian Brooker & M.W.McDonald has mature flower buds with a pointed operculum long and erect stamens and broadly lance-shaped or egg-shaped juvenile leaves;
- Eucalyptus camaldulensis subsp. arida Ian Brooker & M.W.McDonald has bluish green adult leaves with only a few veins and mature flowers buds with a curved to rounded operculum long;
- Eucalyptus camaldulensis Dehnh. subsp. camaldulensis has a strongly beaked operculum, incurved or irregularly bent stamens and narrow lance-shaped juvenile leaves;
- Eucalyptus camaldulensis subsp. minima Ian Brooker & M.W.McDonald has mature flower buds that are small with a conical operculum long and broad juvenile leaves that are usually covered with a powdery bloom;
- Eucalyptus camaldulensis subsp. obtusa Ian Brooker & M.W.McDonald has white, powdery bark in some months and mature flower buds with a curved, conical operculum long;
- Eucalyptus camaldulensis subsp. refulgens Ian Brooker & M.W.McDonald has very glossy green adult leaves with a dense network of veins;
- Eucalyptus camaldulensis subsp. simulata Ian Brooker & Kleinig. has a horn-shaped operculum long.
Although Dehnhardt was the first to formally describe E. camaldulensis, his book was largely unknown to the botanical community. In 1847 Diederich von Schlechtendal gave the species the name Eucalyptus rostrata but the name was illegitimate because it had already been applied by Cavanilles to a different species. In the 1850s, Ferdinand von Mueller labelled some specimens of river red gum as Eucalyptus longirostris and in 1856 Friedrich Miquel published a description of von Mueller's specimens, formalising the name E. longirostris. Finally in 1934, William Blakely recognised Dehnhardt's priority and the name E. camaldulensis for river red gum was accepted.
Northern Territory Aboriginal names for this species are:
- aper, aper or per, apere, aylpele, itara, ngapiri, pipalya, yitara 'apara, itara, piipalya,, kunjumarra, kunjumarra and ngapiri.
Distribution and habitat
Eucalyptus camaldulensis has the widest natural distribution of any eucalyptus species. It is commonly found along waterways and there are only a few locations where the species is found away from a watercourse.- Subspecies acuta is common along rivers from south of Cape York Peninsula in Queensland to the north west slopes and plains of New South Wales but is absent from coastal areas and the arid inland.
- Subspecies arida has the widest distribution of the subspecies and is found in all mainland states except Victoria. It grows in arid regions but only where there is sufficient subsoil moisture.
- Subspecies camaldulensis is the dominant eucalypt along the Murray-Darling river system and its tributaries. It also occurs on the Eyre and Yorke Peninsulas and Kangaroo Island in South Australia and in some locations along the Hunter River in New South Wales. It is the only subspecies in coastal Victoria.
- Subspecies minima is endemic to South Australia, where it grows in the northern Flinders Ranges and the northern Eyre Peninsula.
- Subspecies obtusa is endemic to tropical northern Australia, including parts of the Kimberley, the Top End and the Gulf of Carpentaria hinterland as far east as the Gilbert River, Queensland in Queensland.
- Subspecies refulgens is endemic to the Pilbara-Gascoyne-Carnarvon region, along rivers flowing westwards, including along some of the tributaries of the upper Murchison River.
- Subspecies simulata is mainly restricted to some rivers on Cape York Peninsula, but with some populations further south.
Eucalyptus camaldulensis grows under a wide range of climatic conditions from tropical to temperate, but the main areas are characterised by 5 to 20 frosts in winter and high summer temperatures. Temperature conditions may vary from a minimum of -6°C to a maximum of 54°C with a diurnal range up to 21°C.
Ecology
The species can be found along the banks of watercourses, as well as the floodplains of those watercourses. Due to the proximity to these watercourses, river red gum is subject to regular flooding in its natural habitat. River red gum prefers soils with clay content. The trees not only rely on rainfall but also on regular flooding, since flooding recharges the sub-soil with water.The association of the river red gum with water makes the tree a natural habitat choice, indeed sometimes the only choice in drier areas, for other species. The trees provide a breeding habitat for fish during the flooding season, which also benefits aquatic bird life that depend on fish as a food source during their own breeding season. Wilson, who examined the management of river red gums in NSW, suggests shelter is provided for fish in rivers and streams by fallen branches from the river red gum. The "snags" formed when river red gums fall into rivers such as the Glenelg, are an important part of river ecosystems, and vital habitat and breeding sites for native fish like river blackfish. Unfortunately most snags have been removed from these rivers, beginning in the 1850s, due to river-improvement strategies designed to prevent hazards to navigation, reduce damage to in-stream structures, rejuvenate or scour channels, and increase hydraulic capacity to reduce flooding. However, the Murray–Darling Basin Commission has recognised the importance of snags as aquatic habitat, and a moratorium on their removal from the Murray River has been recommended.
Hollows start to form at around 120–180 years of age, creating habitat for many wildlife species, including a range of breeding and roosting animals such as bats, carpet pythons, and birds. The dense foliage of the tree also provides shade and shelter from the sun in drier areas.
The superb parrot, a threatened species, is amongst the bird species that nest in the river red gum.
River red gums contribute to the provision of nutrients and energy for other species through leaf and insect fall. This is especially important to the ecology in areas of low nutrients. The tree's preferred habitat of floodplains and watercourses also gives it the role of flood mitigator, which slows silt runoff.