Eucalyptus camaldulensis

River red gum
Eucalyptus camaldulensis in the Wonga Wetlands, NSW
Conservation status
Near Threatened  (IUCN 3.1)
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Myrtales
Family:	Myrtaceae
Genus:	Eucalyptus
Species:	E. camaldulensis
Binomial name
Eucalyptus camaldulensis Dehnh.

Eucalyptus camaldulensis, also called river red gum, is a flowering tree that grows only in Australia. It belongs to the myrtle family. This tree has smooth white or cream-colored bark, long narrow or curved leaves, flower buds grouped in sevens or nines, white flowers, and round fruit with parts that stick out above the edge. It is a well-known tree often found along rivers and streams in inland Australia. It gives shade in very hot places like central Australia.

Trunk and bark

Flower buds

Flowers

Fruit

Description

The tree usually grows about 20 metres (66 ft) tall but can sometimes reach 45 metres (148 ft). Its bark is smooth and white or cream with patches of yellow, pink, or brown. Near the bottom, the bark can be rough and loose. Young leaves are long and narrow, 80–180 mm (3.1–7.1 in) long and 13–25 mm (0.51–0.98 in) wide. Adult leaves are also long and narrow or curved, dull green or grey-green on both sides, and can be 50–300 mm (2.0–11.8 in) long and 50–300 mm (2.0–11.8 in) wide.

The flower buds grow in groups of seven, nine, or sometimes eleven. They are green to creamy yellow and have a pointed cap. The tree flowers mostly in summer, and the flowers are white. The fruit is a hard, round capsule that is 2 to 5 mm long and 4 to 10 mm wide, with parts sticking out above the edge. The flowers bloom for a long time during the year.

Branches or even whole trees can sometimes fall without warning. This makes camping or picnicking near river red gums dangerous, especially if the tree has dead branches or is weak.

Taxonomy

Eucalyptus camaldulensis was first officially described in 1832 by Friedrich Dehnhardt. He wrote about it in a book called "Catalogus Plantarum Horti Camaldulensis".

There are seven accepted subspecies of Eucalyptus camaldulensis. They differ mainly in the shape and size of the cap on the flower bud, how the stamens (flower parts) are arranged, and the number of veins in the leaves. The subspecies are:

• Eucalyptus camaldulensis subsp. acuta: has flower buds with a pointed cap 6–9 mm (0.24–0.35 in) long, straight stamens, and young leaves that are broad and lance-shaped or egg-shaped.
• Eucalyptus camaldulensis subsp. arida: has bluish-green adult leaves with few veins and flower buds with a curved or rounded cap 3–7 mm (0.12–0.28 in)long.
• Eucalyptus camaldulensis subsp. camaldulensis: has a strongly pointed cap, stamens that bend inward or irregularly, and narrow lance-shaped young leaves.
• Eucalyptus camaldulensis subsp. minima: has small flower buds with a cone-shaped cap 3–4 mm (0.12–0.16 in) long and broad young leaves usually covered with a powdery layer.
• Eucalyptus camaldulensis subsp. obtusa: has white, powdery bark at times and flower buds with a curved, cone-shaped cap 4–7 mm (0.16–0.28 in) long.
• Eucalyptus camaldulensis subsp. refulgens: has very shiny green adult leaves with many veins.
• Eucalyptus camaldulensis subsp. simulata: has a horn-shaped cap 9–16 mm (0.35–0.63 in) long.

The name "camaldulensis" comes from a private garden near the Camaldoli monastery in Naples, Italy, where Dehnhardt worked as the main gardener. The first plant used to describe the species was grown there from seeds collected near Condobolin, Australia, around 1817. This plant grew in the garden for about 100 years before being removed in the 1920s. A sample of this original plant (the holotype) is kept at the Natural History Museum of Vienna.

Although Dehnhardt was the first to describe Eucalyptus camaldulensis, his book was not well known. In 1847, another scientist named Diederich von Schlechtendal gave the tree a different name, Eucalyptus rostrata, but this name was not valid because it had already been used for another tree. In the 1850s, Ferdinand von Mueller called some river red gum trees Eucalyptus longirostris, and in 1856 Friedrich Miquel officially described this name. Finally, in 1934, William Blakely recognized Dehnhardt’s original name, and Eucalyptus camaldulensis became the accepted name for the river red gum tree.

Northern Territory Aboriginal names for this species are:

• aper (Alyawarr, Anmatyerr), aper or per (Eastern Arrernte), apere (Kaytetye), aylpele (Pintupi Luritja), itara, ngapiri, pipalya, yitara (Pitjantjatjara) apara, itara, piipalya, (Waramangu), kunjumarra (Warlpiri), kunjumarra and ngapiri (Western Arrernte).

Dimilan is the name of this tree in the Miriwoong language of the Kimberley.

Distribution and habitat

The dry river beds of central Australia have enough underground water for the trees.

The dry river beds in central Australia have enough underground water to keep the trees alive. Eucalyptus camaldulensis grows in more places naturally than any other eucalyptus tree. It is usually found near rivers and streams, and only a few places have these trees away from water.

• Subspecies acuta is common along rivers from south of Cape York Peninsula in Queensland to the northwest slopes and plains of New South Wales. It is not found near the coast or in dry inland areas.
• Subspecies arida is found in all mainland states except Victoria. It grows in dry areas but only where there is enough moisture under the soil.
• Subspecies camaldulensis is the main eucalyptus along the Murray-Darling river system and its smaller rivers. It also grows on the Eyre and Yorke Peninsulas, Kangaroo Island in South Australia, and some places along the Hunter River in New South Wales. It is the only subspecies found near the coast in Victoria.
• Subspecies minima grows only in South Australia, in the northern Flinders Ranges and northern Eyre Peninsula.
• Subspecies obtusa grows only in tropical northern Australia, including parts of the Kimberley, the Top End, and the Gulf of Carpentaria area, reaching as far east as the Gilbert River in Queensland.
• Subspecies refulgens grows only in the Pilbara-Gascoyne-Carnarvon region, along rivers that flow west, including some small rivers of the upper Murchison River.
• Subspecies simulata mostly grows along some rivers on Cape York Peninsula, with some groups further south.

In Victoria, this species can mix with Eucalyptus ovata, creating a hybrid called Eucalyptus ×studleyensis.

Eucalyptus camaldulensis grows in many climates, from tropical to temperate. It usually grows in places with 5 to 20 frosts in winter and very hot summers. Temperatures can range from −6–54 °C (21–129 °F), with daily changes up to 21 °C (70 °F).

Ecology

Eucalyptus camaldulensis growing beside the Edward River, NSW

Eucalyptus camaldulensis, also called river red gum, grows along rivers and on the flat land near rivers called floodplains. Because it lives near water, it often gets flooded. The tree likes soil that has clay in it. River red gums get water not only from rain but also from regular floods, which help fill the soil with water..

Because river red gums grow near water, they are a natural home for many animals, especially in dry areas. When the rivers flood, fish use the trees as places to breed. Birds that eat fish also benefit during their breeding season. Fallen branches from river red gums in rivers give fish places to hide and live. These fallen trees, called "snags," are very important for river life and help fish like the river blackfish. Sadly, many snags have been removed from rivers since the 1850s to make rivers safer for boats and to control flooding. But the Murray–Darling Basin Commission has said snags are important and has suggested stopping their removal from the Murray River.

When river red gums are about 120 to 180 years old, holes start to form in the tree. These tree hollows provide homes for many animals like bats, carpet pythons, and birds. The thick leaves of the tree give shade and shelter from the sun, especially in dry places.

The superb parrot, a bird that is in danger of disappearing, nests in river red gums.

River red gums help other animals by dropping leaves and insects, which provide food and nutrients. This is very important in places where the soil has few nutrients. Because they grow near rivers and floodplains, river red gums also help slow down floodwaters and stop soil from washing away.

Weed

Eucalyptus camaldulensis is considered a weed in some parts of the world like Portugal, the Canary Islands, South Africa, Spain, Bangladesh, the United States, Ecuador, and the Galapagos Islands. Even though it is native to some parts of Western Australia, it has spread to other places by escaping from gardens or being planted to help restore land. Because it can survive drought, salty soil, and produces many seeds, it grows easily and quickly. It is called invasive in places like South Africa, California, Jamaica, Spain, and Hawaii, and people work to control its spread there.

Reproduction and spreading

The flower starts as a small bud with a protective cap called the "operculum". This cap covers the inside of the flower while the male and female parts grow.

The male parts are called stamens. Each stamen has a thin stalk and a top part called the anther, which holds pollen. The anther opens up to release the pollen. During flowering, the stamens grow and surround the flower base.

The female parts are the ovaries, which hold the seeds. The ovaries are separated from the male parts by a disc. A part called the "style" grows from the ovaries up to the flower base, ending in the stigma, which catches pollen.

When the flower blooms, pollen from the anthers can fall on the stigma. Sometimes the flower can pollinate itself, but usually the stigma is ready only after the pollen is released. So, fertilization happens with pollen from other flowers on the same tree or from different trees. Insects, birds, and small animals help move pollen between flowers.

After flowering, the stamens fall off. The fruit grows from the fertilized flower. It becomes hard and woody. The fruit has triangular openings that let out yellow, cube-shaped seeds. Most seeds fall to the ground under the tree, but some are carried by wind or water. Seeds mostly spread in spring and summer, while natural flooding happens in winter and spring.

Since river red gums grow near water, it makes sense that floodwater helps spread seeds. But some studies show seeds sink after about 36 hours in water. Also, since seed spreading and flooding don’t always happen at the same time, it seems that wet soil and sunlight are more important for seeds to grow than floodwater spreading. Seeds that fall during floods don’t dry out, which helps them survive.

Even though many seeds are made, only a few grow into new trees. For a seed to grow well, there must be an open space in the forest so it can get enough sunlight.

Cultural importance

The river red gum tree is a well-known symbol of Australia. Its leaves have been shown on Australian stamps, and many people recognize it because it grows in many places. People also enjoy using the rivers and floodplains where the river red gum grows for seasonal fun and recreation.

In 1936, a picture of "The Old Gum Tree" was made into a stamp to celebrate 100 years since South Australia was founded.

Population management

The river red gum grows mostly near water, which has helped it survive and spread widely. Because of this, it is not considered endangered. But changes to its home can harm the tree and the animals that live with it. These changes include grazing by animals and controlling water for farming.

Grazing can stop new trees from growing because animals eat or step on young plants. But grazing can also help by clearing thick plants on the ground.

Water control causes two main problems. First, the timing of water flow changes. Second, natural flooding is reduced.

Water control lowers flooding in winter and spring and makes water flow more steady in summer and autumn. Since river red gums spread seeds in spring, less flooding can stop seeds from spreading by water, especially in floodplain forests. Also, some trees may stay flooded all the time because of dams or constant water flow, and seeds cannot grow in places that are always wet.

Less flooding means the soil under the floodplains does not get enough water. This can make trees grow weakly, die, or stop new seeds from growing. Without flooding, the river red gum’s home becomes less suitable for animals that need the trees for food and shelter. Some animals have already disappeared from river red gum areas in the Murray-Darling region.

Since the early 1980s, people have known that better water management can help keep river red gum forests healthy. This includes stopping extra water for farming, giving water permits, and flooding forests at the right times of the year.

In popular culture

Some famous river red gum trees are:

• The Big Tree near Moulamein, one of the largest river red gums in the Riverina, with a trunk 11.6 metres (38 ft) around.
• Cazneaux Tree, made famous by photographer Harold Cazneaux in his work "Spirit of Endurance".
• Separation Tree, where people celebrated when Victoria became a separate colony from New South Wales.
• The Old Gum Tree, where South Australia was officially started.
• The Queen’s Tree, planted in Kings Park, Perth, Western Australia, in 1954 by Queen Elizabeth II during her first visit to Australia.

Galleries

Features of the river red gum (Eucalyptus camaldulensis)

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  Adult leaves
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  Buds
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  Fruit
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  Seeds
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  Trunk bark

• Examples of river red gums
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  A river red gum near Bolin Bolin Billabong on the Yarra River.
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  A view down the Murray River where every tree pictured is a river red gum.
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  A 700-year-old tree at the Wonga Wetlands, NSW.
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  Many river red gums on the banks of the Barcoo River, south-west Queensland.
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  River red gums; the Murrumbidgee River in flood.
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  The Cazneaux Tree, near Wilpena Pound in Flinders Ranges National Park.
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  "The Queen's Tree", Kings Park, Perth, WA.
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  A river red gum in a bend of the Murrumbidgee River near Hay, NSW.
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  In Grampians National Park, Victoria.