River red gum

Appearance

''Eucalyptus camaldulensis'' is a tree that typically grows to a height of 20 metres but sometimes to 45 metres 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, 80–180 mm long and 13–25 mm wide. Adult leaves are lance-shaped to curved, the same dull green or greyish green colour on both sides, 50–300 mm long and 7–32 mm wide on a petiole 8–33 mm long.

The flower buds are arranged in groups of seven, nine or sometimes eleven, in leaf axils on a peduncle 5–28 mm long, the individual flowers on pedicels 2–10 mm long. Mature buds are oval to more or less spherical, green to creamy yellow, 6–9 mm long and 4–6 mm wide with a prominently beaked operculum 3–7 mm long.

Flowering mainly occurs in summer and the flowers are white. The fruit is a woody, hemispherical capsule 2–5 mm long and 4–10 mm wide on a pedicel 3–12 mm long with the valves raised above the rim.

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.

Naming

''Eucalyptus camaldulensis'' was first formally described in 1832 by Friedrich Dehnhardt who published the description in ''Catalogus Plantarum Horti Camaldulensis''.

Distribution

''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.

Reproduction

The flower begins as an "invaginated receptacle". The operculum, or cap, protects the interior of the flower bud, as the male and female parts develop.

The male parts of the flower consist of the stamen, a slender filament, and the anther, two pollen sacs located at the top of the stamen. The anther sacs open into longitudinal slits to release their pollen. These filaments will extend to encircle the receptacle during flowering.

The female parts of the flower, the ovaries, are contained in ovary chambers. These chambers are separated from the receptacle containing the male parts by a disc. From the top of the ovaries a structure called the style extends into the receptacle, to form the stigma.

During flowering, pollen from the anthers can fall onto the stigma. This can occasionally lead to self-pollination, although the stigma does not become receptive until a few days after the operculum has been detached by the expanding stamens, and the flower's pollen has already been released. Fertilisation will therefore occur with other flowers on the same tree or other flowers on a different tree. Insects, birds, and small mammals help in the pollination of other flowers.

After flowering, the stamens will detach. The fruit is the part of the flower that remains after fertilisation, which enlarges, dries, and becomes woody. Triangular valves in the fruit will open, dispersing yellow, cuboid seeds. When seeds are shed from a tree, most fall onto the ground below the crown, with some seed carried by the wind and water. Dissemination occurs mostly in spring and summer, while natural flooding occurs during winter and spring. As the tree is inextricably linked with waterways, seed dispersion would logically be facilitated by floodwater. There is some contention in this theory, however, where the CSIRO describes an experiment that demonstrated seeds were found to sink after only 36 hours. It would also seem that as the seeding and flooding do not entirely coincide, it could be inferred that the conditions for germination, such as damp soil and plenty of sunlight, are more important in the continuation of the species than seed dispersal by means of floodwater.

Seeding during the flooding season would prevent desiccation of the seed, which is the main cause of a seed's failure to reproduce. Despite this apparent evolutionary advantage of the species living near watercourses to avoid seed desiccation, many seeds will be produced within an ''E. camaldulensis'' forest before one will grow to its own reproducing stage. A gap in the forest must be available for the germinated seed to receive adequate sunlight.

Cultural

''E. camaldulensis'' readily germinates from both fresh seed and seed stored in cool dry conditions. It quickly toughens up and can withstand drought even whilst in forestry tubes. It makes an excellent bonsai and will readily regrow both from the base and from epicormic buds.Examples of river red gums include:
⤷  The Big Tree near Moulamein - one of the largest river red gums in the Riverina, with a circumference of 11.6 metres;
⤷  Cazneaux Tree - Photographed by Harold Cazneaux in the ''Spirit of Endurance'';
⤷  Separation Tree - Where celebrations were held when Victoria became a separate colony to New South Wales;
⤷  The Old Gum Tree - Where the colony of South Australia was proclaimed;
⤷  The Queen's Tree - Planted in Kings Park, Perth Western Australia in 1954 by Her Majesty Queen Elizabeth II on her first visit to Australia.