Desf. ex Vent.
Ficus rubiginosa, the rusty fig, Port Jackson fig, or little-leaf fig (damun in the Sydney language) is a species of flowering plant in the family Moraceae that is native to eastern Australia. It is a banyan of the genus Ficus which contains around 750 species worldwide in warm climates, including the common fig (Ficus carica).
Ficus rubiginosa forms a spreading densely shading tree when mature, and may reach 30 m (98 ft) in height, although it rarely exceeds 10 m (33 ft) in the Sydney region. The trunk is buttressed and can reach 1.5 m (4 ft 11 in) in diameter, and the bark is yellow-brown. Its ovate to oval-shaped leaves are 6–10 cm (2–4 in) long on 1–4 cm (0.4-1.6 in) petioles. Often growing in pairs, the figs are yellow ripening to red in colour, tipped with a small nipple and on a 2–5 mm stalk. Fruit ripen throughout the year, although there is a preponderance in spring and summer.
It closely resembles its relative the Moreton Bay fig (F. macrophylla). Having similar ranges in the wild they are often confused. The smaller leaves, shorter fruit stalks, and rusty colour of the undersides of the leaves of the Port Jackson fig are the easiest distinguishing features. It is also confused with the small-leaved fig (F. obliqua), the synconia of which are smaller, measuring 4.3–11.9 mm long and 4.4–11.0 mm in diameter, compared with 7.4–17.3 mm long and 7.6–17.3 mm diameter for F. rubiginosa.
In tropical and humid climates, the lower branches of the Port Jackson fig may form aerial roots which strike root upon reaching to the ground, forming secondary root systems. This process is known as banyaning after the banyan tree of which it is a characteristic.
Distribution and habitat
Ficus rubiginosa occurs from north Queensland southwards along the eastern coastline of Australia to the vicinity of Bega on the south coast of New South Wales. It is found on the edges of rainforest and gullies and rocky hillsides. It is found on limestone outcrops in Kanangra-Boyd National Park. Fig seedlings often arise in cracks in stone in cliffs and rock faces in natural environments, and in brickwork on buildings and elsewhere in the urban environment.
As with all figs, the fruit is actually an inverted inflorescence known as a syconium, with tiny flowers arising from the inner surface. Ficus rubiginosa is monoecious — both male and female flowers are found on the same plant, and in fact in the same fruit although they mature at different times. Ficus rubiginosa is pollinated by a symbiotic relationship with a fig wasp species (Pleistodontes imperialis). The fertilised female wasp enters the receptive 'fig' (the syconium) through a tiny hole at the crown (the ostiole). She crawls around the inflorescenced interior of the fig, pollinating some of the female flowers. She then lays her eggs inside some of the flowers and dies. After several weeks' development in their galls, the male wasps emerge before the females. They chew holes in the galls containing females and fertilise them through the hole they have just chewed. Males return later to mated females, and enlarge the mating holes to enable the females to emerge. Some males then chew their way through the syconium wall, which allows the females to disperse after collecting pollen from the now fully developed male flowers. Females then have a short time (< 48 hours) to find a tree with receptive syconia to successfully reproduce and disperse pollen.
A field study in Brisbane found that a F. rubiginosa trees often bore both male and female syconia at the same time, which could be beneficial for reproduction in isolated populations. The same study found that male phase syconia development persisted through the winter, showing that its wasp pollinator tolerated cooler weather than those of more tropical fig species. F. rubiginosa itself can endure cooler climates than other fig species.
Pleistodontes imperialis traversed the waters between Australia and New Zealand some time between 1960 and 1972, and seedlings of the previously infertile trees of F. rubiginosa began appearing in brick and stone walls, and on other trees, particularly in parks and gardens around Auckland. They have been recorded as far south as Napier.
The fruit is consumed by many bird species including the rose-crowned fruit-dove (Ptilinopus regina), wompoo fruit-dove (P. magnificus), wonga pigeon (Leucosarcia melanoleuca), topknot pigeon (Lopholaimus antarcticus), Australasian figbird (Sphecotheres vieilloti), green catbird (Ailuroedus crassirostris), regent bowerbird (Sericulus chrysocephalus), satin bowerbird (Ptilonorhynchus violaceus), pied currawong (Strepera graculina), and Pacific koel (Eudynamys orientalis). The spectacled flying-fox (Pteropus conspicillatus) eats the fruit.
The thrips species Gynaikothrips australis feeds on the underside of new leaves of F. rubiginosa, as well as F. obliqua and F. macrophylla. As plant cells die, nearby cells are induced into forming meristem tissue and a gall results, and the leaves become distorted and curl over. The thrips begin feeding when the tree has flushes of new growth, and the life cycle is around six weeks. At other times, thrips reside on old leaves without feeding. The species pupates sheltered in the bark. The thrips remain in the galls at night and wander about in the daytime and return in the evening, possibly to different galls about the tree.
The Port Jackson fig was described by French botanist René Louiche Desfontaines. Its specific epithet rubiginosa related to the rusty coloration of the undersides of the leaves. Indeed, rusty fig is an alternate common name; others include Illawarra fig and Port Jackson fig. It was known as damun (pron. "tam-mun") to the local Eora and Darug inhabitants of the Sydney basin.
In a study published in 2008, Nina Rønsted and colleagues analysed the DNA sequences from the nuclear ribosomal internal and external transcribed spacers (ITS and ETS), and the glyceraldehyde-3-phosphate dehydrogenase (G3pdh) region, in the first molecular analysis of the section Malvanthera. They found F. rubiginosa to be most closely related to the rainforest species F. watkinsiana and two lithophytic species of arid northern Australia (F. atricha and F. brachypoda) and classified it in a new series Rubiginosae in the subsection Platypodeae. Relationships are unclear and it is uncertain which direction the group radiated (into rainforest or into arid Australia).
Ficus rubiginosa is commonly used as a large ornamental tree in eastern Australia, in the North Island of New Zealand, and also in Hawaii and California, where it is also listed as an invasive species in some areas. It is useful as a shade tree in public parks and golf courses. Despite the size of the leaves, it is popular for bonsai work as it is extremely forgiving to work with and hard to kill; the leaves reduce readily by leaf-pruning in early summer. It has been described as the best tree for a beginner to work with, and is one of the most frequently used native species in Australia. A narrow leaved form with its origins somewhere north of Sydney is also seen in cultivation.
Ficus rubiginosa is also suited for use as a houseplant in low, medium or brightly lit indoor spaces, although a variegated form requires brighter light. It has gained the Royal Horticultural Society's Award of Garden Merit.
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