Ficus rubiginosa

Ficus rubiginosa
Ficus rubiginosa
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Rosales
Family:	Moraceae
Genus:	Ficus
Species:	F. rubiginosa
Binomial name
Ficus rubiginosa Desf. ex Vent.
Range in Eastern Australia (in green)
Synonyms[1]
Ficus australis Willd. Ficus rubiginosa var. glabrescens F.M.Bailey Mastosuke rubiginosa (Vent.) Raf. Urostigma rubiginosum (Vent.) Gasp. Ficus rubiginosa var. lucida Maiden Ficus rubiginosa var. variegata Guilf. Ficus platypoda (Miq.) A.Cunn. ex Miq. Ficus sp. A (aff. rubiginosa) Urostigma leichhardtii Miq. Ficus leichhardtii var. angustata Miq. Ficus leichhardtii (Miq.) Miq. Ficus platypoda var. petiolaris Benth. Ficus platypoda var. subacuminata Benth. Ficus platypoda var. mollis Benth. Ficus macrophylla var. pubescens F.M.Bailey Ficus baileyana Domin Ficus shirleyana Domin

Ficus rubiginosa, commonly known as the rusty- or Port Jackson 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 classified in Ficus, a genus found worldwide in warm climates containing around 750 species, including the common fig (Ficus carica). Beginning life as a seedling, which grows on other plants (hemiepiphyte) or on rocks (lithophyte), Ficus rubiginosa grows to 30 m (100 ft) high and nearly as wide with a yellow-brown buttressed trunk. The oval glossy green leaves are anywhere from 4–19.3 cm (1 ¹⁄₂–7 ¹⁄₂ in) long and 1.25–13.2 cm (¹⁄₂–5 ¹⁄₄ in) wide.

The small round yellow fruit ripen and turn red at any time of year, although they peak in spring and summer. Known as a syconium, the fruit is an inverted inflorescence with the flowers lining an internal cavity. Ficus rubiginosa is exclusively pollinated the fig wasp species Pleistodontes imperialis, which may in fact comprise four cryptospecies. The syconia are also home to another 14 species of wasp, some of which induce galls while others parasitise the pollinator wasps, and at least 2 species of nematode. Many species of bird, including pigeons, parrots and various passerines, eat the fruit. The species' range spans the Australian east coast from Queensland through to Bega in southern New South Wales. The species grows in rainforest margins and rocky outcrops. It is used as a shade tree in parks and public spaces, and is well-suited for use as an indoor plant or in bonsai.

Taxonomy

The Port Jackson fig was described by French botanist René Louiche Desfontaines,^[2] from a type specimen whose locality is documented as "New Holland". In searching for the type specimen, Dale Dixon found one from the herbarium of Desfontaines at Florence Herbarium and one from the herbarium of Étienne Pierre Ventenat at Geneva. As Ventenat had used Desfontaines' name, Dixon selected the Florence specimen to be the type.^[3] The specific epithet rubiginosa related to the rusty coloration of the undersides of the leaves.^[4] Indeed, rusty fig is an alternate common name; others include Illawarra fig and Port Jackson fig.^[4] It was known as damun (pron. "tam-mun") to the local Eora and Darug inhabitants of the Sydney basin.^[5]

In 1806, German botanist Carl Ludwig Willdenow gave it the name Ficus australis in Species Plantarum,^[6] but this is a nomen illegitimum as the species already had a validly published name.^[1] Italian botanist Guglielmo Gasparrini, breaking up the genus Ficus in 1844 and placing the species in the genus Urostigma, as U. rubiginosum.^[7] In 1862, Friedrich Anton Wilhelm Miquel described Urostigma leichhardtii from material collected from Cape Cleveland, Queensland, noting it had affinities to F. rubiginosa.^[8] In 1867, he placed Urostigma as a subgenus in the reunited Ficus, which resulted in the taxon becoming Ficus leichhardtii. Miquel also described Ficus leichhardtii var. angustata from Whitsunday Island,^[9] later classified as F. shirleyana by Czech botanist Karel Domin.^[10] Frederick Manson Bailey described Ficus macrophylla var. pubescens in 1911 from Queensland, Domin later renaming it Ficus baileyana.^[11] All these taxa were found to be indistinguishable from (and hence reclassified as) F. rubiginosa.^[3]

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). They classified these species in a new series Rubiginosae in the subsection Platypodeae. Relationships are unclear and it is uncertain into which direction the group radiated (into rainforest or into arid Australia).^[12]

Joseph Maiden described variety lucida in 1902, while Bailey described var. glabrescens in 1913. Both botanists had diagnosed their varieties on the basis of their hairlessness. Maiden described a taxon totally devoid of hair while Bailey described his as nearly glabrous (hairless). As Bailey's description more closely matched Dixon's findings (that these variants were only partly and not completely hairless), Dale Dixon retained Bailey's name and reclassified it as Ficus rubiginosa forma glabrescens in 2001 as it differed only in the lack of hairs on new growth from the nominate form.^[3]

Description

Lithophytic Ficus rubiginosa growing on Narrabeen sandstone at Barrenjoey, New South Wales.

Ficus rubiginosa forms a spreading, densely-shading tree when mature, and may reach 30 m (100 ft) in height, although it rarely exceeds 10 m (30 ft) in the Sydney region.^[13] The trunk is buttressed and can reach 1.5 m (4 ft 11 in) in diameter, and the bark is yellow-brown.^[4] It can also grow as a hemiepiphyte,^[3] or 1–5 m (3–16 ft) high lithophyte.^[14] Alternately arranged on the stems, the ovate, obovate or oval-shaped leaves are anywhere from 4–19.3 cm (1 ⁵⁄₈–7 ⁵⁄₈ in) long and 1.25–13.2 cm (¹⁄₂–5 ¹⁄₄ in) wide, on 7–8.2 cm (2 ³⁄₄–3 ¹⁄₄ in)-long petioles. They are smooth or bear tiny rusty hairs. There are 16–62 pairs of lateral veins that run off the midvein at an angle of 41.5–84.0°, while distinct basal veins run off the midvein at an angle of 18.5–78.9°.^[3] Often growing in pairs, the figs are yellow initially and measure 4–10 mm (¹⁄₈–³⁄₈ in) across.^[15] Ripening to red in colour, they are tipped with a small nipple and on a 2–5 mm (¹⁄₈–¹⁄₄ in) stalk.^[13] Fruit ripen throughout the year, although there is a preponderance in spring and summer.^[4] Some trees have ripe and unripe fruit at the same time.^[15]

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.^[13] It is also confused with the small-leaved fig (F. obliqua), the syconia 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.^[3]

Distribution and habitat

Ficus rubiginosa occurs from the top of the Cape York Peninsula in north Queensland southwards along the eastern coastline of Australia to the vicinity of Bega on the south coast of New South Wales.^[13] It extends westwards to Porcupine Gorge National Park in Queensland and the far western plains in New South Wales.^[3] Both forms co-occur for most of the range, with the southernmost occurrence of f. glabrescens around the New South Wales-Queensland border. Lithophytic, hemiepiphytic and tree forms can be found in any given population.^[3]

Ficus rubiginosa is found in rainforest,^[3] rainforest margins, gullies,^[13] riverbank habitat, vine thickets,^[3] and rocky hillsides.^[13] It is found on limestone outcrops in Kanangra-Boyd National Park.^[16] Fig seedlings often arise in cracks in stone in cliffs and rock faces in natural environments,^[4] and in brickwork on buildings and elsewhere in the urban environment. The soils it grows on are often well drained and low in nutrients. They are derived from sandstone, quartzite and basalt. In the Sydney region, F. rubiginosa grows from sea level to 1000 m (3500 ft) altitude, in areas with an average yearly rainfall of 600-1400 mm.^[15] F. rubiginosa is largely sympatric with F. obliqua, though its range extends further west into dryer regions than the latter species.^[3]

Outside its native range, F. rubiginosa has naturalised to some degree in urban Melbourne and Adelaide in Australia, as well as New Zealand, Hawaii and California in the United States, and Mediterranean Europe.^[17] F. rubiginosa has been planted widely in Malta since the early 1990s but has not been observed to set fruit.^[18]

Ecology

Ficus rubiginosa in the Jardin Botanico Puerto de la Cruz in Tenerife

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).^[4] The spectacled flying-fox (Pteropus conspicillatus),^[19] and grey-headed flying fox (P. poliocephalus) eat the fruit.^[15] Many fruit drop onto the ground around the tree, though others are spread further afield by the animals that eat them.^[15]

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.^[20] Psyllids have almost defoliated trees in the Royal Botanic Gardens in Sydney in spring.^[15]

Reproduction and life span

As with all figs, the fruit is actually an inverted inflorescence known as a syconium, with tiny flowers arising from the inner surface.^[13] 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.^[21] Ficus rubiginosa is exclusively pollinated by a symbiotic relationship with Pleistodontes imperialis, a species of fig wasp.^[22] Biologist Eleanor Haine and colleagues analysed the DNA of the wasp across the fig's range and determined there are four cryptic lineages forming what they term the P. imperialis species complex. They diverge to a greater degree than some distinct wasp species, yet form a monophyletic group; this indicates that the wasp lineages have split without a change of host.^[17]

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.^[17] 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.^[22] Females then have a short time (< 48 hours) to find a tree with receptive syconia to successfully reproduce and disperse pollen.^[21]

A field study in Brisbane found that a F. rubiginosa trees often bore both male and female phase syconia at the same time,^{[lower-alpha 1]} 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.^[21]

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.^[23] P. imperialis has been transported to Hawaii, California and Israel and is pollinating its host in those places.^[22]

Trees can live to 100 years or more in age. They have been known to resprout after bushfire, bearing fruit within three years.^[15]

Other life in the syconia

The figs of F. rubiginosa—like those of many other Ficus species—also host other wasp species, which do not pollinate the fig. At least 14 species have been recorded,^{[lower-alpha 2]} of which four—two each belonging to the genera Sycoscapter and Philotrypesis—are common while others are rare. The community of wasps inside the syconium is made up mostly of pollinator wasps with much smaller numbers of these other species.^[14] Investigation of F. rubiginosa syconia found that the fig seeds and parasitic wasps develop closer to the wall of the syconium while pollinator wasps develop deeper in, presumably protected there from parasites. The parasitic wasps are around the same size as the pollinators and belong mainly to the genera Sycoscapter and Philotrypesis.^[24] Their larvae are thought to feed on the larvae of the pollinator wasp.^[14] Male Sycoscapter and Philotrypesis wasps fight other males of the same species when they encounter each other in a F. rubiginosa fig.^[25] Several genera of uncommon larger wasp species enter the immature figs before other wasps and induce galls, which may impact on numbers of pollinator wasps in the fig later. An example of this is Pseudidarnes minerva,^[14] a metallic green wasp species.^[26]

Nematodes of the genus Schistonchus are found in the syconia (and the pollinator wasps) of many species of fig. They appear to be less species-specific than wasps. S. altermacrophylla is generally associated with F. rubiginosa though it has been recorded on several other fig species.^[27]

Cultivation

As bonsai, Auburn Botanic Gardens

Ficus rubiginosa was first cultivated in the United Kingdom in 1789, where it is grown in glasshouses.^[28] It is commonly used as a large ornamental tree in eastern Australia, in the North Island of New Zealand,^[23] 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 on golf courses.^[29] Not as prodigious as other figs, F. rubiginosa is suited to slightly more confined areas, such as lining car parks or suburban streets. However, surface roots can be large and intrusive and the thin bark readily damaged when struck. Tolerant of acid or alkaline soils, it is hardy to US Zones 10B and 11, reaching 10 m (35 ft) high in 30 years. Planting trees 8-12 m (30-40 ft) apart will eventually result in a continuous canopy.^[30] The trees are of great value in providing fruit for birds and mammals, though drop large quantities of fruit and leaves, leaving a mess underfoot.^[28]

In a brief description, William Guilfoyle recorded a variegated fig from New South Wales "12-15 ft high" in 1911 as F. rubiginosa var. variegata.^[31] A variegated form is in cultivation on Australia's east coast,^[32] and in the United States.^[33] It is a chimera that is lacking in chlorophyll in the second layer of the leaf meristem.^[32] The leaves have an irregular central green patch along the midvein with irregular yellow and green elsewhere.^[28] Leaves that grow in winter generally have more green than those that do in summer. The chimera is unstable, and branches of all-green growth appear sporadically.^[32]

Despite the relatively large 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. Described as the best tree for a beginner to work with, it is one of the most frequently used native species in Australia.^[34] Its bark remains smooth, however, and does not attain a rugged, aged appearance. Known as "Little Ruby",^[35] a narrow-leaved form with its origins somewhere north of Sydney is also seen in cultivation.^[36]

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.^[37] It has gained the Royal Horticultural Society's Award of Garden Merit.^[38] It is easily propagated by cuttings or aerial layering.^[4]

The light-coloured wood is soft and brittle. Lightweight, it has some value in the making of such items as toys and small boxes.^[39]

Notes

References

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