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| Australia | ||
| SECTION 1 part 1 part 2 part 3 part 4 SECTION 2 SECTION 3 SECTION 4 |
 AUSTRALIA, the
world's largest island, has a land area of just over 2.9 million square miles, two-fifths
of which lies north of the Tropic of Capricorn. It has been isolated for at least 50
million years and 85 % of its unique flora is endemic. Although perhaps best known for its
deserts, Australia has a wide diversity of climate and landscape which gives rise to a
broad range of vegetation types, particularly in the coastal areas. In the north and
north-east the coastal areas have a tropical climate with distinct wet and dry seasons,
the summer (November to March) being the wettest time of the year. These coastal areas
support rain forest and mangrove swamps with woodland and savannah inland. The south-west
and south-eastern areas of Australia have a temperate to subtropical climate with rainfall
throughout the year. Their natural vegetation is mixed woodland and Eucalyptus scrub known as I mallee'. An alpine
flora grows at higher altitudes in the mountains in the south-east. Much of the vast area
of central Australia is dry throughout the year, and rather few plants grow there in the
stunted Acacia scrub. There are
estimated to be about 110 genera and over 700 species of orchids native to Australia.
Forty per cent of the species are epiphytic or lithophytic and grow in the tropical
northern and north-eastern regions. Only five epiphytic species occur as far south as
Victoria. The 60% of Australian orchids which grow terrestrially are found mainly in the
south-west and south-east of the country and are nearly all endemic. The Kew orchid
collection has many representatives both of terrestrial and epiphytic orchids from
Australia. Temperate Terrestrials The
Australian temperate terrestrials deserve to be much better known and more widely
cultivated in Britain. Like the European terrestrials they grow in a symbiotic
relationship with a mycorrhizal fungus which obtains organic matter from the compost and
provides the orchid with nutrients. The annual
growth cycle at Kew starts at the end of October, when the first green shoots of Pterostylis plants appear. The early flowering
species such as P. angusta and P. nutans quickly put up flower spikes. Gradually the
leaves of Diuris species start to show through, D. palustris being the first to flower, at the end of
January. By this time the first Caladenia leaves
are growing. After flowering, by about mid-May, the plants die down and the tubers remain
dormant through the summer when repotting is done. Dormant
tubers are removed from the old pots, but a third of the old compost is retained and
incorporated in the new compost. This ensures an adequate supply of mycorrhizal fungus for
the orchid to make vigorous growth. Some species increase readily in cultivation by
forming up to five new tubers on stolons which can be divided when repotting. Many of the
Pterostylis species can be propagated in this way, whereas most of the caladenias produce
just one new tuber to replace the old one and so can only be increased from seeds. Tubers
are repotted 3 cm below the surface of the compost with about 2 cm space between each one
and then watered in. Normally another watering is not needed until the first shoots are
growing. Watering is controlled according to the known habitat of the orchid in the wild.
Diuris palustris, for example, grows in marshy areas and so is watered freely, while
Thelymitra antennifera, which grows in dry areas, is kept just moist but watered
infrequently. The genus
Pterostylis contains about 100 species, of which 15 are currently grown at Kew. The green
hoods, as they are commonly known, are among the easiest of the Australian temperate
terrestrials to maintain in cultivation. The genus is characterised by the hood which is
formed by the fusion of the dorsal sepal and lateral petals of the flower. The hood is
usually green, streaked with white, red or brown in different species. Like many orchids,
Pterostylis flowers have evolved a complex method of achieving pollination. The lip of the
flower is hinged, and when an insect, normally a small gnat, lands upon it, the lip
springs backwards against the column trapping the insect inside the flower. The insect
climbs up the column, gripping the conveniently placed hairs and squeezes out of the gap
at the top. In doing so it brushes against the pollinia, which adhere to the insect as it
takes flight. Landing on the lip of another flower, the insect is again trapped when the
lip springs back. The pollinia which it has carried from the previous flower stick to the
stigmatic surface as the insect climbs the column. As it gains its freedom again, it flies
off with a fresh set of pollinia from that flower. The
readiness of the spring in the lip of a Pterostylis flower can easily be tested by
touching it with a pencil. Usually the lip flies back straight away. The largest
species of Pterostylis is P. baptistii, the king green hood, which grows up to 40 cm tall
with a hood up to 6 cm long. In Australia it grows in large colonies in the dense scrub
surrounding streams and marshes. It has a translucent flower with green veins and brown
markings at the tip of the hood. The hood is held erect. In P. nutans, the nodding green
hood, the flower is bent over facing the ground. Most Pterostylis species bear a single
flower at the top of the flowering shoot, but a few are multiflowered. Pterostylis vittata
is one of this group and has up to eight green-veined flowers on each stem. It grows
naturally in the light scrub close to the southern coast of the country. The genus
Diuris, commonly called donkey orchids or double tails, is almost completely confined to
Australia, with just one species found elsewhere - Diuris fryana is endemic to Timor.
Diuris carinata, D. palustris and D. emarginata all grow in damp areas while most other
species occur in grassland or open woodland. It is thought that some Diuris species have evolved flower shapes and
colours which mimic those of leguminous shrubs in order to attract insects to pollinate
them. There are
about 50 species of Corybas, worldwide, ranging
from the Himalayan foothills, through Malaysia to New Zealand, and 20 species are found in
Australia. Corybas species grow in damp
sheltered mossy areas under low bushes or ferns. They have a reputation for not flowering
well in cultivation; and the partly formed flowers will abort if they are in a cold
draught. To prevent this happening, Corybas plants
are always grown in a sheltered spot in the greenhouse, under the shade of leaves of other
plants. If kept in too much light their leaves become yellowish, and if in too much shade
they stand rather unnaturally high above the surface of the compost. About 75% shade is
most suitable. When conditions are right their fascinating flowers are ample reward for
the extra trouble needed to cultivate them. Tropical Terrestrials Several
terrestrial orchid genera originate from the northern tropical areas of Australia. The
plants grow rapidly through the hot, wet summer and rest during the slightly cooler
winter. The largest species in the Kew collection is Phaius
tankervilleae. Copious watering and foliar feeding at fortnightly intervals result in
its majestic leaves growing up to 100 cm. This species grows naturally along the margins
of swamps, with its roots in the water for part of the year, and has flower spikes up to 2
m tall. The flowers are white on the outside and gingery brown within except for the lip
which is usually pale on the outside and rose-pink within. This species flowered first in
England in Yorkshire in 1778, and was introduced to Kew in the same year by Sir Joseph
Banks, the President of the Royal Society at the time. Phaius australis var. bernaysii, which has yellow and white flowers, is
also grown at Kew. The related
genus Calanthe has 120 species worldwide, but
only the widespread Calanthe triplicata is found
in Australia. This species forms fine clumps of deep green, ribbed leaves about 60 cm tall
through which the spikes of delicate white flowers protrude. Malaxis latifolia has equally handsome foliage and
produces a raceme of tiny pale green flowers which turn purple after a few days. The compost
used for the tropical terrestrial orchids from Australia imitates the humus-rich layer
over the rain forest soils in which the wild plants grow. A mixture composed of leaf
mould, peat and loam, lightened with coarse sand, is used at Kew. Repotting is done
annually so that the roots never have to suffer stagnant compost. All these plants are
grown at Kew in a glasshouse in shady conditions with a winter night minimum temperature
of 14º C (61ºF). Epiphytes The
Australian epiphytes, of which there are over 200 species, grow most commonly in the
north-east of Australia and along the east coast, with only five species occurring as far
south as Victoria. They grow naturally on trees and rocks and have evolved root systems
which adhere strongly to the substratum. Those grown at Kew are mainly from the genera Cymbidium, Bulbophyllum, Dendrobium and Sarcochilus. The genus Cymbidium contains about 44 species worldwide.
There are three species in Australia, each of which has a different habitat. Cymbidium madidum grows readily in cultivation in
standard cymbidium compost, soon becoming a large plant in a 30 cm pot. It grows in nature
in moist open forest or rain forest and needs a winter night minimum temperature of 16ºC
(61ºF) in cultivation and quite shady conditions. Its stout leaves grow up to 35 cm long
and are a dark glossy green. The flowers grow on pendulous spikes and are fleshy and
long-lasting, varying in colour from yellowy brown to green. Cymbidium canaliculatum grows in the drier inland
woodland as well as coastal forests. It grows in the clefts of living or dead gum trees,
where its roots penetrate deeply into the heartwood finding both moisture and protection
from extremes of temperature. The leaves are few, thick, fleshy and gray-green, the
flowers variable, ranging from brown and red through purple to green. This species needs
the maximum available amount of light in cultivation and is hung close to the glass in the
warmest greenhouse with a winter night temperature of 17ºC (64ºF). Plants are grown in
hollow logs made of cork oak bark, which seem to suit them better than plastic pots. Cymbidium suave has soft, grass-like foliage and a
long slender stem. It is unusual in the genus in not forming pseudobulbs. The flowers are
greenish in colour and sweetly scented. Like C. canaliculatum,
C. suave is grown in hollow logs rather than pots but it is kept in a cooler
glasshouse. Twenty-seven
species of Bulbophyllum grow in Australia, 14 of
which are grown at Kew. All are grown on slabs of cork oak bark and are kept quite shaded
in a greenhouse with a winter night minimum temperature of 15ºC (60ºF). Over the years,
these plants form mats of small, green pseudobulbs joined by short rhizomes. In Australia,
bulbophyllums grow mainly in the rain forests close to the coast. Bulbophyllum baileys is the largest species with
solitary flowers up to 4 cm across, white or yellow with purple spots. The genus Dendrobium has over 70 species in Australia in a
wide range of habitats. More than half this total is cultivated at Kew in three different
glasshouses. Dendrobium bigibbum, the Cooktown
orchid, is the floral emblem of Queensland. Its pseudobulbs grow up to 45 cm tall with a
tuft of leaves at the top of each and arching sprays of mauve flowers in the autumn. The
variety D. bigibbum ssp. bigibbum var. superbum has larger flowers than normal while the
var. compactum has small flowers in cultivation.
Dendrobium discolor forms dense thickets of
enormous stems up to 3 m tall in the wild and is scarcely less vigorous in cultivation so
it needs a high greenhouse. Its glossy new growth is most attractive and its arching
racemes can be up to 30 cm long. The petals and sepals are brown and yellow and usually
twisting and curled, adding to the interest of the plant. Both these species grow well in
the brightly lit and warmest glasshouse at Kew. The
pendulous species, Dendrobium tetragonum and D. teretifolium, are grown in a shadier, cooler
greenhouse with a winter night minimum temperature of 17ºC (60ºF). They are mounted on
slabs of cork oak bark so that the flowers are presented in their natural posture. Dendrobium teretifolium, known sometimes as the
bridal veil orchid, cascades like a chandelier and is covered with small white flowers
each winter. Dendrobium tetragonum has
distinctive square pseudobulbs with a tuft of dark green leaves at the end of each one.
The flowers are yellow and brown or green and white and of spidery appearance. The tiny D. toressae grows under the same conditions. Its
leaves are similar in size and shape to grains of rice and its yellow flowers are just as
small. A cooler
glasshouse, with a winter night minimum temperature of 14ºC (57ºF), is used for growing
the very spectacular D. speciosum. This variable
species grows on rock outcrops in full sun and also on tree stumps in shade. Some clones
flower better than others in cultivation. The best are absolutely magnificent with long
spikes of densely packed, creamy-coloured flowers growing from each stubby pseudobulb. Dendrobium speciosum grows well in pots of medium
grade epiphyte compost. Dendrobium kingianum is another
lithophyte which grows on cliff faces where its roots become entangled in mats of moss and
ferns. Its flowers are usually pink, although a range from white through to mauve has been
found. Dendrobium speciosum . and D.
kingianum form a natural hybrid, Dendrobium X
delicatum, which has characteristics
intermediate between its parents. It grows vigorously in cultivation and has pink or white
flowers. Although rare in the wild, it is quite commonly cultivated, often erroneously
labelled D. kingianum 'album'. Seven
species of the genus Sarcochilus are grown at
Kew. They are all kept in a glasshouse with a winter night minimum temperature of 13ºC
(55º F) but the individual species differ in the amount of shade they prefer. Sarcochilus ceciliae is grown in an open position
in shallow pans of coarse compost where it forms compact tufts of foliage and dainty
racemes of pink flowers. It needs to be grown with the crown of each plant standing proud
of the surface of the compost so that it does not rot. Sarcochilus falcatus and S. olivaceus are both pendulous in habit and are grown
mounted on to slabs of cork oak bark. They form large root systems which are misted over
daily with water. Sarcochilus falcatus, the
orange blossom orchid, has pure white flowers with the lip of each striped with yellow and
orange, while S. olivaceus has olive-green
flowers with red markings. Sarcochilus hartmannii and
S. fitzgeraldii are erect in habit and make
compact plants. Both have white flowers with red markings at the bases of the petals. The
flowers of Sarcochilus fitzgeraldii have a
larger lip and the plants prefer a shaded position in the glasshouse. The natural habitat
of this species is the dark, mossy ravines of the Dividing Range in New South Wales. Sarcochilus hartmannii is found in sunnier
positions on rock faces and so does better in a more open position on the bench. Both
species grow well either mounted on cork oak bark or in pots of medium grade epiphyte
compost. Sarcochilus fitzgeraldii is now
endangered in the wild and plants at Kew are deliberately pollinated so that many more
seedlings can be raised and distributed around the world in the hope of reducing the need
to remove more wild plants from their natural habitat. The artificial hybrid between these
two species, Sarcochilus Fitzhart, grows
vigorously, and is more common in cultivation than either parent. Australia's most graceful orchid, Phalaenopsis amabilis var. papuana occurs sporadically along the Mossman and Daintree Rivers in dense forest. Each plant has several pendulous leaves and is secured to the host tree by its long flat roots. Five to ten glistening white flowers are borne on each arching inflorescence. This is the only species of Phalaenopsis which occurs in Australia. At Kew it is grown with other species of Phalaenopsis in a shady and very humid position in the warmest glasshouse with a winter night minimum temperature of 18ºC (64ºF). Its flowering period is one of the highlights of the year. |
