Dendrobium speciosum, commonly known as the rock orchid or cane orchid,[2]: 403 is a species of highly variable Australian
orchid. Its
varieties can be found in a range of
habitats as
epiphytes (on branches or trunks of trees) or
lithophytes. It has a continuous distribution along the east coast of Australia and in distinct populations along the
Tropic of Capricorn. As a lithophyte, it forms gigantic spreading colonies on rocks and cliff faces, often exposed to full sun, with its roots forming dense, matted beds across the rock that anchor the plant. It can be found at altitudes from sea level to 900 metres (3,000 ft).[3]
Description
Dendrobium speciosum is an epiphytic or lithophytic
herb with spreading roots and cylindrical or tapered
pseudobulbs 50–1,800 mm (2–70 in) long and 10–60 mm (0.4–2 in) wide. Each pseudobulb has up to seven, usually thick, leathery leaves originating from its top, the leaves 50–250 mm (2–10 in) long and 10–80 mm (0.4–3 in) wide. The leaves can remain on the plant for up to twelve years. The flowers vary in colour from white to bright yellows and there is considerable variation in the length of the flowering
raceme, the number of flowers on it and the size of the flowers. The length of the flowering stem ranges from 50–800 mm (2–30 in) long and the number of flowers from two to two hundred. The flowers are 12–70 mm (0.5–3 in) long and 20–80 mm (0.8–3 in) wide. The
dorsalsepal is longer than the
lateral sepals but narrower and the
petals are about the same length as the lateral sepals but only half as wide. The
labellum has reddish purple spots or streaks and three lobes, the sides lobes erect and curved and the middle lobe pointed, rounded or more or less square. Flowering occurs between August and October for most varieties but some flower as early as May and others as late as November.[2][4]
Dendrobium speciosum var. blackdownenseP.B.Adams[8] which is usually a lithophyte, with between 14 and 113 off-white to deep golden yellow flowers from August to November and occurring on the
Blackdown Tableland;[4]
Dendrobium speciosum var. borealeP.B.Adams,
Jac.M.Burke &
S.D.Lawson[9] which is epiphytic or lithophytic, with between 9 and 125, star-like, widely opening, off-white to cream-coloured flowers from July to September and has the most northerly distribution of the species, from the
Annan River to near
Townsville;[4]
Dendrobium speciosum var. capricornicumClemesha[10] – commonly known as the Capricorn rock orchid, which is usually a lithophyte with between 30 and 50 white flowers between May and August and is found between the
Byfield Range,
Yeppoon and
Rockhampton;[2]: 409–410
Dendrobium speciosum var. carnarvonenseP.B.Adams[4][11] – commonly known as the gorge pink rock orchid, which grows in gorges near streams and has between 2 and 7 relatively small, pale pink flowers between August and November and is only found between
Carnarvon Gorge and
Isla Gorge;[2]: 408
Dendrobium speciosum var. curvicauleF.M.Bailey[12] – commonly known as the rainforest rock orchid, which is an epiphyte or lithophyte growing in or near rainforest and has between 25 and 45 white or cream-coloured flowers from July to September and grows between
Mossman and
Paluma in Queensland;[2]: 410
Dendrobium speciosum var. grandiflorumF.M.Bailey[13] – commonly known as the golden king orchid and which grows on trees or rocks and has between 50 and 150 relatively large, creamy yellow to bright yellow flowers from August to October and is found from the
Calliope Range to the
Bunya Mountains in Queensland;[2]: 411
Dendrobium speciosum var. hilliiMast.[14][15] – commonly known as the pale king orchid and which grows on trees and rocks and has between 70 and 200 crowde white or cream-coloured flowers from August to October and grows between
Maleny in Queensland to
Mangrove Mountain in New South Wales;[2]: 412
Dendrobium speciosum var. pedunculatumClemesha[16] – commonly known as the dwarf rock orchid which grows on rocks and has between 10 and 30 crowded white or cream-coloured flowers from July to August and occurs between the
Mount Windsor National Park and the
Evelyn Tableland in Queensland;[2]: 411
Dendrobium speciosumSm. var. speciosum[17] – commonly known as the Sydney rock orchid or rock lily which is a lithophyte with between 30 and 100 crowded cream-coloured or dull yellow flowers between August and October and occurs between
Bulahdelah and near the
Victorian border and as far inland as
Mudgee.[2]: 409
The 1889 book The Useful Native Plants of Australia records that common names included "rock lily" and that "the large pseudo-bulbs have been eaten by the aborigines, they, however, contain but little nutritive matter."[25]
Pollination
Potential pollinators of Dendrobium speciosum, such as the stingless bee Tetragonula carbonaria, are attracted to the plant by large, cream to yellow, finely segmented, aromatic inflorescences. Flowers vary in size within the six recognised varieties of D. speciosum and are pollinated when visited by bees of appropriate size.[26]
Natural hybrids
Dendrobium speciosum forms a natural hybrid with Dendrobium gracilicaule : Dendrobium × gracillimum. This hybrid has also been described as Dendrobium speciosum var. nitidum F.M.Bailey, Dendrobium × nitidum (F.M.Bailey) M.A.Clem. & D.L.Jones, Dendrobium speciosum var. bancroftianumRchb.f. and Dendrobium jonesiiRendle subsp. bancroftianum(Rchb.f.) M.A.Clem. & D.L.Jones.
Use in horticulture
This orchid is popular in cultivation, growing into a large specimen that does well outdoors in climates with a mild winter. It may be grown in an open, coarse orchid growing medium, on a sturdy tree with an open canopy, or as a terrestrial in a well-drained position. It requires very bright light to full sun. Watering is year round in moderation. It is very temperature tolerant as long as it receives good warmth during the growing season. Frost, however, can cause extensive defoliation, an event the plant may require years to recover from. In cultivation D. speciosum can develop extremely large pseudobulbs, and benefits from regular fertilisation.[3] Even in ideal cultivation conditions it may not flower every year, especially so in plants from more southern populations.
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abcdefghiJones, David L. (2006). A complete guide to native orchids of Australia including the island territories. Frenchs Forest, N.S.W.: New Holland.
ISBN1877069124.