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Family Orchidaceae

Synonyms: Apostasiaceae APNI*

Description: Perennial, terrestrial, epiphytic, epilithic or climbing herbs, occasionally saprophytic; often with rhizome, tuber, fleshy roots, root-stem tuberoids or rootstock; stems leafy or scapose, sometimes thickened into pseudobulbs and/or bearing aerial roots; roots often covered with a spongy layer of dead cells (velamen).

Leaves simple, usually alternate, often distichous, rarely opposite, well-developed and green or sometimes all reduced to scales, often fleshy, usually sheathing at base, sheath usually closed and encircling stem, usually not petiolate.

Inflorescences terminal or lateral; spicate, racemose or paniculate or flowers solitary; flowers bracteate and often resupinate (with the ovary twisted to present the median petal lowermost in the flower). Flowers zygomorphic, bisexual or rarely unisexual and then plants polygamous or monoecious. Perianth of 6 ± petaloid segments in 2 whorls or the outer whorl sepaloid, free or variously fused in each whorl; outer segments ('sepals') often ± similar, imbricate or ± valvate; inner segments ('petals') usually unequal with laterals similar to each other and often to the sepals with middle petal (lower petal if flower resupinate) modified in structure and called the labellum. Stamens 1 [or 2], usually fused partly or completely to the 2 lateral staminodes and the style to form the 'column'; anthers 2-locular, introrse, dehiscing by longitudinal slits; pollen granular or agglutinated into mealy, waxy or bony pollinia; pollinium sometimes extended intoa sterile stalk (caudicle), pollinia free or loosely united. Ovary inferior, 1-locular with 3 parietal placentas [or rarely 3-locular with axile placentas]; stigma 3-lobed, part of the median lobe forming a sterile outgrowth (rostellum). Part of rostellum sometimes modified into viscid disc (viscidium) to which pollinia are attached; ovules numerous.

Fruit usually a capsule, mostly opening laterally by 3 or 6 longitudinal slits or rarely indehiscent; seeds numerous, minute, usually dust-like, without endosperm.

Distribution and occurrence: World: 850 genera, c. 25 000 species, cosmopolitan, especially Indo-Malaya & tropical America. Australia: c. 110 genera, c. 700 species, all States.

External links:
Angiosperm Phylogeny Website (Family: Orchidaceae, Order: Asparagales)

Orchids are important horticulturally. Many species and cultivars are widely grown for their bizarre beauty and for the cut-flower industry. Numerous nurseries specialize in the production of species, either by meristem culture or raising plants from seed, or specialize in producing artificial hybrids in order to achieve 'improvements' in flower size, shape and colour and the presentation of the flowers on the raceme. Many orchid species are potentially infertile as shown by the number of natural hybrids and the range of hybrids produced artificially. The hybrids are generally intermediate between the parents. Intergeneric hybrids are known to occur naturally between Caladenia and Glossodia.

Text by P. H. Weston and contributors as listed under genus headings
Taxon concept:

Column and pollinia in Orchidaceae. A & B column; A, side view; B, front view; CF, pollinia; C, Prasophyllum; D, Cryptostylis; E, Dipodium; F, Dendrobium.

Flower parts in Orchidaceae. A & B, diagramatic flower; A, side view; B, front view; CH, flowers resupinate; C, Dendrobium (front view); D, Dendrobium (side view); E, Sarcochilus; F, Thelymitra; G, Diuris; H, Caladenia; I, flower not resupinate, Prasophyllum. Abbreviations for flower parts: dorsal sepal (DS), lateral petals (LP), column (C), labellum (L), lateral sepals (LS).

Taxa not yet included in identification key
Danhatchia,    Epidendrum

 Key to the genera 
1Anther easily removed, cap-like, incumbent, bent downwards through 90–120° (except in Oberonia); plants mostly epiphytes or epiliths, or less commonly climbers or terrestrial herbs; tuberoids absent although roots or rhizomes fleshy in some terrestrial taxa; pseudobulbs often present; inflorescences lateral or terminal2
Anther persistent, not cap-like, erect, parallel to the axis of the column or bent downwards through less than 90° ; plants growing in soil or very rarely humus-epiphytes or humus-epiliths; tuberoids often present; pseudobulbs absent; inflorescences terminal24
2Climbing plants with stems arising from the ground; seeds winged3
Plants not climbing (sometimes creeping epiphytes appear to be climbing); seeds not winged
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3Leaves ovate, 3–6 cm long; labellum with numerous transverse, parallel ridges on both sides of median ridge, not warty; column with a short, descending foot, tapering into the median ridge of the labellumErythrorchis
Leaves triangular, less than 2.5 cm long; labellum without ridges but with most of its surface densely warty; column footless
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4Plants with leaves reduced to scales5
Plants with well-developed green leaves
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5Plants epiphytic or epilithic; roots creeping over surface of host; flowers less than 5 mm long6
Plants terrestrial; roots subterranean; flowers more than 5 mm long
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6Stems creeping, consisting of globose pseudobulbs, connected by filiform rhizomesBulbophyllum
Stems almost vestigial, not creeping, not differentiated into pseudobulbs and rhizomes
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7Sepals and lateral petals fused into a tube; flowers not resupinate, the labellum being the uppermost perianth segmentGastrodia
Sepals and lateral petals free; flowers resupinate
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8Labellum with a prominent basal spur, free, glabrousEpipogium
Labellum without a spur, fused to the base of the column, hairy on the upper surface
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9Leaves pleated, thin; plant growing in soil10
Leaves conduplicate or laterally flattened, thin to leathery or succulent; plant epiphytic, epilithic or rarely growing in soil
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10Dorsal sepal 3–6 cm long; sepals and lateral petals white on the outside, brown on the insidePhaius
Dorsal sepal 0.5–1.9 cm long; sepals and lateral petals not as above
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11Labellum with a hollow spur protruding backwards, with a deeply 4-lobed laminaCalanthe
Labellum lacking a hollow spur, with unlobed or obscurely 3-lobed or deeply 2-lobed lamina
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12Inflorescence axis erect basally but abruptly curved over towards the tip at flowering time, terete; flowers pink; labellum shallowly saccateGeodorum
Inflorescence axis completely erect, square in cross-section; flowers yellow-green to reddish purple; labellum not saccate
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13Fleshy stems held above ground; lateral sepals freeDiteilis
Fleshy stems subterranean; lateral sepals partly connate along adjacent margins
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14Sepals and petals less than 1 mm long; leaves laterally flattened; flowers arranged in loose whorls in the inflorescenceOberonia
Sepals and petals more than 1 mm long; leaves dorsiventrally flattened to terete; flowers not whorled
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15Labellum not saccate, lacking a hollow spur, attached to the base of the footless column16
Labellum saccate and/or possessing a hollow spur and/or attached to the tip of a prominent column foot
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16Inflorescences lateral; sepals 4–10 mm wideCymbidium
Inflorescences terminal; sepals 1–3 mm wide
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17Growth sympodial; stems often swollen to form pseudobulbs; lateral sepals basally fused to the prominent column foot to form a mentum18
Growth monopodial; stems never swollen; lateral sepals free; column foot present or absent
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18Stems either not differentiated into rhizome and pseudobulb, or if so differentiated then pseudobulb composed of more than just the most apical internode; each stem with 1–6 leaves at its apexDendrobium
Stems differentiated into rhizome and pseudobulb; pseudobulb composed of only the most apical internode; each pseudobulb with 1 leaf at apex
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19Roots strongly tuberculate, rough; sepals and lateral petals more than 10 times longer than broad, filiform; flowers lasting less than 2 daysRhinerrhiza
Roots smooth; sepals and lateral petals less than 10 times longer than broad, not filiform; flowers lasting more than 2 days
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20Labellum shallowly saccate, and sometimes with a solid, forward-pointing spur21
Labellum with a prominent, hollow, backward-pointing spur
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21Labellum with a hollow pouch at its front; inflorescence 1–25-floweredSarcochilus
Labellum with a hollow pouch at its rear; inflorescence 25–75-flowered
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22Labellum spur lacking calli; labellum midlobe papillosePapillilabium
Labellum spur with calli arising inside or overhanging its mouth; labellum midlobe not papillose
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23Labellum spur without internal calli but thickened base of midlobe extended part way across the orifice of the spur in the form of a broad, 2-fid callusSchistotylus
Labellum spur with a finger-like callus arising from the upper anterior wall and directed towards its apex
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24Inflorescence a dense capitulum with only the flowers and involucral bracts emerging above the soil surface, the peduncle and the rest of the plant entirely subterraneanRhizanthella
Inflorescence racemose or spicate or 1-flowered, mostly or wholly above the soil surface
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25Flowers not resupinate, the labellum positioned above the column26
Flowers resupinate, the labellum positioned below the column
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26Column almost as long as dorsal sepal27
Column much shorter than dorsal sepal
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27Column wings discontinuous, 4-lobed; labellum passively motile on basal hinge; leaves absent or 2—6 on a lateral shootArthrochilus
Column wings continuous, the whole column deeply concave; labellum actively motile, elastic, irritable, upcurved when set, recurved when sprung; leaf solitary, basal
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28Surface of labellum lamina smooth; column foot absentCaleana
Surface of labellum lamina warty; column foot present, separating the points of insertion of the labellum and lateral sepals from those of the dorsal sepal and lateral petals
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29Leaves narrow-elliptic to narrow-ovate, lamina flat, petiolate, connected to rhizome separately from the inflorescence or absent; labellum several times broader than sepals and lateral petals; plant lacking tuberoids, with fleshy rootsCryptostylis
Leaf linear, terete, tubular, enclosing inflorescence basally or rarely absent; labellum 1–2 times as broad as sepals and lateral petals; plant with paired tuberoids
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30Labellum articulate on a conspicuous claw, mobile; free apical part of leaf flattenedGenoplesium
Labellum sessile at the base of the column, immobile; free apical part of leaf terete
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31Stem differentiated into the erect, flowering shoot and succulent, creeping rhizome which is either rootless or which bears wiry roots at its nodes; tuberoids absent; stigma in 2 lateral parts, at the base of the deeply cleft rostellum32
Stem not differentiated into erect and creeping parts (except in Adenochilus), not succulent; plants with tuberoids or less frequently with fleshy roots or lacking fleshy subterranean structures; stigma entire
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32Petals fused to dorsal sepal, forming a hood over the column; lateral sepals free; roots present; rhizome not constrictedZeuxine
Petals free; sepals fused for about half their length to form a tube; roots absent; rhizome conspicuously constricted at the nodes
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33Lateral petals linear, 5–10 times narrower than lateral sepals; stigma sunk in a deep cavity that is partially covered by 2 flaps of the anther lid and a fleshy flap that is the lower margin of the stigmaEriochilus
Lateral petals slightly broader to slightly narrower than lateral sepals; stigma not as above
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34Flowering shoot leafless, but may have short acute leaf-like bracts35
Flowering shoot with 1 or more prominently developed leaves
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35Dorsal sepal and lateral petals adherent, forming a hoodPterostylis
Dorsal sepal and lateral petals free
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36Labellum densely covered by a beard of long, hair-like calli; column about a fifth as long as labellumCalochilus
Labellum with knob-like calli; column about half as long as labellum
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37Flowering shoot with a single, well-developed leaf that is much larger than the other, scale-like, foliar organs38
Flowering shoot with 2 or more well-developed leaves of similar size
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38Leaf cordate, heart-shaped or reniform, held horizontally39
Leaf not cordate, ovate to linear
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39Inflorescence consisting of a solitary, sessile flower; flower dominated by the labellum and hood-like dorsal sepal; lateral petals and sepals minuteCorybas
Inflorescence pedunculate, 1–many-flowered
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40Leaf basal, ground-hugging41
Leaf cauline, held horizontally above ground level
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41Labellum unlobed, almost flat, pinkish brown; plant not turning black on dryingCyrtostylis
Labellum shallowly 3-lobed, the lateral lobes erect, white with prominent red stripes; plant turning black on drying
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42Flower predominantly white; labellum 3-lobed, with a dense, central band of numerous, yellow, clubbed calli; plant rhizomatous, lacking tubersAdenochilus
Flower predominantly green to brown or purplish; labellum unlobed (but sometimes coarsely toothed), with a central plate-like or channelled callus and sometimes with 2 basal, gland-like calli; plant tuberous
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43Leaf green on undersurface, often deeply lobed; labellum coarsely toothed, lacking distinct, basal, gland-like calliAcianthella
43Leaf with purple pigmentation on undersurface, entire; labellum entire, with two basal, gland-like calliAcianthus
44Leaf at least sparsely hairy45
Leaf glabrous
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45Labellum with only 1 or 2 basal calliGlossodia
Labellum with more than 2 calli
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46Tubers partially encased in a few-layered tunic; flowers predominantly white, pink, yellow, red, brown or greenCaladenia
Tubers entirely encased in a multilayered tunic; flowers predominantly blue
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47Labellum prominently 3-lobed, with 2 central rows of white or yellow calliCyanicula
Labellum scarcely 3-lobed, with 4–6 rows of calli that are blue on the midlobe but white more basally
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48Leaf linear, terete, tubular, enclosing inflorescence basally; dorsal sepal less than 3 mm long; flowers uniformly greenMicrotis
Leaf linear to ovate, flat or channelled; dorsal sepal more than 3 mm long; flowers variously coloured but rarely uniformly green
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49Column not hooded nor collared; labellum 3-lobed, concave50
Column hooded or collared (with a mitra); labellum not lobed, flat
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50Inflorescence 1-flowered; column wings prominent, extending beyond the anther; plant lacking tubersAdenochilus
Inflorescence usually 2–8-flowered; column wings reduced, not exceeding anther; plant tuberous
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51Labellum usually densely covered by a beard of long, hair-like calli, or very rarely lacking calli but then column with 2 basal, lateral, dark glands; base of column with prominent ridged collarCalochilus
Labellum lacking calli, similar to lateral petals; column lacking basal, lateral glands; top of column ornamented by prominent hood or collar
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52Lateral sepals much longer and narrower than dorsal sepal; leaves linear, basal53
Lateral sepals similar in length and breadth to dorsal sepal; leaves mostly not linear, basal or cauline
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53Lateral petals oblong and concealed under dorsal sepalOrthoceras
Lateral petals consisting of a prominent claw ending in a rounded to ovate lamina, exposed
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54Sepals and lateral petals usually bright pink or rarely white, 4–5 mm long; column about as long as labellum; inflorescence many-flowered with flowers arranged in a spiralSpiranthes
Sepals and lateral petals green or brown to reddish, sometimes striped with white, usually more than 5 mm long; column at least half as long as labellum; inflorescence 1–18-flowered, flowers not arranged in a conspicuous spiral
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55Dorsal sepal and lateral petals adherent, forming a hood; lateral sepals basally fused; labellum usually irritablePterostylis
Sepals and petals free; labellum not irritable
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56Inflorescence 6–18-flowered; leaves several, basal or cauline or both; labellum calli obscure or absentRimacola
Inflorescence 1-flowered; leaves 2, basal; labellum calli conspicuous
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