Herbs, either terrestrial and tuberous-rooted, with annual-herbaceous stems; or epiphytes with creeping rhizomes emitting, fibrous or fleshy roots and bearing simple or branched leafy stems often thickened into pseudobulbs. Flowers hermaphrodite, solitary or in spikes or racemes or panicles, often large and showy. Perianth superior, irregular, of 6 free or more or less combined segments, in 2 series; the 3 outer (sepals) all similar or the dorsal one larger and more concave than the 2 lateral which are always alike; the 3 inner (petals) always dissimilar (except in Thelymitra), the 2 lateral alike, but the third (called the lip, or labellum) usually exceedingly different, often spurred, lobed, fringed, or furnished with glands or other appendages. Stamens and style confluent into a fleshy variously shaped central body facing the lip, called the column; anther usually solitary (2 in Cypripedium),. placed on the front, top, or back of the column, and either free or adnate to it, persistent or deciduous, usually 2-celled; pollen granular or waxy, usually cohering in each cell into 1, 2, or 4 pairs of pollen-masses (pollinia), which are either free or attached, directly or by a caudicle, to a gland on the apex of the stigma (rostellum). Ovary inferior, 1-celled; ovules numerous, on 3 parietal placentas; stigma a viscid depression towards the top or on the front of the column, below the anther, facing the lip, upper margin often produced into a beak or point called the rostellum. Fruit a 1-celled 3-valved capsule; seeds numerous, very minute; testa loose, reticulate; albumen wanting; embryo solid, fleshy.

A very extensive and distinct family, found in almost all parts of the world,. but rare or absent in extreme northern or southern latitudes, and on the tops of high alpine mountains. Most of the species found in temperate countries are terrestrial; but in the tropics the greater number are epiphytes, growing upon the branches or trunks of trees or on rocks. The genera are estimated at 340, the species at 5000. Notwithstanding the great extent of the order, it is singularly deficient in useful plants. The only one possessing any commercial importance is vanilla, the scented pods of which are used for flavouring delicate dishes or liqueurs. The great beauty and singularity of the flowers of many of the tropical species have caused them to be extensively cultivated in hothouses, and probably over 2000 distinct species are now grown by European horticulturists.

The close affinity existing between the flora of New Zealand and that of Australia is nowhere better shown than in the Orchidece. Out of 21 genera found in New Zealand, 19 occur in Australia as well, and 8 are absolutely confined to the two countries, while several others have a very limited additional range. The only genera with a wide distribution are Dendrobium, Bulbophyllum, and Spiranthes. Earina, which does not occur in Australia, is found in the Pacific islands, while Townsonia is endemic.

A. Epiphytes with creeping rhizomes, perennial stems, and evergreen leaves. Pollinia waxy, free or attached by caudicles to the rostellum.
* Pollinia free.
The New Zealand species with slender much-branched stems, no pseudobulbs and axillary flowers. Lateral sepals and lip adnate to the base of the column	1. Dendrobium.page 661
The New Zealand species forming small matted patches on the trunks of trees, furnished with pseudobulbs. Flowers on a scape rising from the base of the pseudobulb. Lip jointed on to the base of the column, mobile	2. Bulbophyllum.
Stems leaf, unbranched. Flowers in terminal panicles. Lateral sepals free. Lip 3-lobed	3. Eaeina.
** Pollinia attached to the rostellum by a caudicle.
Stems short, leaves few. Flowers small, in lateral racemes. Lip 3-lobed	4. Sarcochilus.
B. Terrestrial, with tuberous roots and annual stems. Pollinia granular or powdery,
* Leaves long, very narrow-linear, flat or terete.
a. Leaves more than one.
Flowers numerous, on a spirally twisted spike. Dorsal sepal and petals connivent into a hood. Lip undivided	5. Spiranthes.
Flowers several, spicate. Dorsal sepal broad, hooded; lateral linear or filiform, erect. Lip 3-lobed	7. Orthoceras.
b. Leaf solitary.
Sepals, petals, and lip all similar in shape, petaloid. Colurnn very short, not attached to the lip at the base	6. Thelymitra.
Dorsal sepal concave. Petals much smaller. Surface of lip covered with long hairs. Column very short	14. Calochilus.
Dorsal sepal concave. Lip uppermost, undivided, usually with an adnate gland on the disc. Column very short, with two lateral erect appendages	9. Peasophyllum.
Dorsal sepal concave. Lip below, entire or 2-lobed. Column very short	8. Microtis.
Sepals and petals all linear. Lip uppermost, articulate, clawed; lamina peltate, irritable and mobile. Column long, winged	10. Caleana.
Sepals and petals narrow. Lip entire or 3-lobed, not jointed or irritable, disc with glandular processes, margin often fringed. Column long, winged above	16. Caladenia.
** Leaves shorter, two or several, oblong or lanceolate or linear.
Leaves numerous; radical broad, sometimes wanting; cauline narrow. Flowers hood-shaped, green. Lateral sepals united at the base. Lip narrow, irritable, with a basal appendage	11. Pterostylis,
Leaves 2–3, lanceolate. Upper sepal broad, concave; lateral narrow. Lip broad, papillose or ridged. Column not winged	15. Lyperanthus.
Leaves 2, radical, oblong. Upper sepal broad, concave; lateral narrow-linear. Lip broad, with raised glands on the disc. Column winged, wings produced into 2 erect lobes at the top	17. Chiloglottis.
*** Leaf solitary, broad.
Flower solitary, large, purple. Upper sepal broad, concave; lateral and petals long and filiform or minute. Lip large, broad, involute. Column very short	20. Corysanthes,page 662
Flower solitary. Upper sepal narrow, concave; lateral and petals lanceolate. Lip 3-lobed; disc with raised glands. Column long, winged above; wing produced upwards into 2 toothed lobes	18. Adenochilus.
Flowers 1 or 2. Upper sepal broad, concave; lateral lanceolate. Petals minute. Lip broad, undivided; disc smooth. Column long, equally winged, wings not produced upwards	19. Townsonia.
Flowers several. Sepals and petals narrow, acuminate. Lip spreading, broad, concave. Column long	12. Acianthus.
Flowers 2–3. Sepals and petals linear, obtuse. Lip spreading, narrow, flat. Column long, winged above	13. Cyrtostylis.
**** Leafless. Stem tall, with brown sheathing scales.
Sepals and petals united into a 5-lobed ventricose tube	21, Gastrodia.

The above clavis is purely artificial, and is solely intended to facilitate the determination of the genera. The following arrangement, which is adapted from Hooker and Bentham's "Genera Plantarum" and Engler's "Pflanzen-familien," is more natural and shows the sequence adopted in this work:—

Tribe I. EpidendReÆ.—Anther lid-like, usually deciduous; cells parallel, distinct, Pollinia waxy, 1–4 in each cell, free, or those of each cell connected by a viscid appendage, not attached by their bases or by a caudicle to the rostellum.

1. Dendbobium. 2. Bulbophyllum. 3. Earina.

Tribe II. VandeÆ.—Anther lid-like, usually deciduous, resting on the rostellum; cells usually confluent. Pollinia waxy, usually 2 or 4 in superposed pairs, attached singly or in pairs to a gland or process of the rostellum, which comes away with them when they are removed.

4. Sarcochilus.

Tribe III. NeottieÆ.—Anther lid-like or erect and persistent; cells distinct, parallel. Pollinia granular or powdery.

	Subtribe 1. Spirantheœ.
5. Spiranthes.
	Subtribe 2. Thelymitreœ.
6. Thelymitba.
	Subtribe 3. Diurideœ.
7. Orthocebas. 8. Microtis. 9. Pbasophyllum.
	Subtribe 4. Pterostylideœ.
10. Caleana. 11. Pterostylis.
	Subtribe 5. Caladeniœ.
12. Acianthus. 13. Cyrtostylis. 14. Calochilus. 15. Lyperanthus. 16. Caladenia. 17. Chiloglottis. 18. Adenochilus. 19. Townsonia.
	Subtribe 6. Pogonieœ.
20. Coeysanthes.
	Subtribe 7. Gastrodieœ.
21. Gastrodia.