Orchidaceae Juss.

Timothy Utteridge & Gemma Bramley (2020). The Kew Tropical Plant Families Identification Handbook, Second Edition. Kew Publishing Royal Botanic Gardens, Kew

Note

Herbs, often epiphytes or with pseudobulbs. Roots often with a velamen. Flowers zygomorphic, with sexual organs fused into a column; median petal (lip or labellum) modified; pollen usually in pollinia; ovary inferior; many microseeds per fruit.

Recognition

Characters of similar families: Zingiberaceae: plants aromatic, leaves with an open sheath and ligule, one fertile stamen and petaloid staminodia in flower, pollinia absent. Corsiaceae: flowers with 6 stamens. Iridaceae: flowers with 3 stamens, fused sexual organs lacking. Asparagaceae: flowers usually with 6 stamens, fused sexual organs and pollinia lacking. Hypoxidaceae: flowers with 6 stamens, actinomorphic.

Morphology General Habit

Herbs with protocorms (the structure formed after the germination of the seed and before the development of the seedling plant)

Vegetative Multiplication

The protocorm has no radicle and instead has mycotrophic tissue; terrestrial (often tuberous), lithophytic or epiphytic (>75% of species), often with pseudobulbs, or climbing

Morphology Roots

Roots often with a velamen (a persistent outer layer of dead cells)

Morphology General Hair

Hairs present or absent

Morphology Leaves

Leaves entire, spirally arranged, usually distichous, often with a basal sheath, rarely reduced to scales

Morphology Reproductive morphology Inflorescences

Inflorescences racemose or paniculate

Morphology Reproductive morphology Flowers

Flowers usually resupinate (twisted through 180°), zygomorphic; outer tepals 3, usually petaloid, inner tepals (petals) strongly differentiated into two lateral petals and a highly modified median petal (lip or labellum); sexual organs mutually adnate, forming a column; anthers 1, 2 or 3, pollen usually in pollinia (large waxy or granular masses), usually 2, 4 or 8; ovary inferior with more than 1,500 tenuinucellate ovules per carpel

Morphology Reproductive morphology Fruits

Fruit usually a capsule with 1–6 longitudinal zones of dehiscence

Morphology Reproductive morphology Seeds

Seeds very small (microseeds), lacking phytomelan.

Distribution

About 760 genera and c. 26,000 species. Cosmopolitan, but the majority of species are found in the tropics and subtropics.

Ecology

Ranging from sea level to almost 5,000 m. In nearly all environments, except open water and true desert. They are dominant in places, particularly in nutrient-deficient habitats.

Description Author

Paul Wilkin and André Schuiteman

Orchidaceae, V.S. Summerhayes. Flora of West Tropical Africa 3:1. 1968

Morphology General Habit

Perennial, terrestrial, epiphytic or saprophytic herbs with rhizomes or tuberous roots or rootstock; stem leafy or scapose, frequently thickened at the base into pseudobulbs and bearing aerial assimilating roots

Morphology Leaves

Leaves undivided, alternate and often distichous, rarely opposite, sometimes all reduced to scales, often fleshy, sheathing at the base

Morphology Reproductive morphology Flowers

Flowers bracteate, hermaphrodite or very rarely polygamous or monoecious, zygomorphic; inflorescence spicate, racemose or paniculate, or flowers solitary

Morphology Reproductive morphology Flowers Perianth

Perianth epigynous, composed of 6 petaloid segments (tepals) in 2 whorls, or the outer whorl calyx-like and the inner corolla-like, or the outer rarely corolla-like and the inner minute, free or variously connate in each whorl; outer segments (sepals) imbricate or subvalvate, the middle segments of each whorl generally different in size and colour from the lateral ones, especially the middle petal which is often extremely complicated in structure and is termed the lip or labellum; the basal part of the labellum, the hypochile, is often articulated to the base of the column or is much constricted, when it is termed the claw; the middle part, the mesochile and the apical part, the epichile, may be variously lobed and often bear outgrowths. On account of the twisting of the ovary through 180°, the labellum is often placed in an abaxial position; frequently the labellum or more rarely the odd sepal is prolonged into a sac or spur, sometimes very long

Morphology Reproductive morphology Flowers Androecium

Stamens 2 or 1; stamens and style united to form a special structure (column), the apex of which may be produced vertically into stelidia or laterally into wings, and the base of which may be produced downwards to form a foot; anther or anthers 2-locular, introrse, opening by a slit lengthwise; often operculate, i$e$ can be lifted like a little cap; pollen granular or generally agglutinated into mealy, waxy or bony masses (pollinia); at one end the pollinium may be extended into a sterile portion (caudicle); the pollinia may be free in the anther-loculi or more or less loosely united

Morphology Reproductive morphology Flowers Gynoecium

Ovules very numerous and minute Ovary inferior, 1-locular with 3 parietal placentas or very rarely 3-locular with axile placentas, usually produced at the apex to form the column; stigmas 3 fertile, or more frequently the lateral 2 fertile, the other sterile and transformed into a small outgrowth (rostellum) which lies between the anther and the stigmas; a portion of the rostellum is sometimes modified into a viscid disk or disks (viscidia) to which the pollinia are attached, often by a stalk or stipes

Morphology Reproductive morphology Fruits

Fruit usually a capsule, mostly opening laterally by 3 or 6 longitudinal slits

Morphology Reproductive morphology Seeds

Seeds very numerous, minute, often drawn out at each end, or rarely winged, without endosperm; embryo not differentiated

George R. Proctor (2012). Flora of the Cayman Isands (Second Edition). Royal Botanic Gardens, Kew

Morphology General Habit

Perennial herbs of diverse habit, terrestrial, lithophilic or epiphytic, with tuberous, fleshy or otherwise specialized, velamentous roots

Morphology General Shoots

Shoots monopodial or sympodial-Leaves convolute or conduplicate, simple, entire, thin and plicate to fleshy and often leathery, sometimes reduced to scales

Morphology Reproductive morphology Inflorescences

Inflorescences of solitary flowers, corymbs, spikes, racemes or panicles

Morphology Reproductive morphology Flowers

Flowers usually perfect, epigynous, zygomorphic, bracteate; perianth of 3 sepals, similar or nearly so, 3 petals, the lateral similar and the median third petal dissimilar, usually larger, sometimes spurred or otherwise modified, in the superior position but usually inferior by the resupination (twisting) of the pedicellate ovary

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens much reduced, usually 1, more or less united with the style and stigma to form a column (gynostemium); pollen aggregated in pollinia and often attached to caudicles, stipes and a viscidium to form a pollinarium

Morphology Reproductive morphology Flowers Gynoecium Stigma

Stigmas 3, one of which is sterile and forms a structure known as the rostellum, a barrier between the stigma and anther, a portion of which often serves as part of the pollinarium apparatus; the lateral lobes of the stigma are viscid and receptive, united or separated

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary usually 1-celled, ovules numerous on 3 parietal placenta

Morphology Reproductive morphology Fruits

Fruit a 3-valved capsule with numerous, dust-like seeds, or rarely a many-seeded indehiscent berry; seeds lack endosperm

Note

After seed germination, growth of the plant is depends on symbiotic mycorrhizal fungi.

Distribution

One of the largest families of flowering plants with about 800 genera and 20,000 species. A cosmopolitan family with greatest abundance and diversity in the moist and wet tropics.

Gemma Bramley, Anna Trias-Blasi & Richard Wilford (2023). The Kew Temperate Plant Families Identification Handbook. Kew Publishing Royal Botanic Gardens, Kew

Recognition

Characters of similar families: Zingiberaceae: plants aromatic, leaves with open sheaths and ligule, petaloid staminodes, no pollinia, seed with endosperm. Asparagaceae: flowers actinomorphic, 3 or more stamens, no pollinia, seed with endosperm. Araceae: inflorescence a spadix with a single, basal bract, no other bracts.

Morphology General Habit

Herbs, mycotrophic at least as seedlings (some species mycoheterotrophic as mature plants), initially forming a protocorm (a leafless and rootless body); terrestrial, lithophytic, or epiphytic; temperate species often geophytes

Morphology Roots

Roots usually with a velamen (outer zone of dead cells), often thick, little-branched and sparse

Morphology General Hair

Hairs present or absent

Morphology Leaves

Leaves entire, spirally arranged or distichous, often with basal sheath, sometimes reduced to scales

Morphology Reproductive morphology Inflorescences

Inflorescences racemose or sometimes paniculate, often with a single flower only

Morphology Reproductive morphology Flowers

Flowers usually resupinate (the labellum situated below the column), zygomorphic, minute to large; 6 tepals in 2 whorls, petaloid; outer tepals (sepals) 3; inner tepals 3, comprising 2 petals and a usually very different labellum (lip); tepals sometimes connate; lip or sepals sometimes spurred; sexual organs fused into a column; anthers 1, 2 or very rarely 3; pollen usually clumped into pollinia (2, 4, 6 or 8 small bodies), rarely gel-like or powdery; ovary inferior with numerous (often >1,500) tenuinucellate ovules per carpel

Morphology Reproductive morphology Fruits

Fruit usually a capsule splitting open along 1–6 zones of dehiscence, rarely an elongate berry

Morphology Reproductive morphology Seeds

Seeds minute (microseeds), consisting of an embryo surrounded by a testa, lacking endosperm and phytomelan.

Distribution

Approximately 750 genera, 25,000–30,000 species. Cosmopolitan but predominantly tropical and subtropical, with >75% of the species epiphytic.

Ecology

Usually indicative of oligotrophic and biodiverse habitats.

Note

Herbs, in temperate regions mainly geophytes. Flowers zygomorphic; one tepal, the labellum, is usually quite different from the other five; sexual organs fused into a column; pollen clumped into pollinia; dust-like seed.

Description Author

André Schuiteman

Orchidaceae, I. la Croix and P.J. Cribb. Flora Zambesiaca 11:1. 1995

Morphology General Habit

Growth either sympodial or less commonly monopodial Perennial, terrestrial, saprophytic or epiphytic herbs or rarely scrambling climbers, with rhizomes, root-stem tuberoids or rootstocks with mycorrhizal fungi in the roots and often elsewhere

Morphology Stem

Stems usually leafy, but leaves often reduced to bract-like scales, one or more internodes at the base often swollen to form a pseudobulb; aerial, assimilating adventitious roots, often bearing one or more layers of dead cells called a velamen, are borne in epiphytic species

Morphology Leaves

Leaves glabrous or occasionally hairy, entire except at the apex in some cases, alternate or occasionally opposite, often distichous, frequently fleshy and often terete or canaliculate, almost always with a basal sheath which frequently sheaths the stem, sometimes articulated at the base of the lamina and sometimes with a false petiole

Morphology Reproductive morphology Inflorescences

Inflorescences erect to pendent, spicate, racemose or paniculate, one to many-flowered, basal, lateral or terminal, the flowers rarely secund or distichously arranged

Morphology Reproductive morphology Flowers

Flowers small to large, often quite showy, hermaphrodite or rarely monoecious and polymorphic, sessile or variously pedicellate, most often twisted through 180 degrees, occasionally not twisted or twisted through 360 degrees

Morphology Reproductive morphology Flowers Perianth

Perianth epigynous, of two whorls of three segments; outer perianth whorl (sepals) usually free but sometimes variously adnate, the median (dorsal) often dissimilar to the laterals, the laterals sometimes adnate to the column foot to form a saccate, conical or spur-like mentum; inner whorl comprising two lateral petals and a median lip; petals free or rarely partly adnate to sepals, similar to sepals or not, often showy; lip entire, variously lobed or two or three-partite, ornamented or not with calli, ridges, hair cushions or crests, with or without a basal spur or nectary, margins entire to laciniate

Morphology Reproductive morphology Flowers Gynoecium

Stylar and filamentous tissue forming a long or short column, with or without a basal foot, occasionally winged or with lobes or arms at apex or ventrally; anther one (or rarely two or three in extra African taxa), terminal or ventral on column, with a concave anther cap or opening by longitudinal slits; pollen in tetrads, agglutinated into discrete masses called pollinia; pollinia mealy, waxy or horny, sectile or not, 2, 4, 6 or 8, sessile or attached by caudicles, a stipes or stipites to one or two sticky viscidia; stigma 3-lobed, the mid-lobe often modified to form a rostellum, the other lobes either sunken on the ventral surface of the column behind the anther or with two lobes porrect Ovary inferior, unilocular and the placentation parietal, or rarely trilocular and the placentation axile

Morphology Reproductive morphology Fruits

Fruit a capsule, opening laterally by 3 or 6 slits; seeds numerous, dust-like, lacking endosperm, sometimes markedly winged