Orchidaceae (the Orchids)

Abstract

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Keywords: Orchidaceae

Introduction

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Morphology

Phylogeny and Evolution

Affinities

Fossil Record

Origins

Evolution

Extinction

Systematics

Kingdom Plantae

Division Magnoliophyta

The angiosperms, characterised by a carpel enclosing the ovules. The carpel bears a receptive stigmatic surface for the (chemical) recognition of pollen.

Class Liliopsida

The monocotyledons, comprising approximately 30% of angiosperm species. Characteristics features include a single cotyledon (or leaf seed) in the embryo, leaves mainly with parallel longitudinal veins, and mostly trimerous floral organs (occurring in threes).

Subclass Liliidae

Order Orchidales

The orchids are perennial herbs with rhizomes or tuberous roots or root-stock, having bilaterally symmetrical (zygomorphic), mostly bisexual flowers. The "floral envelope" (perianth) is arranged in two whorls (biseriate), the outer whorl comprising three sepals and the inner whorl three petals. All six segments petaloid or outer three more sepaloid; middle segment in each whorl usually different from other two. Stamens one or two; pollen granular or fused into messes. Ovary inferior, usually 1-locular (having only one compartment) with very numerous ovules; often twisted through 180o to bring the middle petal (labellum) into abaxial position (facing away from the main stem); stigmas borne, with anthers, on a special structure (the column). Seed minute, without endosperm or differentiated embryo. Leaves undivided, often fleshy. (After Moore & Edgar 1976.)

Family Orchidaceae

Perennial, terrestrial, epiphytic or saprophytic herbs with rhizomes, tubes, of thickened rootstocks. Aerial stem often swollen at the base into pseudobulb, and often with adventitious or aerial roots.

Leaves usually entire (having a continuous smooth margin, lacking serrations), often distichous (arranged in two opposite rows so as to lie in one plane, e.g. Vanda spp.), sheathing at base, sometimes reduced to scales.

Flowers bisexual, zygomorphic, in spikes, inflorescences, or panicles, or solitary. Perianth mostly petaloid, of six segments in two whorls, free or variously connate, occasionally joined to form a tube; the middle segment in each whorl usually different from the two lateral ones, the middle petal or labellum often differing greatly in size, shape or outgrowths (calli) from the others and usually directed downwards; nectary sometimes contained within a spur or sac from one or more of the perianth segments (easily seen in Masdevallia infracta, described below).

Anthers and stigmas borne on a more or less erect, usually fleshy structure, the column. Anthers one or two, 2-locular (having two compartments), introrse (opening towards the centre of the flower), opening by longitudinal slits; pollen grains rarely free, usually aggregated in tetrads or larger groups (pollinia) that are mealy, waxy, or quite hard and sometimes terminate in a sterile caudicle (a small tail-like appendage).

Ovary inferior (below the junction of sepals and petals), 1-locular with three parietal placentae (ovules are borne on three placentae which occur on the walls of the ovary) (rarely 3-locular); stigma borne on the part of the column facing the labellum, of three or two lobes, the median lobe sometimes represented by a small process, the rostellum, between the stigma and the anther; viscid areas (viscidia) are sometimes associated with the rostellum and to these the pollinia become attached either directly or by a connecting strip of non-viscid rostellar or columnar tissue known as the stipe.

Fruit usually a capsule dehiscing (shedding seeds) through three or six longitudinal slits. Seeds very numerous, minute, often elongated, without endosperm or differentiated embryo. (After Moore & Edgar 1976.)

[Rank] [Taxon] [Authority]

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Type: [Taxon] [Authority]

Original Diagnosis: xxx

Description: xxx

Habit: xxx

Distribution Occurrence: xxx

Discussion: xxx

Conservation

Hybrids

Beginning a Collection

Culture

Temperature/Potting/Substrate/Watering/Feeding/Humidity

Hygiene

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Conclusion

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Further Information

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References

Cameron, Kenneth M.; Chase, Mark W.; Whitten, W. Mark; Kores, Paul J.; Jarrell, David C.; Albert, Victor A.; Yukawa, Tomohisa; Hills, Harold G.; Goldman, Douglas H. 1999: A Phylogenetic Analysis of the Orchidaceae: Evidence From rbcL Nucleotide Sequences. American Journal of Botany 86 (2): 208-224.