Editing Orchid (section)

== Description ==
[[File:Orchid high resolution.jpg|thumb|A ''Phalaenopsis'' flower]]

Orchids are easily distinguished from other plants, as they share some very evident derived characteristics or [[Synapomorphy|synapomorphies]]. Among these are: [[symmetry (biology)#Bilateral symmetry|bilateral symmetry]] of the flower ([[zygomorphic|zygomorphism]]), many [[resupination#Orchidaceae|resupinate]] flowers, a nearly always highly modified [[petal]] (labellum), fused [[stamen]]s and [[carpel]]s, and extremely small [[seed]]s.

=== Stem and roots ===
[[File:Anacamptis fragrans.JPG|thumb|Germinating seeds of the temperate orchid ''[[Anacamptis coriophora]]'']]
All orchids are [[perennial plant|perennial]] [[herbaceous plant|herb]]s that lack any permanent [[Lignin|woody]] structure. They can grow according to two patterns:
* '''[[Monopodial]]''': The stem grows from a single bud, leaves are added from the apex each year, and the stem grows longer accordingly. The stem of orchids with a monopodial growth can reach several metres in length, as in ''[[Vanda]]'' and ''[[Vanilla (genus)|Vanilla]]''.
* '''[[Sympodial]]''': Sympodial orchids have a front (the newest growth) and a back (the oldest growth).<ref>Nash, N., and Frownie, S. (2008). ''Complete guide to orchids''. (Meredith Publishing Group) p. 12.</ref> The plant produces a series of adjacent shoots, which grow to a certain size, bloom and then stop growing and are replaced. Sympodial orchids grow horizontally, rather than vertically, following the surface of their support. The growth continues by development of new leads, with their own leaves and roots, sprouting from or next to those of the previous year, as in ''[[Cattleya]]''. While a new lead is developing, the [[rhizome]] may start its growth again from a so-called 'eye', an undeveloped bud, thereby branching. Sympodial orchids may have visible [[pseudobulb]]s joined by a ''[[rhizome]]'', which creeps along the top or just beneath the soil.

[[File:Orchis lactea rhizotubers.jpg|thumb|right|''[[Neotinea lactea]]'',
collected in [[Sardinia]]; the small size, compared to a one-Euro coin, and the two [[Globose (botany)|globose]] tuberoids typical of the ''[[Neotinea]]'' genus are highlighted]]

Terrestrial orchids may be [[rhizome|rhizomatous]] or form [[corm]]s or [[tuber]]s. The root caps of terrestrial orchids are smooth and white.

Some sympodial terrestrial orchids, such as ''[[Orchis]]'' and ''[[Ophrys]]'', have two subterranean [[tuberous root]]s. One is used as a food reserve for wintry periods, and provides for the development of the other one, from which visible growth develops.

In warm and constantly humid climates, many terrestrial orchids do not need pseudobulbs.

[[Epiphyte|Epiphytic]] orchids, those that grow upon a support, have modified [[aerial root]]s that can sometimes be a few meters long. In the older parts of the roots, a modified spongy [[epidermis (botany)|epidermis]], called a [[velamen]], has the function of absorbing humidity. It is made of dead cells and can have a silvery-grey, white or brown appearance. In some orchids, the velamen includes spongy and fibrous bodies near the passage cells, called tilosomes.

The cells of the root epidermis grow at a right angle to the axis of the root to allow them to get a firm grasp on their support. Nutrients for epiphytic orchids mainly come from mineral dust, organic detritus, animal droppings and other substances collecting among on their supporting surfaces.

[[File:Pseudobulbe.jpg|thumb|Pseudobulb of ''[[Prosthechea fragrans]]'']]
The base of the stem of sympodial epiphytes, or in some species essentially the entire stem, may be thickened to form a [[pseudobulb]] that contains nutrients and water for drier periods.

The pseudobulb typically has a smooth surface with lengthwise grooves, and can have different shapes, often conical or oblong. Its size is very variable; in some small species of ''[[Bulbophyllum]]'', it is no longer than two millimeters, while in the largest orchid in the world, ''[[Grammatophyllum speciosum]]'' (giant orchid), it can reach three meters. Some ''[[Dendrobium]]'' species have long, canelike pseudobulbs with short, rounded leaves over the whole length; some other orchids have hidden or extremely small pseudobulbs, completely included inside the leaves.

With ageing the pseudobulb sheds its leaves and becomes dormant. At this stage it is often called a backbulb. Backbulbs still hold nutrition for the plant, but then a pseudobulb usually takes over, exploiting the last reserves accumulated in the backbulb, which eventually dies off, too. A pseudobulb typically lives for about five years. Orchids without noticeable pseudobulbs are also said to have growths, an individual component of a sympodial plant.

=== Leaves ===

Like most [[monocot]]s, orchids generally have simple [[leaf|leaves]] with [[Leaf#Vein|parallel veins]], although some [[Vanilloideae]] have reticulate [[leaf|venation]]. Leaves may be ovate, lanceolate, or orbiculate, and very variable in size on the individual plant. Their characteristics are often diagnostic. They are normally [[phyllotaxis|alternate]] on the stem, often folded lengthwise along the centre ("plicate"), and have no [[stipule]]s. Orchid leaves often have [[silica|siliceous]] bodies called stegmata in the [[vascular bundle]] sheaths (not present in the [[Orchidoideae]]) and are fibrous.

The structure of the leaves corresponds to the specific habitat of the plant. Species that typically bask in sunlight, or grow on sites which can be occasionally very dry, have thick, leathery leaves and the [[Leaf anatomy|laminae]] are covered by a waxy [[Plant cuticle|cuticle]] to retain their necessary water supply. Shade-loving species, on the other hand, have long, thin leaves.

The leaves of most orchids are perennial, that is, they live for several years, while others, especially those with plicate leaves as in ''[[Catasetum]]'', shed them annually and develop new leaves together with new pseudobulbs.

The leaves of some orchids are considered ornamental. The leaves of ''[[Macodes sanderiana]]'', a semiterrestrial or rock-hugging ("[[lithophyte]]") orchid, show a sparkling silver and gold veining on a light green background. The cordate leaves of ''[[Psychopsiella|Psychopsiella limminghei]]'' are light brownish-green with maroon-puce markings, created by flower pigments. The attractive mottle of the leaves of [[lady's slipper]]s from tropical and subtropical Asia (''[[Paphiopedilum]]''), is caused by uneven distribution of chlorophyll. Also, ''[[Phalaenopsis schilleriana]]'' is a pastel pink orchid with leaves spotted dark green and light green. The jewel orchid (''[[Ludisia|Ludisia discolor]]'') is grown more for its colorful leaves than its white flowers.

Some orchids, such as ''[[Dendrophylax lindenii]]'' (ghost orchid), ''[[Aphyllorchis]]'' and ''[[Taeniophyllum]]'' depend on their green roots for [[photosynthesis]] and lack normally developed leaves, as do all of the [[heterotrophy|heterotrophic]] species.

Orchids of the genus ''[[Corallorhiza]]'' (coralroot orchids) lack leaves altogether and instead have symbiotic or parasitic associations with fungal mycelium, though which they absorb sugars.<ref>{{cite web |author=Jenny King |title=The coralroot orchid |url=http://www.exploresmos.org/nature/orchids-northern-washington-state/ |work=Orchids in Northern Washington State |publisher=Silvercrown Mountain Outdoor School |access-date=10 June 2011 |date=2011-06-10 |archive-date=21 October 2011 |archive-url=https://web.archive.org/web/20111021054855/http://www.exploresmos.org/nature/orchids-northern-washington-state/ |url-status=usurped }}</ref>

=== Flowers ===
Orchid flowers have three [[sepal]]s, three petals and a three-chambered [[Ovary (botany)|ovary]]. The three sepals and two of the petals are often similar to each other but one petal is usually highly modified, forming a "lip" or [[Labellum (botany)|labellum]]. In most orchid genera, as the flower develops, it undergoes a twisting through 180°, called [[resupination]], so that the labellum lies below the [[Column (botany)|column]]. The labellum functions to attract insects, and in resupinate flowers, also acts as a landing stage, or sometimes a trap.<ref name="Hoffman">{{cite book |last1=Hoffman |first1=Noel |last2=Brown |first2=Andrew |title=Orchids of South-West Australia. |date=August 2011 |publisher=Noel Hoffman |location=Gooseberry Hill |isbn=9780646562322 |page=13 |edition=3rd}}</ref><ref name="Brown">{{cite book |last1=Brown |first1=Andrew |last2=Dixon |first2=Kingsley |last3=French |first3=Christopher |last4=Brockman |first4=Gary |title=Field guide to the orchids of Western Australia : the definitive guide to the native orchids of Western Australia |date=2013 |publisher=Simon Nevill Publications |location=Floreat, W.A. |isbn=9780980348149 |pages=16–17}}</ref><ref name="nzpcn">{{cite web |title=Structure of orchid flowers |url=https://www.nzpcn.org.nz/flora/vascular/flowering-plants/monocots/orchids/structure/ |publisher=New Zealand Plant Conservation Network |access-date=15 April 2022}}</ref><ref name="boo">{{cite web |last1=Zimmermann |first1=Pedro |title=Anatomy of an Orchid |url=https://sites.millersville.edu/jasheeha/webDesign/websites/OOroot/anatomy.html |publisher=Brasilian Orchid Organisation |access-date=15 April 2022}}</ref>
[[File:Caladenia alpina (labelled).jpg|thumb|Labelled image of ''[[Caladenia alpina]]'']][[File:Diuris (labelled).jpg|thumb|Labelled image of ''[[Diuris carinata]]'']]

The reproductive parts of an orchid flower are unique in that the [[stamen]]s and [[Style (botany)|style]] are joined to form a single structure, the [[column (botany)|column]].<ref name="nzpcn" /><ref name="boo" /><ref>{{Cite web |url=http://www.botany.hawaii.edu/faculty/carr/orchid.htm |title=Flowering Plant Families |last=Carr |first=Gerald |date=30 October 2005 |website=Vascular Plant Family |publisher=University of Hawaii Botany Department |access-date=3 August 2022}}</ref> Instead of being released singly, thousands of [[pollen]] grains are contained in one or two bundles called [[Pollinium|pollinia]] that are attached to a sticky disc near the top of the column. Just below the pollinia is a second, larger sticky plate called the [[Stigma (botany)|stigma]].<ref name="Hoffman" /><ref name="Brown" /><ref name="nzpcn" /><ref name="boo" />