Editing Petal (section)

== Variations ==
[[File:Pelargonium peltatum 9245s.jpg|thumb|''[[Pelargonium peltatum]]'' flowers resemble those of [[geranium]]s, but are conspicuously [[zygomorphic]].]]
[[File:Geranium incanum 9156s.jpg|thumb|''Geranium incanum'', with an actinomorphic flower typical of the genus]] [[File:White pea flower.jpg|thumb|The white flower of ''[[Pisum sativum]]'', the Garden Pea: an example of a zygomorphic flower.]]
[[File:20140226Narcissus2.jpg|thumb|''[[Narcissus pseudonarcissus]]'' showing (from bend to tip of flower) [[spathe]], [[floral cup]], tepals, and [[perianth#corona|corona]]]]
[[File:使君子Combretum indicum 20210523080843 01.jpg|thumb|The petals of ''[[Combretum indicum]]'']]

Petals can differ dramatically in different species.  The [[merosity|number of petals in a flower]] may hold clues to a plant's classification.  For example, flowers on [[eudicots]] (the largest group of [[dicots]]) most frequently have four or five petals while flowers on [[monocotyledon|monocots]] have three or six petals, although there are many exceptions to this rule.<ref>{{cite journal |title= The origin and diversification of angiosperms |author= Soltis, Pamela S.|author-link = Pamela S. Soltis|author2 = Douglas E. Soltis |journal= American Journal of Botany |year= 2004 |volume= 91 | pages= 1614–1626 | doi= 10.3732/ajb.91.10.1614 |issue=10 |pmid=21652312|doi-access= free |bibcode= 2004AmJB...91.1614S}}</ref>

The petal whorl or corolla may be either radially or bilaterally [[Floral symmetry|symmetrical]]. If all of the petals are essentially identical in size and shape, the flower is said to be '''regular'''<ref name=EB1911/> or '''actinomorphic''' (meaning "ray-formed"). Many flowers are symmetrical in only one plane (i.e., symmetry is bilateral) and are termed '''irregular''' or '''zygomorphic''' (meaning "yoke-" or "pair-formed"). In ''irregular'' flowers, other floral parts may be modified from the ''regular'' form, but the petals show the greatest deviation from radial symmetry. Examples of zygomorphic flowers may be seen in [[orchid]]s and members of the [[pea family]].

In many plants of the [[aster family]] such as the sunflower, ''[[Helianthus annuus]]'', the circumference of the [[flower head]] is composed of [[ray floret]]s.  Each ray floret is anatomically an individual flower with a single large petal.  Florets in the centre of the disc typically have no or very reduced petals. In some plants such as ''[[Narcissus (plant)|Narcissus]]'', the lower part of the petals or tepals are fused to form a floral cup ('''[[hypanthium]]''') above the ovary, and from which the petals proper extend.{{sfn|Simpson|2011|loc=p. 365}}{{sfn|Foster|2014|loc=[http://plant-phytography.blogspot.ca/2012/10/hypanthium-cup-shaped-or-tubular.html Hypanthium]}}<ref name=Graham/>

A petal often consists of two parts: the upper broader part, similar to a leaf blade, also called the ''blade;'' and the lower narrower part, similar to a leaf [[Petiole (botany)|petiole]], called the ''claw'',<ref name=EB1911>{{Cite EB1911|wstitle=Flower|first=Alfred Barton|last=Rendle|volume=10|pages=561–563}}</ref> separated from each other at the ''limb''. Claws are distinctly developed in petals of some flowers of the family ''[[Brassicaceae]]'', such as ''[[Erysimum cheiri]]''.

The inception and further development of petals show a great variety of patterns.<ref>Sattler, R. 1973. ''Organogenesis of Flowers. A Photographic Text-Atlas''. University of Toronto Press.</ref> Petals of different species of plants vary greatly in colour or colour pattern, both in visible light and in ultraviolet. Such patterns often function as guides to pollinators and are variously known as [[nectar guide]]s, pollen guides, and floral guides.