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Merosity (from the greek "méros," which means "having parts") refers to the number of component parts in a distinct whorl of a plant structure. It is most commonly used in the context of flowers where it refers to the number of
sepal A sepal ( or ) is a part of the flower A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other p ...
s in a whorl of the calyx, the number of
petal Petals are modified leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together fo ...

petal
s in a whorl of the corolla, the number of
stamen The stamen (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ve ...
s in a whorl of the
androecium The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament and ...

androecium
, or the number of carpels in a whorl of the
gynoecium Gynoecium (; ) is most commonly used as a collective term for the parts of a flower A flower, sometimes known as a bloom or blossom Image:Cerisier du Japon Prunus serrulata.jpg, Cherry blossoms in Paris in full bloom. In botany, blossoms ...

gynoecium
. The term may also be used to refer to the number of leaves in a
leaf A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

leaf
whorl. The adjective ''n''-merous refers to a whorl of ''n'' parts, where ''n'' is any integer greater than one. In nature, five or three parts per whorl have the highest frequency of occurrence, but four or two parts per whorl are not uncommon. Be aware that two consecutive whorls of dimerous petals are often mistaken for tetramerous petals. If all of the whorls in a given floral arrangement have the same merosity, the flower is said to be isomerous, otherwise the flower is anisomerous. For example, ''
Trillium ''Trillium'' (trillium, wakerobin, tri flower, birthroot, birthwort, and sometimes "wood lily") is a genus of about fifty flowering plant species in the family Melanthiaceae. ''Trillium'' species are native to temperate regions of North America ...

Trillium
'' is isomerous since all whorls are trimerous (one whorl of three sepals, zero or one whorl of three petals, two whorls of three stamens each, and one whorl of three carpels). ''Trillium'' also has one whorl of three leaves.


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See also

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Cyclic flower A cyclic flower is a flower type formed out of a series of whorls A whorl is a type of spiral or circular pattern. Other meanings of whorl include: * Whorl (botany), the attachment of sepals, petals, leaves, or branches at a single point * Whorl ...
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Floral diagram Floral diagram is a graphic representation of flower A flower, sometimes known as a bloom or blossom, is the reproduction, reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angiosperms). T ...
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Floral formula Floral formula is a means to represent the structure of a flower A flower, sometimes known as a bloom or blossom, is the reproduction, reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angi ...


References

{{Reflist, refs= {{cite journal , last1=Ronse Decraene , first1=L. P. , last2=Smets , first2=E. F. , year=1994 , title=Merosity in flowers: definition, origin, and taxonomic significance , journal=Plant Systematics and Evolution , volume=191 , issue=1–2 , pages=83–104 , doi=10.1007/BF00985344 , url=https://www.academia.edu/25486804/Merosity_in_flowers_Definition_origin_and_taxonomic_significance , access-date=22 November 2019 {{cite web , last1=Eckel , first1=P. M. , title=A Grammatical Dictionary of Botanical Latin , url=http://www.mobot.org/mobot/latindict/keyDetail.aspx?keyWord=merus , access-date=22 November 2019
Plant morphology ''Plant morphology'' is the field in botany that studies the diversity in forms, with the naked eye or slight optical magnification. This is opposed to plant anatomy (see :Plant anatomy) that needs to cut into plants to be able to study its subject, ...