Merosity (from the greek "méros," which means "having parts") refers to the number of component parts in a distinct
whorl of a plant structure.
The term is most commonly used in the context of a
flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...
where it refers to the number of
sepal
A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 The term ''sepalum'' was coine ...
s in a whorl of the calyx, the number of
petals in a whorl of the corolla, the number of
stamens 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 fila ...
, 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 that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils' ...
. The term may also be used to refer to the number of leaves in a
leaf
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
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, toadshade, 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 No ...
'' 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.
Gallery
See also
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Cyclic flower A cyclic flower is a flower type formed out of a series of whorls; sets of identical organs attached around the axis at the same point. Most flowers consist of a single whorl of sepals termed a calyx; a single whorl of petals termed a corolla; o ...
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Floral diagram
Floral diagram is a graphic representation of flower structure. It shows the number of floral organs, their arrangement and fusion. Different parts of the flower are represented by their respective symbols. Floral diagrams are useful for flower i ...
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Floral formula
A Floral formula is a notation for representing the structure of particular types of flowers. Such notations use numbers, letters and various symbols to convey significant information in a compact form. They may represent the floral form of a part ...
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