Merosity (from the greek "méros," which means "having parts") refers to the number of component parts in a distinct

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane flo ...

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 mechanism ...

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 coined ...

s in a whorl of the calyx, the number of

petal Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corolla''. Petals are usuall ...

s in a whorl of the corolla, the number of

stamen 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 filam ...

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 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) '' pistil ...

. The term may also be used to refer to the number of leaves in a

leaf A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

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'' 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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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

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References