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 Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

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 Etymology The term ''sepalum'' ...

s in a whorl of the calyx, the number of

petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...

s in a whorl of the corolla, the number of

stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

s in a whorl of the

androecium The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

, or the number of carpels in a whorl of the

gynoecium Gynoecium (; ; : gynoecia) 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 (botany), whorl of a flower; it consists ...

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

leaf A leaf (: leaves) is a principal appendage of the plant stem, stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leav ...

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. 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 , bibcode=1994PSyEv.191...83R , url=https://www.academia.edu/25486804 , 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