{{Short description|Metric in plant morphology}} '''Merosity''' (from the greek "méros," which means "having parts"{{source needed|reason=I can't find an adjective μέρος.|date=March 2025}}) refers to the number of component parts in a distinct whorl of a plant structure.<ref name="Ronse Decraene and Smets 1994" /> The term is most commonly used in the context of a flower where it refers to the number of sepals 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, or the number of carpels in a whorl of the gynoecium. The term may also be used to refer to the number of leaves in a leaf whorl.
{| class="wikitable" ! scope="col" style="width: 8em;" | ! scope="col" style="width: 16em;" | Noun ! scope="col" style="width: 16em;" | Adjective |- style="text-align: center;" | 2 parts || dimery || dimerous, 2-merous |- style="text-align: center;" | 3 parts || trimery || trimerous, 3-merous |- style="text-align: center;" | 4 parts || tetramery || tetramerous, 4-merous |- style="text-align: center;" | 5 parts || pentamery || pentamerous, 5-merous |- style="text-align: center;" | many parts || polymery || polymerous |- style="text-align: center;" | few parts || oligomery || oligomerous |}
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.<ref name="Ronse Decraene and Smets 1994" />
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'''.<ref name="latindict" /> 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.
{| class="wikitable" ! scope="col" style="width: 8em;" | ! scope="col" style="width: 16em;" | Noun ! scope="col" style="width: 16em;" | Adjective |- style="text-align: center;" | equal parts || isomery || isomerous |- style="text-align: center;" | unequal parts || anisomery || anisomerous |}
==Gallery==
{{multiple image | direction = horizontal | align = left | caption_align = center | total_width = 800
| image1 = Tulip Tulipa clusiana 'Lady Jane' Rock Ledge Flower 2000px.jpg | alt1 = | caption1 = Trimerous flower of ''Tulipa clusiana'' (the three sepals resemble petals)
| image2 = Correa Alba RTBG.jpg | alt2 = | caption2 = Tetramerous flower of ''Correa alba''
| image3 = Crassula ovata RTBG.jpg | alt3 = | caption3 = Pentamerous flower of ''Crassula ovata'' }} {{clear}}
==See also== * Cyclic flower * Floral diagram * Floral formula
==References==
{{Reflist|refs=
<ref name="Ronse Decraene and Smets 1994">{{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}}</ref>
<ref name="latindict">{{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}}</ref>
}}
Category:Plant morphology