Merosity (from the greek "méros," which means "having parts") refers to the number of component parts in a distinctwhorl of a plant structure.[1] The term is most commonly used in the context of aflower where it refers to the number ofsepals in a whorl of the calyx, the number ofpetals in a whorl of the corolla, the number ofstamens in a whorl of theandroecium, or the number of carpels in a whorl of thegynoecium. The term may also be used to refer to the number of leaves in aleaf whorl.
| Noun | Adjective | |
|---|---|---|
| 2 parts | dimery | dimerous, 2-merous |
| 3 parts | trimery | trimerous, 3-merous |
| 4 parts | tetramery | tetramerous, 4-merous |
| 5 parts | pentamery | pentamerous, 5-merous |
| many parts | polymery | polymerous |
| few parts | oligomery | oligomerous |
The adjectiven-merous refers to a whorl ofn parts, wheren 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.[1]
If all of the whorls in a given floral arrangement have the same merosity, the flower is said to beisomerous, otherwise the flower isanisomerous.[2] 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.
| Noun | Adjective | |
|---|---|---|
| equal parts | isomery | isomerous |
| unequal parts | anisomery | anisomerous |
