Tepal
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In a general sense, a tepal is an element of the perianth of a flower, such as a petal or sepal. The perianth comprises the outer, sterile whorls of a flower. The term tepal is usually used when all segments of a perianth are of similar shape and color (that is, undifferentiated). This happens in the family Magnoliaceae and a number of other primitive flowering plants such as the Amborellaceae and Calycanthaceae.
Merosity
Merosity is a property of whorls of floral perianths that relates how many tepals a whorl of that particular plant has. Types of merosity, according to number of tepals in a perianth whorl, include:
These nouns for the different types of merosity are formed by a prefix derived from Ancient Greek (e.g. tetra- for four tepals) and the suffixed root, -mery, which is derived from Greek meros meaning "part".