All these terms denote parts of a flower, a common word dear to the hearts of gardeners, who often incorporate plants into their gardens based on the color, size, beauty, or rarity of their blooms. But flowers, often the showiest parts of plants, are not there to please the human eye. Their true function is sexual reproduction; hence they contain the male whorl—the androecium—that produces the pollen and/or the female whorl—the gynoecium—that produces the seed plus accessory parts such as petals, sepals, and nectar glands. Their fragrance, form, color, and other qualities are meant to attract pollinators that help ensure the species continues.
perianth [ PER-ee-anth ] noun: the outer structure (whorls) of a flower collectively comprised of the calyx and corolla, especially when the two whorls are fused
- The perianth functions as a protective envelope, and indeed the term is derived from Latin words meaning “around the anthers.”
- The calyx and corolla can be distinctive or similar in appearance. When there is no differentiation between the sepals and petals in a perianth (as in the flowers of Uvularia grandiflora), then each segment of the perianth is called a tepal.
calyx [ KAY-liks, KAL-iks ] noun, plural calyxes or calyces: the sometimes-green outer whorl of the perianth consisting of separate or fused sepals
corolla [ kuh–ROL–uh ] noun: all the petals of a flower collectively, whether distinct or connate (fused); the inner whorl of the perianth
- From the Latin word for garland or crown, the corolla forms a ring around the reproductive organs. It is generally surrounded by the outer whorl of protective sepals called the calyx.
petal [ PET-l ] noun: segment of the corolla of a flower, often brightly colored or white
- Petals may contain perfume or nectar (such as in the nectar spurs in columbine or in the tubular nectaries in hellebores) as well as visual cues, such as signals, to attract pollinators.
- The number of petals on a flower is often used in the identification of plant families and genera. Flowers of dicots typically have sepals and/or petals in multiples of four or five. Monocots typically have these floral parts in multiples of three.
- Some species, like irises, redbuds (Cercis), some genera of the Lamiaceae (mint family), and members of the Asteraceae (aster or composite family), have petals with “specialized” names. Other species, like dogwood (Cornus) have structures that appear to be petals but are really petaloid bracts.
sepal [ SEE-puhl ] noun: small, usually green, leaf-like structure on the base of the flower; part of the calyx
- Sepals protect the flower bud and its reproductive organs from drying out or becoming oversaturated with water. After the petals of the bloom have withered, sepals may persist to support the fruit. In the Asteraceae, a modified calyx is called a pappus and serves as an appendage to its fruit, the cypsela, aiding in its dispersal.
- Bracts, like epicalyxes and involucres that subtend flowers or inflorescences, can sometimes be mistaken for green sepals.
- Sepals that are colorful or function as petals are sometimes described as petaloid, as in hellebores or as in clematis and the sterile flowers of hydrangea, both of which are apetalous (lacking petals). The sepals of some flowers may have scent glands or nectar spurs (such as Impatiens capensis).
tepal [ TEE-puhl, TEP–uhl ] noun: a part of a perianth in which there is no differentiation between petals and sepals; one of the modified leaves that make up an undifferentiated perianth, as in many monocots
- Trying to discern whether a flower has tepals, or petals and petaloid sepals, may not be as easy as the definition implies. The Floras of North America and Virginia both agree that Hemerocallis has six tepals, however the American Daylily Society recognizes a single daylily flower as having three petals and three sepals, and, indeed, the distinction is noticeable in some daylily cultivars like Hemerocallis ‘Final Touch,’ pictured above.The Floras differ on their treatment of other genera. For example, the Flora of North America describes Lilium as having “perianth campanulate, funnelform, or with sepals and petals strongly reflexed in form of a “Turk’s-cap;” while the Flora of Virginia (Weakley et al., 2012) describes Lilium “perianths campanulate or funnelform, 6-merous; tepals clawed or not,…” Likewise the Flora of North America description for Magnolia reads: “Flowers protogynous, appearing with or before leaves; tepals 9-15, petaloid,” while the Flora of Virginia (Weakley et al., 2012) says: “Flowers solitary, large, fragrant; sepals 3; petals 6–12, in 3 whorls, similar or scarcely differentiated.” Like many things in botany, experts do not always agree.
References
Flower Forms. American Daylily Society. American Hemerocallis Society, Inc. (accessed March 16, 2025).
Illinois Wildflowers, © 2002-2020 by John Hilty. (http://www.illinoiswildflowers.info/index.htm accessed March 15–16, 2025).
Meyer FG. Magnolia. FNA Volume 3. Flora of North America Association. (accessed March 16, 2025).
Schreiber B. March 16, 2021. Ask an Expert: Hellebores! Hoyt Arboretum.
Skinner MW. Lilium. FNA Volume 26. Flora of North America Association. (accessed March 16, 2025).
Straley GB, Utech FH. Hemerocallis. FNA Volume 26. Flora of North America Association. (accessed March 16, 2025).
Waters MT, Tiley AMM, Kramer EM, Meerow AW, Langdale JA, Scotland RW. 2013. The corona of the daffodil Narcissus bulbocodium shares stamen-like identity and is distinct from the orthodox floral whorls. the plant journal. 74(4): 615-625. doi.org: 10.1111/tpj.12150
Weakley AS, Ludwig JC, Townsend JF. 2012. Flora of Virginia. pages 710, 1004, 1157, and 1355.