umbel [ UHM-buhl ] noun: a racemose inflorescence in which flower stalks extend from a common point to form a flat or rounded flower cluster characteristic of the Apiaceae (carrot family)
umbellate [ UHM-buh-lit, -leyt, uhm-BEL-it ] adjective: bearing, consisting of, or arranged in umbels; resembling an umbel in form
umbellet [ UHM-buh-lit ] or umbellule [ UHM-buhl-yool, uhm-BEL-yool ] noun: one of the secondary umbels in a compound umbel
umbelliform [ um-BEL-uh-fawrm ] adjective: resembling an umbel in form
A cluster of flowers is called an inflorescence. The most common types of inflorescences—racemes and panicles—occur widely across plant families. Even the most casual observer is likely acquainted with at least a few examples. But what of an umbel?
Those who grow culinary gardens are familiar with umbels. The Apiaceae (carrot family), also known as the Umbelliferae (the umbel-bearing family), includes many well-known herbs such as caraway, cilantro, dill, fennel, and parsley as well as vegetables like carrot and celery.
The word umbel is from the Latin umbella, which translates to “parasol or sunshade.” Indeed, if you want to envision an umbel, then think of a parasol or umbrella, to which its structure is similar.
In a simple umbel, the peduncle, the main stalk that supports the flower cluster, would be analogous to the part of the umbrella shaft just below the raised runner. Pedicels, the stalks that support the individual flowers, radiate out from a central point at the tip of the peduncle, creating a rounded or flat-topped cluster—much like the stretchers of an umbrella fan out from the runner to support the ribs, giving the umbrella its shape. That central point of attachment, a highly compressed axis or rachis, is what distinguishes an umbel from a raceme (Weberling, 1992).
Umbels can also have a compound structure, which is the most common form. As in simple umbels, the peduncle supports the entire inflorescence. However, at the central point of attachment, rays—rather than pedicels—radiate outward. At the tips of the rays, umbellets—smaller, secondary umbels—arise again from a central point. True umbels are racemose or indeterminate, meaning that the flowers open from the periphery to the center or from the base of the axis to the apex.
True Compound Umbels of the Apiaceae
A single large compound umbel of Anethum graveolens (dill) can produce over 600 flowers in which each of up to ~25 rays terminate in a secondary umbel (umbellet) of up to ~25 tiny yellow flowers with very incurved petals. Note the highly compressed rachis to which the rays attach.
A compound umbel—flat-topped to gently rounded—of Foeniculum vulgare (fennel) can hold 1500+ flowers in groups of ~14–39 in umbellets emanating from up to ~40 unequal rays. Like dill and golden-alexanders, fennel is a host plant to the black swallowtail butterfly whose larva is pictured above.
Flat-topped flower clusters of native Zizia aurea (golden-alexanders) are arranged in a compound umbel with ~10–20 umbellets each with ~10–21 tiny flowers of which the central one is (nearly) sessile. Fruit in the form of schizocarps follow.
Some sources refer to the inflorescences of Allium (onion- or garlic-scented bulbous herbs) and Asclepias (milkweed) as umbels. However, the Flora of Virginia describes the inflorescences of the Amaryllidaceae (the family in which Alliums reside) as “composed of contracted helicoid cymes and appearing to be an umbel” and those of Asclepias as “simple or cymose umbels.” The Flora of North America [Online] describes Alliums as umbellate and Ascelpias as umbelliform. So, although flower clusters in these two genera may resemble an umbel in structure or form, some botanical authorities consider them to be developmentally cymose or determinate.
Umbellate or Umbelliform Inflorescences
The umbel or umbel-like structure—whether globose, like star of Persia; dome-shaped, like garlic chives and milkweed; or flat-topped, like dill, fennel, and golden-alexanders—provides an attractive foraging platform for pollinators. The clustering of many flowers together allows bees, beetles, flies, and lepidopterans (butterflies and moths) to gather pollen or nectar more efficiently, especially if they can save energy by walking from flower to flower.
References
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico [Online]. 25+ vols. New York and Oxford. http://beta.floranorthamerica.org. Accessed April 9–13, 2025.
Michaels T, Clark M, Hoover E, Irish L, Smith A, Tepe E. 2022. 4.1 GROWTH PATTERNS AND INFLORESCENCES. The Science of Plants. University of Minnesota Libraries Publishing.
Rickett HW. 1944. “The Classification of Inflorescences.” Botanical Review 10, no. 3 (1944): 187–231. http://www.jstor.org/stable/4353301.
Watson L, Dallwitz MJ. 1992 onwards. The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000. https://www-archiv.fdm.uni-hamburg.de/b-online/delta/angio/index.htm. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991).
Weakley AS, Ludwig JC, Townsend JF. 2012. Flora of Virginia. Botanical Research Institute of Texas. Pages 254 and 990.
Weberling F. 1992. Morphology of Flowers and Inflorescences. Cambridge Univeristy Press. Page 205. ISBN: 9780521438322