inflorescence [ in-flaw-res-uhns ] noun: 1. the flowering structure consisting of more than one flower, usually comprising distinct individual flowers 2. the way flowers are arranged or develop on a stalk 3. the budding and flowering of a plant
Some plants produce solitary flowers–one flower per stem. Others produce a cluster of flowers or inflorescences. They are grouped by the arrangement of flowers on the stalk and by the sequence of anthesis, or opening of the flower bud, which occurs in two forms, determinate and indeterminate. Determinate (or cymose) flowering plants have the oldest flower at the top of the main axis (rachis or stalk), meaning the terminal bud stops growing and lateral flowers are produced from axillary buds lower on the stem. Indeterminate (or racemose) plants flower with the youngest bud at the top of the main axis.
These inflorescences can take many forms, including cymes, spikes, racemes, panicles, thyrses, catkins or aments, spadices, corymbs, umbels, and capitulums or heads. Forms can be simple, compound, or mixed.
Can you identify the types of determinate inflorescence below?
Can you identify the types of indeterminate inflorescence below?
Some taxonomy scholars, particularly of grasses, note that there is not always consistency in application of the various terms such as spike, raceme, panicle, and thyrse. For example, various botanical references either describe the inflorescence of Aesculus pavia (red buckeye) as a panicle or as a thyrse. Also, compare two plants with the Latin epithet “spicata” or spiked. An example of a determinate inflorescence in spike form is the familiar native Liatris spicata (blazing star or gayfeather) shown below with spent flowers at the top of the spike. An indeterminate plant of a similar form is annual Celosia spicata (wheat celosia), but it blooms from the bottom up with anticipation of new buds forming until frost.
Indeterminate plants include certain tomato plants and some grasses; and because the new flowers occur at the tops of stems, they can continue to produce new growth and new flowers, and at least in theory, remain visibly attractive for longer seasons.
For home gardeners, it is good to know whether the tomato plants you are growing are determinate or indeterminate, as this affects fruit production and timing. Indeterminate tomatoes will generally have a longer bearing season, while determinate crops tend to ripen around the same time.
Botany 115 Terminology: Inflorescence Terminology Part 1. Wayne’s Word. © W.P. Armstrong. [accessed 5 April 2021].
The Flower: Vocabulary-o-Rama! BIL 226 – Lecture 17. College of Art and Sciences. University of Miami. [accessed 5 April 2021].
Robertson, K. Prairie Plant Terminology–Inflorescences (Flower clusters). The Tall Grass Prarie in Illinois. Illinois Natural History Survey. © 2021 University of Illinois Board of Trustees.