cypsela [ SIP-suh-luh ] noun, plural cypselae [ SIP-suh-lee]: a one-seeded, indehiscent, dry fruit formed from an inferior ovary and with a fused calyx, characteristic of the Asteraceae
Unlike the internationally recognized terms of taxonomy (the orderly classification of plants), no agreed upon standards exist for naming fruits. Almost 100 types of fruit have been described since 1751 when Carl Linnaeus identified eight different fruits in his Philosophia Botanica, the first textbook of descriptive systematic botany. Today about 15 different fruit types, including the eight identified by Linnaeus, are widely accepted, although disagreement persists in the definitions of some, especially achene and nut.
Some points of contention include whether definitions of fruit should be narrow or broad and whether a fruit should be defined as just the ripened ovary or whether it can also include the floral parts that develop into structures to help disseminate the seeds (anthocarps).
That brings us to the fruits of the Asteraceae (commonly called the aster, composite, daisy, or sunflower family). Each develops from an inferior ovary, which lies below the attachment of petals, sepals, and stamens to the receptacle, the part of the plant that connects the flower to the stem. In 1813, Charles-François Brisseau de Mirbel coined the term cypsela for this fruit type and described it as “crowned by the calyx” (Marzinek et al. 2008). In other words, in addition to the ovary, Mirbel included those floral parts that develop into pappi to aid in seed dispersal.
This definition distinguished the Asteraceae fruit from achenes that develop from a superior ovary, which is situated above the attachment of other floral parts, and are joined to the ovary wall (pericarp) at a single point. Despite the basic morphological difference (origination in an inferior versus superior ovary), cypsela is not among the widely accepted fruit types. The lack of agreement as to what constitutes a fruit and the inconsistency (or flexibility) in the definition of achene, still finds some scientists, botanical references, and web sites using achene interchangeably with cypsela when describing the fruits of the Asteraceae.
Left to right: Erechtites hieraciifolius, Heliopsis helianthoides, Packera aurea,
Solidago rugosa ‘Fireworks,’ Symphyotrichum cordifolium,Taraxacum erythrospermum.
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References
Marzinek J, De-Paula OC, Oliveira DMT. 2008. Cypsela or achene? Refining terminology by considering anatomical and historical factors. Brazilian Journal of Botany. 31(3).
Spjut, RW. 2003–2015. A Systematic Treatment of Fruit Types. © The World Botanical Associates. [accessed October 10, 2022].
Weakley AS, Ludwig JC, Townsend JF. 2012. Flora of Virginia. Botanical Research Institute of Texas.