Many capitulum inflorescences, several corymb inflorescences with capitulum inflorescences as the end nodes of each corymb inflorescence, or one compound corymb inflorescence with capitulum inflorescences as the end nodes?
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$\begingroup$ A picture would be of great help here. $\endgroup$– DarlingtoniaApr 24 at 23:20
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$\begingroup$ @Darlingtonia picture uploaded. Thanks. $\endgroup$– WilliamApr 25 at 1:38
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1$\begingroup$ Thank you. I'm a little concerned this is a homework question. What have you found about capitula (capitulums?) and corymbs that might help with the question? $\endgroup$– DarlingtoniaApr 27 at 16:36
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$\begingroup$ @Darlingtonia I read some materials that say Sonchus oleraceus's capitulums are arranged as corymbs or raceme at the end of stem. I'm confused what on earth the inflorescence of Sonchus oleraceus is. Isn't the inflorescence of a plant fixed? $\endgroup$– WilliamApr 28 at 1:33
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1 Answer
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A flowering plant's inflorescence is the grouping of flower clusters on the plant. Inflorescences are categorized based on the architecture of the arrangement of flowers within them.
As members of the sunflower or daisy family, Asteraceae, Sonchus has it's flowers compressed into tight heads called capitula. A sunflower might casually appear to be a single flower, but close examination will reveal that it is made of many (dozens in the case of Sonchus) smaller flowers. In the photo above, each yellow petal, including those in the interior of the disc, originates from a separate flower. As such, the inflorescence of Sonchus is a capitulum.
However, Asteraceae is an extremely diverse family, and the arrangement of capitula can be an important character in classifying and identifying these plants. Because of this, the same inflorescence terms applied to a group of flowers can also be applied to a group of capitula. In Sonchus one can (often) call the arrangement of capitula a corymb*. One definition of corymb is "a flat-topped or round-topped inflorescence, racemose, but with the lower pedicels longer than the upper".
So, strictly, the inflorescence of Sonchus olearaceus is a capitulum, and the capitula are arranged in (approximate) corymbs.
*The first resource I found listed Sochus as "corymbiform to subumbelliform" which means, roughly, ranging from a corymb (but maybe not exactly) to not-quite-an-umbel.
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$\begingroup$ Thank you for your analysis. I think there exists a difference between an inflorescence and a sub-inflorescence in an inflorescence. For example, a sub-inflorescence of a compound corymb is also a corymb. As to Sonchus olearaceus, the capitulum seems a sub-inflorescence, not an independent inflorescence, but I did not find the name of this type of compound inflorescence. All the named compound inflorescences I find have sub-inflorescence the same inflorescence type as the compound inflorescence itself such as compound umbel, compound corymb, and compound racemose. $\endgroup$– WilliamApr 29 at 8:35