My question is as the subject states. Is a ray floret of a composite flower a corolla lobe, and are the corolla the ray florets of the flower head? :)
Hi @elizabeth1067, great questions! This took me a little while to get my head around when I was first learning botany.
The things referred to as “florets” in composites are actually complete flowers (just small), each with its own complete corolla, stamens, style, ovary, and “calyx” modified as pappus of various kinds. The composite family is defined in part by having many such flowers grouped together in heads (=capitula), which are often taken to be single flowers, but are actually “composed” of numerous individual flowers.
Your typical sunflower-like head has a number of ray flowers around the margin (the sun “rays”), surrounding an even larger number of disk flowers in the center. Depending on the species, there can be hundreds of flowers (=florets) in a single “flower-like” head of a composite.
That said, many composite heads are anything but typical. Some are completely missing ray flowers and have only disk flowers (discoid). Members of the dandelion tribe are the opposite, having all ray flowers and no disk flowers. A look through https://www.inaturalist.org/taxa/47604-Asteraceae/browse_photos will give you some idea of the huge variation in composite heads.
Getting back to your questions, the typical ray floret of a sunflower head is a complete flower. The “ray” portion is actually 3 fused lobes of the corolla that are much longer than the other 2 lobes (which are often small and hard to find). You can tell this since the tip of the ray usually has 3 teeth or lobes. In the dandelion tribe, all 5 corolla lobes are fused and elongated to one side as the ray – these have 5 teeth at the ray tips. In heads with disk flowers, each disk corolla is usually more symmetrical with 5 short equal lobes.
Again, there are huge variations from the typical sunflower plan above, which makes the family both great fun and a great challenge to learn.
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Oh, and I forgot to mention the phyllaries, which in a typical sunflower are the green somewhat leaf-like bracts that surround the outside of each head of flowers. If someone is thinking of a head as a single “flower,” then the phyllaries would be akin to a “calyx.” But of course they aren’t – they are leaves modified to collectively help protect the flowers in the head.
Phyllaries are likewise subject to huge variation and modification, up to and including being entirely absent and replaced by other structures instead.
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@jdmore Well that certainly clears things up! :) Seriously, though, very informative.
I had read that each little piece of the disk is a flower, but I didn’t understand that each little “petal” is a flower. For some of the smaller rays, it would seem a microscope, or a good source by someone who has already used one, would be in order to learn to identify the various parts. How about something called Composite Flower Parts and Where to Find Them?
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Composite flowers are everywhere and Asteraceae is one of the most successful plant families now. I don’t think you need a microscope for them, even small ones, they’re nothing like Poaceae where you need to use microscope to properly see flowers, for Asteracea one of the main traits is phyllaries, clear photo of them can get you an id of most of species in it.
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Can this be our new iNat motto?
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Here are some web pages that include labeled diagrams:
https://web.stanford.edu/group/dahlia_genetics/compositae_info.htm
https://www.anbg.gov.au/PLANTFAM/AUST1F.HTM
https://www.cronodon.com/BioTech/asteraceae.html
http://www.svenlandrein.com/systematiccoursepages/images/morphology/jepsonweb/images/composite.jpg
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All of the “dandelion-like” flowers are also composite flowers, and in their case the terminology is somewhat different. Since they do not have distinct rays and disc, all of their “petals” are referred to as strap flowers. Each one is complete with reproductive parts and a single “ray.”
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