Wspólna cecha rodziny Asteraceae jest wyksztalcanie swoistego typu kwiatostanu,
zwanego koszyczkiem (calathium). Atrybutami koszyczka sa: dno kwiatostanowe, otaczajca je okrywa zmodyfikowanych listków, kwiatki i wystêpujce czasem przykwiatki

Ryc. 1. Callistephus chinensis schemat budowy koszyczka l listki okrywy; 2 dno kwiatosta nowe (receptaculum); 3 kwiaty promieniste (flores radii); 4 kwiaty dyskowe (flores disci).
Fig. 1. Callistephus chinensis a diagram of head structure: 1 involucre bracts; 2 receptacle;
3 ray florets; 4 disc florets.


Okrywa (involucrum). Okrywê koszyczka tworzy kilka szeregów zró¿nicowanych
listków.

https://pbsociety.org.pl/journals/index.php/aa/article/viewF...

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Some members of the Asteraceae have only one row of involucral bracts
http://herbarium.usu.edu/taxa/asteraceae.htm
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Involucral bracts

Beggar-tick (Bidens comosa)
Bracts that appear in a whorl subtending an inflorescence are collectively called an involucre. An involucre is a common feature beneath the inflorescences of many Apiaceae, Asteraceae, Dipsacaceae and Polygonaceae. Each flower in an inflorescence may have its own whorl of bracts, in this case called an involucel. In this case they may be called chaff, paleas, or receptacular bracts and are usually minute scales or bristles. Many asteraceous plants have bracts at the base of each inflorescence.
http://en.wikipedia.org/wiki/Bract
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The middle involucral bracts are small and scale-like; they form a basket enclosing the flowers.
https://books.google.com/books?id=QHO1BgAAQBAJ&pg=PA10&lpg=P...

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. The cypselas remain in a basket formed by the erect involucral bracts

http://www.luontoportti.com/suomi/en/kukkakasvit/nipplewort
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Note added at 11 hrs (2015-04-11 15:08:34 GMT)
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Capitulum jest innym określeniem head structure
A compact head of a structure, in particular a dense, flat cluster of small flowers or florets, as in plants of the daisy family.
http://www.oxforddictionaries.com/us/definition/american_eng...
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The involucre of bracts subtending a capitulum, may be arranged in a single whorl as in Coreopsis or many whorls as in Vernonia and Eclipta ..
https://books.google.com/books?id=mnGS2ZE6iA0C&pg=PA243&lpg=...
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(of a bract) extend under (a flower) so as to support or enfold it.
https://books.google.com/books?id=mnGS2ZE6iA0C&pg=PA243&lpg=...
http://www.oxforddictionaries.com/us/definition/american_eng...