|Copyright: ROBERTO INTILE (rintile)
|Date Taken: 2007-02-06|
|Exposure: f/2.8, 1/200 seconds|
|More Photo Info: [view]|
|Photo Version: Original Version|
|Date Submitted: 2007-02-10 22:14|
|[Note Guidelines] Photographer's Note|
|Plants belonging to the Asteraceae share all the following characteristics (Judd et al., 1999). None of these traits, taken separately, can be considered synapomorphic.|
The inflorescence is an involucrate capitulum (flower head)
Tubular/disc florets are actinomorphic, ligulate/ray florets are zygomorphic
Anthers are syngenesious, i.e. with the stamens fused together at their edges, forming a tube
The ovary has basal arrangement of the ovules
One ovule per ovary
The calyx (sepals) of the florets are modified to form a pappus, a tuft of hairs, which often appears on the mature fruit
The fruit is an achene
In the essential oils Sesquiterpenes are present, but iridoids are lacking.
A typical Asteraceae flower head (here Bidens torta) showing the individual flowers
Flowers of a sunflower with different forms and phases (sterile ray flowers, disc flowers in female, male and unopened phases)The most common characteristic of all these plants is an inflorescence or flower head; a densely packed cluster of many small, individual flowers, usually called florets (meaning "small flowers").
Plants in the family Asteraceae typically have one or both of two kinds of florets. The outer perimeter of a flower head like that of a sunflower is composed of florets possessing a long strap-like petal, termed a ligule; these are the ray florets. The inner portion of the flower head (or disc) is composed of small flowers with tubular corollas; these are the disc florets. The composition of asteraceous inflorescences varies from all ray flowers (like dandelions, genus Taraxacum) to all disc flowers (like pineapple weeds).
The composite nature of the inflorescences of these plants led early taxonomists to call this family the Compositae. Although the rules governing naming conventions for plant families state that the name should come from the type genus, in this case Aster and thus Asteraceae. However, the long prevailing name Compositae is also authorized as an alternative family name (ICBN Art. 18.6).
The numerous genera are divided into about 13 tribes. Only one of these, Lactuceae, is considered distinct enough to be a subfamily (subfamily Cichorioideae); the remainder, which are mostly overlapping, are put in the subfamily Asteroideae (Wagner, Herbst, and Sohmer, 1990).
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