Editing Asteraceae (section)

== Variations ==
A ''radiate head'' has disc flowers surrounded by ray flowers. A ''ligulate head'' has all ligulate flowers and no disc flowers. When an Asteraceae flower head has only disc flowers that are either sterile, male, or [[Plant reproductive morphology#Bisexual|bisexual]] (but not female and fertile), it is a ''discoid head''.

''Disciform heads'' possess only disc flowers in their heads, but may produce two different sex types (male or female) within their disciform head.

Some other species produce two different head types: ''staminate'' (all-male), or ''pistillate'' (all-female). In a few unusual species, the "head" will consist of one single disc flower; alternatively, a few species will produce both single-flowered female heads, along with multi-flowered male heads, in their "pollination strategy".<ref name=CDF/>

=== Floral structures<span class="anchor" id="Floral structures"></span> ===
[[File:Carduus floral diagram.svg|thumb|Flower diagram of ''[[Carduus]]'' (Carduoideae) shows (outermost to innermost): subtending bract and stem axis; calyx forming a pappus; fused corolla; stamens fused to corolla; gynoecium with two carpels and one [[locule]]]]
[[File:Senecio mikanioides (delairea odorata).jpg|thumb|Discoid flowerheads of ''[[Delairea odorata]]''.]]
The distinguishing characteristic of Asteraceae is their [[inflorescence]], a type of specialised, composite flower head or ''[[pseudanthium]]'', technically called a calathium or ''[[Pseudanthium|capitulum]]'',<ref name=Beentje/><ref name=Usher/> that may look superficially like a single flower. The ''capitulum'' is a contracted [[raceme]] composed of numerous individual [[Sessility (botany)|sessile]] flowers, called ''florets'', all sharing the same [[Receptacle (botany)|receptacle]].

A set of [[bract]]s forms an [[involucral bract|involucre]] surrounding the base of the capitulum. These are called "phyllaries", or "involucral bracts". They may simulate the sepals of the pseudanthium. These are mostly herbaceous but can also be brightly coloured (e.g. ''[[Helichrysum]]'') or have a scarious (dry and membranous) texture. The phyllaries can be free or fused, and arranged in one to many rows, overlapping like the tiles of a roof (''imbricate'') or not (this variation is important in identification of tribes and genera).

Each floret may be subtended by a bract, called a "palea" or "receptacular bract". These bracts are often called "[[chaff]]". The presence or absence of these bracts, their distribution on the receptacle, and their size and shape are all important diagnostic characteristics for genera and tribes.

The florets have five petals fused at the base to form a [[Corolla (flower)|corolla]] tube and they may be either [[actinomorphic]] or [[zygomorphic]]. ''Disc florets'' are usually actinomorphic, with five petal lips on the rim of the corolla tube. The petal lips may be either very short, or long, in which case they form deeply lobed petals. The latter is the only kind of floret in the [[Carduoideae]], while the first kind is more widespread. ''Ray florets'' are always highly zygomorphic and are characterised by the presence of a ''ligule'', a strap-shaped structure on the edge of the corolla tube consisting of fused petals. In the Asteroideae and other minor subfamilies these are usually borne only on florets at the circumference of the capitulum and have a 3+2 scheme – above the fused corolla tube, three very long fused petals form the ligule, with the other two petals being inconspicuously small. The Cichorioideae has only ray florets, with a 5+0 scheme – all five petals form the ligule. A 4+1 scheme is found in the Barnadesioideae. The tip of the ligule is often divided into teeth, each one representing a petal. Some marginal florets may have no petals at all (filiform floret).

The calyx of the florets may be absent, but when present is always modified into a [[Pappus (botany)|pappus]] of two or more teeth, scales or bristles and this is often involved in the dispersion of the seeds. As with the bracts, the nature of the pappus is an important diagnostic feature.

There are usually four or five [[stamen]]s.<ref name=Spellenberg2001 /> The filaments are fused to the corolla, while the anthers are generally [[connation|connate]] (''syngenesious'' anthers), thus forming a sort of tube around the style (''theca''). They commonly have basal and/or apical appendages. Pollen is released inside the tube and is collected around the growing style, and then, as the style elongates, is pushed out of the tube (''nüdelspritze'').

The [[pistil]] consists of two connate [[carpel]]s. The [[carpel|style]] has two lobes. Stigmatic tissue may be located in the interior surface or form two lateral lines. The [[ovary (plants)|ovary]] is inferior and has only one [[ovule]], with basal [[placentation]].

=== Fruits and seeds ===
In members of the Asteraceae the fruit is [[achene]]-like, and is called a ''cypsela'' (plural ''cypselae''). Although there are two fused carpels, there is only one locule, and only one seed per fruit is formed.<ref name=Spellenberg2001 /> It may sometimes be winged or spiny because the pappus, which is derived from calyx tissue often remains on the fruit (for example in [[dandelion]]). In some species, however, the pappus falls off (for example in ''[[Helianthus]]''). Cypsela [[morphology (biology)|morphology]] is often used to help determine plant relationships at the genus and species level.<ref name=McKenzieEtAl/> The mature seeds usually have little [[endosperm]] or none.<ref name=Judd/>

=== Pollen ===
The pollen of composites is typically echinolophate, a [[Morphology (biology)|morphological]] term meaning "with elaborate systems of ridges and spines dispersed around and between the apertures."<ref name=Tomb1974/>

=== Metabolites ===
In Asteraceae, the energy store is generally in the form of [[inulin]] rather than starch. They produce iso/[[chlorogenic acid]], [[sesquiterpene]] [[lactones]], pentacyclic triterpene alcohols, various [[alkaloid]]s, [[acetylene]]s (cyclic, aromatic, with vinyl end groups), [[tannin]]s. They have [[terpene|terpenoid]] [[essential oil]]s that never contain [[iridoid]]s.<ref name=Stevens/>

Asteraceae produce [[secondary metabolites]], such as [[flavonoid]]s and [[terpenoid]]s. Some of these molecules can inhibit [[protozoa]]n parasites such as ''[[Plasmodium]]'', ''[[Trypanosoma]]'', ''[[Leishmania]]'' and parasitic intestinal worms, and thus have potential in medicine.<ref name=PandaLuyten2018/>