Asteraceae (/ˌæstəˈreɪsi.iː,-ˌaɪ/) is a largefamily offlowering plants that consists of over 32,000 known species in over 1,900 genera within theorderAsterales. The number of species in Asteraceae is rivaled only by theOrchidaceae, and which is the larger family is unclear as the quantity ofextant species in each family is unknown. The Asteraceae were first described in the year 1740 and given the original nameCompositae.[6] The family is commonly known as theaster,daisy,composite, orsunflower family.
Asteraceae is an economically important family, providing food staples, garden plants, and herbal medicines. Species outside of their native ranges can becomeweedy orinvasive.
Members of the Asteraceae are mostly herbaceous plants, but some shrubs, vines, and trees (such asLachanodes arborea) do exist. Asteraceae species are generally easy to distinguish from other plants because of their uniqueinflorescence and other shared characteristics, such as the joined anthers of thestamens.[7] Nonetheless, determining genera and species of some groups such asHieracium is notoriously difficult (see "damned yellow composite" for example).[8]
Members of the family Asteraceae generally producetaproots, but sometimes they possess fibrous root systems. Some species have underground stems in the form ofcaudices orrhizomes. These can be fleshy or woody depending on the species.[6]
The stems are herbaceous, aerial, branched, and cylindrical with glandular hairs, usually erect, but can be prostrate to ascending. The stems can contain secretory canals withresin,[6] orlatex, which is particularly common among theCichorioideae.[9]
Nearly all Asteraceae bear their flowers in dense flower heads calledcapitula. They are surrounded byinvolucral bracts, and when viewed from a distance, each capitulum may appear to be a single flower. Enlarged outer (peripheral) flowers in the capitulum may resemble petals, and the involucral bracts may look like a calyx.[10] Notable exceptions includeHecastocleis shockleyi (the only species in the subfamily Hecastocleidoideae)[11] and the species of the genusCorymbium (the only genus in the subfamily Corymbioideae),[12] which have one-flowered bisexual capitulas,Gundelia with one-flowered unisexual capitulas,[13] andGymnarrhena micrantha with one-flowered female capitulas and few flowered male capitulas.[14]
A typical Asteraceae flower head showing the (five) individual ray florets and the (approximately 16) disk florets of a specimen of (Bidens torta)
In plants of the Asteraceae, what appears to be a single "daisy"-type flower is actually a composite of several much smaller flowers, known as thecapitulum orhead. By visually presenting as a single flower, the capitulum functions in attractingpollinators, in the same manner that other "showy" flowering plants in numerous other, older, plant families have evolved to attract pollinators. The previous name for the family,Compositae, reflects the fact that what appears to be a single floral entity is in fact acomposite of much smaller flowers.[15]
The "petals" or "sunrays" in an "asteraceous" head are in fact individual strap-shaped[16] flowers calledray flowers orray florets, and the "sun disk" is made up of smaller,radially symmetric, individual flowers calleddisc flowers ordisc florets. The wordaster means "star" in Greek, referring to the appearance of most family members as a "celestial body with rays".The capitulum, which often appears to be a single flower, is often referred to as ahead.[17] In some species, the entire head is able to pivot its floral stem in the course of the day to track the sun (like a "smart" solar panel), thus maximizing the reflectivity of the entire floral unit and further attracting flying pollinators.[15]
Nearest to the flower stem lie a series of small, usually green, scale-likebracts. These are known asphyllaries; collectively, they form theinvolucre, which serves to protect the immature head of florets during its development.[15]: 29 The individual florets are arranged atop a dome-like structure called thereceptacle.[15]
The individual florets in a head consist, developmentally, of five fusedpetals (rarely four); instead ofsepals, they have threadlike, hairy, or bristly structures,[17] known collectively as apappus, (pluralpappi). The pappus surrounds the ovary and can, when mature and attached to a seed, adhere to animal fur or be carried by air currents, aiding inseed dispersal. The whitish, fluffy head of adandelion, commonly blown on by children, consists of numerous seeds resting on the receptacle, each seed attached to its pappus. The pappi provide a parachute-like structure to help the seed travel from its point of origin to a more hospitable site.[15]
Schemes and floral diagrams of the different floret types of the Asteraceae:Leucanthemum vulgare: a = disc flower; b = ray flower. 1 –style withstigmas 2 –anthers 3 – corolla (petals); typically, in the ray flower, three petals are joined to form a strap (in other species, five petals can fuse to form aligule) 4 – reducedcalyx 4’ –Carduus acanthoides (left shaded circle):pappus: in many Asteraceae species, the calyx develops as a fibrous or bristly pappus 5 –inferior ovary: fused ovary consisting of twocarpels, containing oneabaxialovule (basal placentation).
Aray flower is a two- or three-lobed, strap-shaped, individual flower, found in the head of most members of the Asteraceae.[15][16] Thecorolla of the ray flower may have two tiny,vestigial teeth, opposite to the three-lobed strap, or tongue, indicating its evolution by fusion from an ancestral, five-part corolla. In some species, the 3:2 arrangement is reversed, with two lobes, and zero or three tiny teeth visible opposite the tongue.
Aligulate flower is a five-lobed, strap-shaped, individual flower found in the heads of certain other asteraceous species.[15] Aligule is the strap-shaped tongue of the corolla of either a ray flower or of a ligulate flower.[clarification needed][example needed][16] Adisk flower (ordisc flower) is a radially symmetric individual flower in the head, which is ringed by the ray flowers when both are present.[15][16] In some species, ray flowers may be arranged around the disc in irregular symmetry, or with a weaklybilaterally symmetric arrangement.[15]
Aradiate head has disc flowers surrounded by ray flowers. Aligulate head has all ligulate flowers and no disc flowers. When an Asteraceae flower head has only disc flowers that are either sterile, male, orbisexual (but not female and fertile), it is adiscoid 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), orpistillate (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".[15]
Flower diagram ofCarduus (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 oneloculeDiscoid flowerheads ofDelairea odorata.
The distinguishing characteristic of Asteraceae is theirinflorescence, a type of specialised, composite flower head orpseudanthium, technically called a calathium orcapitulum,[18][19] that may look superficially like a single flower. Thecapitulum is a contractedraceme composed of numerous individualsessileflowers, calledflorets, all sharing the samereceptacle.
A set ofbracts forms aninvolucre 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 acorolla tube and they may be eitheractinomorphic orzygomorphic.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 theCarduoideae, while the first kind is more widespread.Ray florets are always highly zygomorphic and are characterised by the presence of aligule, 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 apappus 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 fivestamens.[17] The filaments are fused to the corolla, while the anthers are generallyconnate (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).
Thepistil consists of two connatecarpels. Thestyle has two lobes. Stigmatic tissue may be located in the interior surface or form two lateral lines. Theovary is inferior and has only oneovule, with basalplacentation.
In members of the Asteraceae the fruit isachene-like, and is called acypsela (pluralcypselae). Although there are two fused carpels, there is only one locule, and only oneseed per fruit is formed.[17] It may sometimes be winged or spiny because the pappus, which is derived from calyx tissue often remains on the fruit (for example indandelion). In some species, however, the pappus falls off (for example inHelianthus). Cypselamorphology is often used to help determine plant relationships at the genus and species level.[20] The matureseeds usually have littleendosperm or none.[7]
The pollen of composites is typically echinolophate, amorphological term meaning "with elaborate systems of ridges and spines dispersed around and between the apertures."[21]
Compositae, the original name for Asteraceae, were first described in 1740 by Dutch botanistAdriaan van Royen.[24]: 117–118 Traditionally, two subfamilies were recognised:Asteroideae (or Tubuliflorae) andCichorioideae (or Liguliflorae).[25]: 242 The latter has been shown to be extensivelyparaphyletic, and has now been divided into 12 subfamilies, but the former still stands.[26][needs update] The study of this family is known assynantherology.
Thephylogenetic tree of subfamilies presented below is based on Panero &Funk (2002)[26] updated in 2014,[27] and now also includes the monotypicFamatinanthoideae.[27][28][29][needs update]The diamond (♦) denotes a very poorly supportednode (<50% bootstrap support), the dot (•) a poorly supported node (<80%).[22]
Asteroideae: 1,130 genera and 16,200 species. Worldwide.
The family includes over 32,000 currently accepted species, in over 1,900 genera (list) in 13 subfamilies.[4][needs update] The number of species in the family Asteraceae is rivaled only by Orchidaceae.[22][30] Which is the larger family is unclear, because of the uncertainty about how manyextant species each family includes.[citation needed] The four subfamiliesAsteroideae,Cichorioideae,Carduoideae andMutisioideae contain 99% of the species diversity of the whole family (approximately 70%, 14%, 11% and 3% respectively).[citation needed]
Because of themorphological complexity exhibited by this family, agreeing on generic circumscriptions has often been difficult fortaxonomists. As a result, several of these genera have required multiple revisions.[7]
The oldest known fossils of members of Asteraceae are pollen grains from theLate Cretaceous ofAntarctica, dated to ~76–66 mya (Campanian toMaastrichtian) and assigned to the extant genusDasyphyllum. Barreda,et al. (2015) estimated that thecrown group of Asteraceae evolved at least 85.9 mya (Late Cretaceous,Santonian) with a stem node age of 88–89 mya (Late Cretaceous,Coniacian).[1]
It is not known whether the precise cause of their great success was the development of the highly specialised capitulum, their ability to store energy asfructans (mainlyinulin), which is an advantage in relatively dry zones, or some combination of these and possibly other factors.[22] Heterocarpy, or the ability to produce different fruit morphs, has evolved and is common in Asteraceae. It allows seeds to be dispersed over varying distances and each is adapted to different environments, increasing chances of survival.[31]
The original name Compositae is still valid under the International Code of Nomenclature for algae, fungi, and plants.[32] It refers to the "composite" nature of the capitula, which consist of a few or many individual flowers.[citation needed]
The vernacular namedaisy, widely applied to members of this family, is derived from theOld English name of the daisy (Bellis perennis):dæġes ēaġe, meaning "day's eye". This is because the petals open at dawn and close at dusk.[34]
Asteraceae species have a widespread distribution, from subpolar to tropical regions in a wide variety of habitats. Most occur in hot desert and cold or hot semi-desert climates, and they are found on every continent but Antarctica. They are especially numerous in tropical and subtropical regions (notablyCentral America, easternBrazil, theMediterranean,the Levant,southern Africa,central Asia, andsouthwestern China).[30] The largest proportion of the species occur in the arid and semi-arid regions of subtropical and lower temperate latitudes.[6] The Asteraceae family comprises 10% of all flowering plant species.[8]
Asteraceae are especially common in open and dry environments.[7] Many members of Asteraceae arepollinated by insects, which explains their value in attractingbeneficial insects, butanemophily is also present (e.g.Ambrosia,Artemisia). There are manyapomictic species in the family.
Seeds are ordinarily dispersed intact with the fruiting body, the cypsela.Anemochory (wind dispersal) is common, assisted by a hairy pappus.Epizoochory is another common method, in which the dispersal unit, a single cypsela (e.g.Bidens) or entire capitulum (e.g.Arctium) has hooks, spines or some structure to attach to the fur or plumage (or even clothes, as in the photo) of an animal just to fall off later far from its mother plant.
Plants are used as herbs and inherbal teas and other beverages. Chamomile, for example, comes from two different species: the annualMatricaria chamomilla (German chamomile) and the perennialChamaemelum nobile (Roman chamomile).Calendula (known as pot marigold) is grown commercially for herbal teas andpotpourri.Echinacea is used as a medicinal tea. The wormwood genusArtemisia includesabsinthe (A. absinthium) andtarragon (A. dracunculus). Winter tarragon (Tagetes lucida), is commonly grown and used as a tarragon substitute in climates where tarragon will not survive.[44]
Many species of this family possess medicinal properties and are used as traditionalantiparasitic medicine.[23]
Members of the family are also commonly featured in medical and phytochemical journals because thesesquiterpenelactone compounds contained within them are an important cause ofallergic contact dermatitis. Allergy to these compounds is the leading cause of allergic contact dermatitis in florists in the US.[47]Pollen from ragweedAmbrosia is among the main causes of so-calledhay fever in theUnited States.[48]
Several members of the family are copiousnectar producers[45] and are useful for evaluatingpollinator populations during their bloom.[citation needed]Centaurea (knapweed),Helianthus annuus (domestic sunflower), and some species ofSolidago (goldenrod) are major "honey plants" forbeekeepers.Solidago produces relatively high proteinpollen, which helpshoney bees over winter.[49]
^abcdMacKay, Pam (2013).Mojave Desert Wildflowers: A Field Guide To Wildflowers, Trees, And Shrubs Of The Mojave Desert, Including The Mojave National Preserve, Death Valley National Park, and Joshua Tree National Park (Wildflower Series). Guilford, Connecticut:FalconGuides. p. 35 (figure 5).ISBN978-0762780334.
^abPanero, Jose L.; Crozier, Bonnie S. (27 January 2012)."Asteraceae. Sunflowers, daisies".The Tree of Life Web Project (tolweb.org).Archived from the original on 21 January 2022. Retrieved16 February 2021.
^"daisy, n.".Home : Oxford English Dictionary.OED Online. Oxford University Press. March 2021.Archived from the original on 15 January 2023. Retrieved23 April 2021.
^"Tansy ragwortJacobaea vulgaris".Washington State Noxious Weed Control Board (www.nwcb.wa.gov).Archived from the original on 4 December 2020. Retrieved21 January 2021.
^"Taraxacum officinale: dandelion".Invasive Plant Atlas of the United States (www.invasiveplantatlas.org).Archived from the original on 23 October 2012. Retrieved10 September 2012.
^"Senecio angulatus – climbing groundsel".Brisbane City Council weed identification tool (weeds.brisbane.qld.gov.au). Brisbane, Queensland, Australia: Brisbane City Council. Archived fromthe original on 2 March 2021. Retrieved16 February 2021.
^Odom, R.B.; James, W.D.; Berger, T.G. (2000).Andrews' Diseases of the Skin: Clinical Dermatology. Philadelphia, Pennsylvania:W.B. Saunders Company. p. 1135.ISBN978-0721658322.
^Asthma and Allergy Foundation of America."Ragweed Allergy".www.aafa.org. Archived fromthe original on 7 October 2007. Retrieved10 November 2007.
^"Five Plants to Help Pollinators".www.storey.com. The Xerces Society. 2016.Archived from the original on 22 September 2020. Retrieved2 June 2020.Goldenrods are among the most important late-season pollinator plants.
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