Asteraceae
Encyclopedia
The Asteraceae or Compositae (commonly referred to as the aster, daisy, or sunflower family), is an exceedingly large and widespread family
of vascular plant
s. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies. Along with the Orchidaceae
, this makes it one of the two largest flowering plant families in the world. However, selecting which of the two families is larger has yet to be been done conclusively, owing to the uncertainty around exactly how many species are in each group. The largest composite genera are Senecio
(1,000 species), Vernonia
(1,000 species), Centaurea
(700 species), Cousinia
(600 species), Helichrysum (550 species), and Artemesia
(550 species).
Most members of Asteraceae are herbaceous, but a significant number are also shrubs, vines and trees. The family is distributed throughout the world, and is most common in the arid
and semi-arid regions of subtropical and lower temperate latitudes.
Many economically important products come from composites, including cooking oil
s, lettuce
, sunflower seed
s, artichoke
s, sweetening agents, and tea
s. Several genera are also very popular with the horticultural
community, these include marigolds, chrysanthemum
s, dahlia
s, zinnia
s, and helenium
s.
, a special type of pseudanthium
found in only a few other angiosperm families. The study of this family is known as synantherology
.
In addition, the name daisy is derived from its Old English meaning, dægesege, from dæges eage meaning "day's eye," and this was because the petals open at dawn and close at dusk.
, eastern Brazil
, the Andes
, the Mediterranean, southern Africa
, central Asia
, and southwestern China).
botanist Paul Dietrich Giseke
. Traditionally two subfamilies were recognised: Asteroideae
(or Tubuliflorae) and Cichorioideae
(or Liguliflorae). The latter has been shown to be extensively paraphyletic, and has now been divided into 11 subfamilies, but the former still stands. The phylogenetic tree
presented below is based on Panero & Funk (2002). The diamond denotes a very poorly supported node
(<50% bootstrap support), the dot a poorly supported node (<80%).
It is noteworthy that the four subfamilies Asteroideae
, Cichorioideae
, Carduoideae
and Mutisioideae
comprise 99% of the specific diversity of the whole family (approximately 70%, 14%, 11% and 3% respectively).
Because of the morphological
complexity exhibited by this family, agreeing on generic circumscriptions has often been difficult for Asteraceae taxonomists. As a result several of these genera have required multiple revisions.
aceous plants, but some shrubs, tree
s and climber
s do exist. Daisies are generally easy to distinguish from other plants, mainly because of their characteristic inflorescence
and many shared apomorphies. However, many closely related species in this family are notoriously difficult to identify to the species level (see "damned yellow composite
" for example).
s, and sometimes fibrous. Stems are generally erect, but sometimes prostrate to ascending. Some species have underground stems in the form of caudices
or rhizome
s, these can be fleshy or woody depending on the species.
and the stems very often contain secretory canals with resin
or latex
(particularly common among the Cichorioideae). The leaves can be alternate
, opposite
, or whorled
. They may be simple, but are often deeply lobed or otherwise incised, often conduplicate or revolute. The margins can be entire or dentate.
The most evident characteristic of Asteraceae is perhaps their inflorescence
: a specialised capitulum
, technically called a calathid or calathidium, but generally referred to as flower head or, alternatively, simply capitulum. The capitulum is a contracted raceme
composed of numerous individual sessile
flower
s, called the florets, all sharing the same receptacle.
The capitulum of Asteraceae has evolved many characteristics that make it look superficially like a single flower. This type of flower-like inflorescence is fairly widespread amongst angiosperms, and has been given the name of pseudanthia
.
Many bract
s form an involucre under the basis of the capitulum; these are called "phyllaries", or "involucral bracts". They may simulate the sepal
s of the pseudanthium. These are mostly herbaceous but can also be brightly coloured (e.g. Helichrysum) or have a scarious texture. The bracts 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 itself be subtended by a bract, called a "palea" or "receptacular bract". These bracts as a group 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 petal
s fused at the base to form a 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 petal
s form the ligule, with the other two petals being inconspicuously small. The Cichorioidea 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, it is always modified into a 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 five stamen
s. The filaments are fused to the corolla, while the anthers are generally 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, expelled with a sort of pump mechanism (nüdelspritze) or a brush.
The pistil is made of two connate carpels. The style has two lobes; stigmatic tissue may be located in the interior surface or form two lateral lines. The ovary
is inferior and has only one ovule
, with basal placentation
.
-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. 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
is often used to help determine plant relationships at the genus and species level. The mature seed
s usually have little endosperm
or none.
. 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 terpenoid
essential oils which never contain iridoid
s.
It is still unknown whether the precise cause of their great success was the development of the highly specialised capitulum
, their ability to store energy as fructan
s (mainly inulin
), which is an advantage in relatively dry zones, or some combination of these and possibly other factors.
Asteraceae are especially common in open and dry environments.
Many members of the Asteraceae are pollinated
by insects, which explains their value in attracting beneficial insects
, but anemophyly
is also present (e.g. Ambrosia
, Artemisia). There are many apomictic
species in the family.
Seeds are ordinarily dispersed intact with the fruiting body, the cypsela. Wind dispersal is common (anemochory) assisted by a hairy pappus. Another common variation is epizoochory, in which the dispersal unit, a single cypsela (e.g. Bidens
) or entire capitulum (e.g. Arctium) provided with hooks, spines or some equivalent structure, sticks to the fur or plumage of an animal (or even to clothes, like in the photo) just to fall off later far from its mother plant.
Commercially important plants in the Asteraceae include the food crops Lactuca sativa (lettuce), Cichorium
(chicory), Cynara scolymus (globe artichoke), Helianthus annuus (sunflower), Smallanthus sonchifolius (yacón), Carthamus tinctorius (safflower) and Helianthus tuberosus (Jerusalem artichoke).
Many members of the family are grown as ornamental plants for their flowers and some are important ornamental crops for the cut flower industry. Some examples are Chrysanthemum
, Gerbera
, Calendula
, Dendranthema, Argyranthemum
, Dahlia
, Tagetes
, Zinnia
and many others.
Other commercially important species include Compositae used as herbs and in herbal teas and other beverages. Chamomile, which comes from two different species, the annual Matricaria recutita or German chamomile, and the perennial Chamaemelum nobile, also called Roman chamomile. Calendula
, also called the pot marigold is grown commercially for herbal teas and the potpourri industry. Echinacea (Echinacea purpurea
), used as a medicinal tea. Winter tarragon, also called Mexican mint marigold, Tagetes lucida
is commonly grown and used as a tarragon substitute in climates where tarragon will not survive. Finally, the wormwood genus Artemisia includes absinthe
(A. absinthium) and tarragon
(A. dracunculus).
Compositae has also been used for industral purposes. Common in all commercial poultry feed, marigold (Tagetes patula) is grown primarily in Mexico and central American nations. Marigold oil, extracted from Tagetes minuta
is used in the cola and cigarette industries.
Plants in Asteraceae are medically important in areas that don't have access to Western medicine. They are also commonly featured in medical and phytochemical journals because the sesquiterpene
lactone
compounds contained within them are an important cause of allergic contact dermatitis
. Allergy to these compounds is the leading cause of allergic contact dermatitis in florists in the US. Pollen
from ragweed Ambrosia
is among the main causes of so called hay fever
in the United States.
Many members of Asteraceae are copious nectar
producers and are useful for evaluating pollinator
populations during their bloom. Centaurea
(knapweed), Helianthus annuus (domestic sunflower), and some species of Solidago (goldenrod) are major "honey
plants" for beekeeper
s. Solidago produces relatively high protein pollen
, which helps honey bee
s overwinter.
Some members of the Asteraceae are economically important as weeds. Notable in the United States are the ragwort, Senecio jacobaea, groundsel Senecio vulgaris and Taraxacum
(dandelion).
The genera Tanacetum
, Chrysanthemum
and Pulicaria
contain species with insecticidal properties.
Parthenium argentatum (guayule) is a source of hypoallergenic
latex
.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of vascular plant
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies. Along with the Orchidaceae
Orchidaceae
The Orchidaceae, commonly referred to as the orchid family, is a morphologically diverse and widespread family of monocots in the order Asparagales. Along with the Asteraceae, it is one of the two largest families of flowering plants, with between 21,950 and 26,049 currently accepted species,...
, this makes it one of the two largest flowering plant families in the world. However, selecting which of the two families is larger has yet to be been done conclusively, owing to the uncertainty around exactly how many species are in each group. The largest composite genera are Senecio
Senecio
Senecio is a genus of the daisy family that includes ragworts and groundsels. The flower heads are normally rayed, completely yellow, and the heads are borne in branched clusters...
(1,000 species), Vernonia
Vernonia
Vernonia is a genus of about 1000 species of forbs and shrubs in the family Asteraceae. Some species are known as Ironweed. Some species are edible and of economic value. They are known for having intense purple flowers. The genus is named for English botanist William Vernon. There are numerous...
(1,000 species), Centaurea
Centaurea
Centaurea is a genus of between 350 and 600 species of herbaceous thistle-like flowering plants in the family Asteraceae. Members of the genus are found only north of the equator, mostly in the Eastern Hemisphere; the Middle East and surrounding regions are particularly species-rich...
(700 species), Cousinia
Cousinia
The genus Cousinia of the tribe Cardueae is in its current circumscription one ofthe larger genera in the Asteraceae, with approximately 600-700 species distributed in central and western Asia....
(600 species), Helichrysum (550 species), and Artemesia
Artemisia (plant)
Artemisia is a large, diverse genus of plants with between 200 to 400 species belonging to the daisy family Asteraceae. It comprises hardy herbs and shrubs known for their volatile oils. They grow in temperate climates of the Northern Hemisphere and Southern Hemisphere, usually in dry or semi-dry...
(550 species).
Most members of Asteraceae are herbaceous, but a significant number are also shrubs, vines and trees. The family is distributed throughout the world, and is most common in the arid
Arid
A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...
and semi-arid regions of subtropical and lower temperate latitudes.
Many economically important products come from composites, including cooking oil
Cooking oil
Cooking oil is purified fat of plant origin, which is usually liquid at room temperature ....
s, lettuce
Lettuce
Lettuce is a temperate annual or biennial plant of the daisy family Asteraceae. It is most often grown as a leaf vegetable. It is eaten either raw, notably in salads, sandwiches, hamburgers, tacos, and many other dishes, or cooked, as in Chinese cuisine in which the stem becomes just as important...
, sunflower seed
Sunflower seed
The sunflower seed is the fruit of the sunflower . The term "sunflower seed" is actually a misnomer when applied to the seed in its pericarp . Botanically speaking, it is more properly referred to as an achene. When dehulled, the edible remainder is called the sunflower kernel.There are three types...
s, artichoke
Artichoke
-Plants:* Globe artichoke, a partially edible perennial thistle originating in southern Europe around the Mediterranean* Jerusalem artichoke, a species of sunflower with an edible tuber...
s, sweetening agents, and tea
Tea
Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...
s. Several genera are also very popular with the horticultural
Horticulture
Horticulture is the industry and science of plant cultivation including the process of preparing soil for the planting of seeds, tubers, or cuttings. Horticulturists work and conduct research in the disciplines of plant propagation and cultivation, crop production, plant breeding and genetic...
community, these include marigolds, chrysanthemum
Chrysanthemum
Chrysanthemums, often called mums or chrysanths, are of the genus constituting approximately 30 species of perennial flowering plants in the family Asteraceae which is native to Asia and northeastern Europe.-Etymology:...
s, dahlia
Dahlia
Dahlia is a genus of bushy, tuberous, perennial plants native to Mexico, Central America, and Colombia. There are at least 36 species of dahlia, some like D. imperialis up to 10 metres tall. Dahlia hybrids are commonly grown as garden plants...
s, zinnia
Zinnia
Zinnia is a genus of 20 species of annual and perennial plants of family Asteraceae, originally from scrub and dry grassland in an area stretching from the American Southwest to South America, but primarily Mexico, and notable for their solitary long-stemmed flowers that come in a variety of bright...
s, and helenium
Helenium
Helenium is a genus of about 40 herbaceous flowering plants in the daisy family Asteraceae, native to North America and Central America. They bear yellow or orange daisy-like flowers...
s.
Etymology
The Latin name 'Asteraceae' is derived from the type genus Aster, which is a Greek term, meaning "star". While 'Compositae', an older but still valid name, means composite and refers to the characteristic inflorescenceInflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
, a special type of pseudanthium
Pseudanthium
A pseudanthium or flower head is a special type of inflorescence, in which several flowers are grouped together to form a flower-like structure. The real flowers are generally small and greatly reduced, but can sometimes be quite large...
found in only a few other angiosperm families. The study of this family is known as synantherology
Synantherology
Synantherology is the study of the plant family Asteraceae . The name of the field refers to the fused anthers possessed by members of the family, and recalls an old French name, synantherées, for the family....
.
In addition, the name daisy is derived from its Old English meaning, dægesege, from dæges eage meaning "day's eye," and this was because the petals open at dawn and close at dusk.
Distribution
Daisies have a worldwide distribution, being found everywhere except Antarctica and the extreme Arctic. They are especially numerous in tropical and subtropical regions (notably Central AmericaCentral America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
, eastern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, the Andes
Andes
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...
, the Mediterranean, southern Africa
Southern Africa
Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English.-UN...
, central Asia
Central Asia
Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...
, and southwestern China).
Taxonomy
Compositae were first described in 1792 by the GermanGermans
The Germans are a Germanic ethnic group native to Central Europe. The English term Germans has referred to the German-speaking population of the Holy Roman Empire since the Late Middle Ages....
botanist Paul Dietrich Giseke
Paul Dietrich Giseke
Paul Dietrich Giseke , was a German botanist, physician, teacher and librarian.Giseke started his studies at the Academic Gymnasium in Hamburg. He joined the University of Göttingen in 1764 and graduated in 1767...
. Traditionally two subfamilies were recognised: Asteroideae
Asteroideae
Asteroideae is a subfamily of the plant family Asteraceae. It contains about 70% of the species of the family.It is made of several tribes including Astereae, Calenduleae, Eupatorieae, Gnaphalieae, Heliantheae, Senecioneae and Tageteae.- Classification :...
(or Tubuliflorae) and Cichorioideae
Cichorioideae
Cichorioideae is a subfamily of the family Asteraceae of flowering plants. Familiar members of Cichorioideae include lettuce, dandelions and Gazanias. The subfamily comprises about 240 genera and about 2900 species...
(or Liguliflorae). The latter has been shown to be extensively paraphyletic, and has now been divided into 11 subfamilies, but the former still stands. The phylogenetic tree
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...
presented below is based on Panero & Funk (2002). The diamond denotes a very poorly supported node
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
(<50% bootstrap support), the dot a poorly supported node (<80%).
It is noteworthy that the four subfamilies Asteroideae
Asteroideae
Asteroideae is a subfamily of the plant family Asteraceae. It contains about 70% of the species of the family.It is made of several tribes including Astereae, Calenduleae, Eupatorieae, Gnaphalieae, Heliantheae, Senecioneae and Tageteae.- Classification :...
, Cichorioideae
Cichorioideae
Cichorioideae is a subfamily of the family Asteraceae of flowering plants. Familiar members of Cichorioideae include lettuce, dandelions and Gazanias. The subfamily comprises about 240 genera and about 2900 species...
, Carduoideae
Carduoideae
Carduoideae is the thistle subfamily of the Asteraceae, or sunflower family, of flowering plants. It comprises a number of tribes in various circumscriptions of the family, in addition to the Cynareae....
and Mutisioideae
Mutisioideae
Mutisioideae is a subfamily of flowering plants in the sunflower family, Asteraceae.-Taxonomy:The subfamily Mutisioideae consists of 3 tribes, 45 genus and about 630 species Tribe Mutisieae* Adenocaulon Hook....
comprise 99% of the specific diversity of the whole family (approximately 70%, 14%, 11% and 3% respectively).
Because of the morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
complexity exhibited by this family, agreeing on generic circumscriptions has often been difficult for Asteraceae taxonomists. As a result several of these genera have required multiple revisions.
Characteristics
Asteraceae are mostly herbHerb
Except in botanical usage, an herb is "any plant with leaves, seeds, or flowers used for flavoring, food, medicine, or perfume" or "a part of such a plant as used in cooking"...
aceous plants, but some shrubs, tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s and climber
Vine
A vine in the narrowest sense is the grapevine , but more generally it can refer to any plant with a growth habit of trailing or scandent, that is to say climbing, stems or runners...
s do exist. Daisies are generally easy to distinguish from other plants, mainly because of their characteristic inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
and many shared apomorphies. However, many closely related species in this family are notoriously difficult to identify to the species level (see "damned yellow composite
Damned yellow composite
A damned or damn yellow composite is a jocular reference to the difficulty of distinguishing many of the numerous species of composite that have yellow flowers and can be difficult to tell apart in the field. It is sometimes reserved for those yellow composites of no particular interest...
" for example).
Roots and stems
Daisy roots are usually taprootTaproot
A taproot is an enlarged, somewhat straight to tapering plant root that grows vertically downward. It forms a center from which other roots sprout laterally.Plants with taproots are difficult to transplant...
s, and sometimes fibrous. Stems are generally erect, but sometimes prostrate to ascending. Some species have underground stems in the form of caudices
Caudex
A caudex is a form of stem morphology appearing as a thickened, short, perennial stem that is either underground or near ground level . It may be swollen for the purpose of water storage, especially in xerophytes...
or rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
s, these can be fleshy or woody depending on the species.
Leaves
The leavesLeaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
and the stems very often contain secretory canals with resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
or latex
Latex
Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...
(particularly common among the Cichorioideae). The leaves can be alternate
Phyllotaxis
In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem .- Pattern structure :...
, opposite
Phyllotaxis
In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem .- Pattern structure :...
, or whorled
Phyllotaxis
In botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem .- Pattern structure :...
. They may be simple, but are often deeply lobed or otherwise incised, often conduplicate or revolute. The margins can be entire or dentate.
Flowers
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
: a specialised capitulum
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
, technically called a calathid or calathidium, but generally referred to as flower head or, alternatively, simply capitulum. The capitulum is a contracted raceme
Raceme
A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...
composed of numerous individual sessile
Sessility (botany)
In botany, sessility is a characteristic of plants whose flowers or leaves are borne directly from the stem or peduncle, and thus lack a petiole or pedicel...
flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s, called the florets, all sharing the same receptacle.
The capitulum of Asteraceae has evolved many characteristics that make it look superficially like a single flower. This type of flower-like inflorescence is fairly widespread amongst angiosperms, and has been given the name of pseudanthia
Pseudanthium
A pseudanthium or flower head is a special type of inflorescence, in which several flowers are grouped together to form a flower-like structure. The real flowers are generally small and greatly reduced, but can sometimes be quite large...
.
Many bract
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
s form an involucre under the basis of the capitulum; these are called "phyllaries", or "involucral bracts". They may simulate the sepal
Sepal
A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...
s of the pseudanthium. These are mostly herbaceous but can also be brightly coloured (e.g. Helichrysum) or have a scarious texture. The bracts 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 itself be subtended by a bract, called a "palea" or "receptacular bract". These bracts as a group are often called "chaff
Chaff
Chaff is the dry, scaly protective casings of the seeds of cereal grain, or similar fine, dry, scaly plant material such as scaly parts of flowers, or finely chopped straw...
". 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 petal
Petal
Petals are modified leaves that surround the reproductive parts of flowers. They often are brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are usually accompanied by another set of special leaves called sepals lying...
s fused at the base to form a 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 petal
Petal
Petals are modified leaves that surround the reproductive parts of flowers. They often are brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are usually accompanied by another set of special leaves called sepals lying...
s form the ligule, with the other two petals being inconspicuously small. The Cichorioidea 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, it is always modified into a pappus
Pappus (flower structure)
The pappus is the modified calyx, the part of an individual disk, ray or ligule floret surrounding the base of the corolla, in flower heads of the plant family Asteraceae. The pappus may be composed of bristles , awns, scales, or may be absent. In some species, the pappus is too small to see...
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 five stamen
Stamen
The stamen is the pollen producing reproductive organ of a flower...
s. The filaments are fused to the corolla, while the anthers are generally connate
Connation
Connation in plants is the developmental fusion of organs of the same type, for example, petals to one another to form a tubular corolla. This is in contrast to adnation, the fusion of dissimilar organs.-Terms for connation of flower parts:...
(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, expelled with a sort of pump mechanism (nüdelspritze) or a brush.
The pistil is made of two connate carpels. The style has two lobes; stigmatic tissue may be located in the interior surface or form two lateral lines. The ovary
Ovary (plants)
In the flowering plants, an ovary is a part of the female reproductive organ of the flower or gynoecium. Specifically, it is the part of the pistil which holds the ovule and is located above or below or at the point of connection with the base of the petals and sepals...
is inferior and has only one ovule
Ovule
Ovule means "small egg". In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: The integument forming its outer layer, the nucellus , and the megaspore-derived female gametophyte in its center...
, with basal placentation
Placentation
In biology, placentation refers to the formation, type and structure, or arrangement of placentas. The function of placentation is to transfer nutrients from maternal tissue to a growing embryo...
.
Fruits and seeds
The fruit of the Asteraceae is acheneAchene
An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...
-like, and is called a cypsela (plural cypselae). Although there are two fused carpels, there is only one locule, and only one seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
per fruit is formed. 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
Helianthus
Helianthus L. is a genus of plants comprising 52 species in the Asteraceae family, all of which are native to North America, with some species Helianthus L. is a genus of plants comprising 52 species in the Asteraceae family, all of which are native to North America, with some species Helianthus...
). Cypsela morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
is often used to help determine plant relationships at the genus and species level. The mature seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s usually have little endosperm
Endosperm
Endosperm is the tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This makes endosperm an important source of nutrition in human diet...
or none.
Metabolites
Asteraceae generally store energy in the form of inulinInulin
Inulins are a group of naturally occurring polysaccharides produced by many types of plants. They belong to a class of fibers known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes...
. They produce iso/chlorogenic acid
Chlorogenic acid
Chlorogenic acid is a hydroxycinnamic acid, a member of a family of naturally occurring organic compounds. These are esters of polyphenolic caffeic acid and cyclitol -quinic acid. It is an important biosynthetic intermediate. It also is one of the phenols found in coffee, bamboo Phyllostachys...
, sesquiterpene
Sesquiterpene
Sesquiterpenes are a class of terpenes that consist of three isoprene units and have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be acyclic or contain rings, including many unique combinations...
lactones, pentacyclic triterpene alcohols, various alkaloid
Alkaloid
Alkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...
s, acetylene
Acetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
s (cyclic, aromatic, with vinyl end groups), tannin
Tannin
A tannin is an astringent, bitter plant polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids.The term tannin refers to the use of...
s. They have terpenoid
Terpene
Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium. They are often strong smelling and thus may have had a protective...
essential oils which never contain iridoid
Iridoid
Iridoids are a class of secondary metabolites found in a wide variety of plants and in some animals. They are monoterpenes biosynthesized from isoprene and they are often intermediates in the biosynthesis of alkaloids. Chemically, the iridoids usually consist of a cyclopentane ring fused to a...
s.
Evolution
Diversification of Asteraceae appears to have taken place roughly 42-36 million years ago, the stem group perhaps being up to 49 million years old.It is still unknown whether the precise cause of their great success was the development of the highly specialised capitulum
Capitulum
The term Capitulum can refer to several things:*In botany, a type of flower head where the bracts are located under the basis, such as a daisy's*Also in botany, the top of a Sphagnum moss plant with compact clusters of young branches....
, their ability to store energy as fructan
Fructan
A fructan is a polymer of fructose molecules. Fructans with a short chain length are known as fructooligosaccharides, whereas longer chain fructans are termed inulins...
s (mainly inulin
Inulin
Inulins are a group of naturally occurring polysaccharides produced by many types of plants. They belong to a class of fibers known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes...
), which is an advantage in relatively dry zones, or some combination of these and possibly other factors.
Ecology
Many members of the Asteraceae are pollinated
Pollination
Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...
by insects, which explains their value in attracting beneficial insects
Beneficial insects
Beneficial insects are any of a number of species of insects that perform valued services like pollination and pest control. The concept of beneficial is subjective and only arises in light of desired outcomes from a human perspective...
, but anemophyly
Pollination syndrome
Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic or biotic, such as birds, bees, flies, and so forth. These traits include flower shape, size, colour, odour, reward type and amount, nectar...
is also present (e.g. Ambrosia
Ragweed
Ragweeds are flowering plants in the genus Ambrosia in the sunflower family Asteraceae. Common names include bitterweeds and bloodweeds....
, Artemisia). There are many apomictic
Apomixis
In botany, apomixis was defined by Winkler as replacement of the normal sexual reproduction by asexual reproduction, without fertilization. This definition notably does not mention meiosis...
species in the family.
Seeds are ordinarily dispersed intact with the fruiting body, the cypsela. Wind dispersal is common (anemochory) assisted by a hairy pappus. Another common variation is epizoochory, in which the dispersal unit, a single cypsela (e.g. Bidens
Bidens
Bidens is a genus of flowering plants in the family Asteraceae. It contains about 200 species. The common names beggarticks, black jack, bur-marigolds, stickseeds, tickseeds and tickseed sunflowers refer to the achene burrs on the seeds of this genus, most of which are barbed...
) or entire capitulum (e.g. Arctium) provided with hooks, spines or some equivalent structure, sticks to the fur or plumage of an animal (or even to clothes, like in the photo) just to fall off later far from its mother plant.
Uses
Cichorium
Cichorium is a genus of flowering plants in the family Asteraceae. The species are commonly known as chicory or endive – there are two cultivated species, and four to six wild species....
(chicory), Cynara scolymus (globe artichoke), Helianthus annuus (sunflower), Smallanthus sonchifolius (yacón), Carthamus tinctorius (safflower) and Helianthus tuberosus (Jerusalem artichoke).
Many members of the family are grown as ornamental plants for their flowers and some are important ornamental crops for the cut flower industry. Some examples are Chrysanthemum
Chrysanthemum
Chrysanthemums, often called mums or chrysanths, are of the genus constituting approximately 30 species of perennial flowering plants in the family Asteraceae which is native to Asia and northeastern Europe.-Etymology:...
, Gerbera
Gerbera
Gerbera L. is a genus of ornamental plants from the sunflower family . It was named in honour of the German botanist and naturalist Traugott Gerber who travelled extensively in Russia and was a friend of Carolus Linnaeus....
, Calendula
Calendula
Calendula , pot marigold, is a genus of about 12–20 species of annual or perennial herbaceous plants in the daisy family Asteraceae, native to the area from Macaronesia east through the Mediterranean region to Iran...
, Dendranthema, Argyranthemum
Argyranthemum
Argyranthemum is a genus of flowering plants belonging to the family Asteraceae. Members of this genus are sometimes also placed in the genus Chrysanthemum....
, Dahlia
Dahlia
Dahlia is a genus of bushy, tuberous, perennial plants native to Mexico, Central America, and Colombia. There are at least 36 species of dahlia, some like D. imperialis up to 10 metres tall. Dahlia hybrids are commonly grown as garden plants...
, Tagetes
Tagetes
Tagetes is a genus of 56 species of annual and perennial mostly herbaceous plants in the sunflower family . The genus is native to North and South America, but some species have become naturalized around the world. One species, T...
, Zinnia
Zinnia
Zinnia is a genus of 20 species of annual and perennial plants of family Asteraceae, originally from scrub and dry grassland in an area stretching from the American Southwest to South America, but primarily Mexico, and notable for their solitary long-stemmed flowers that come in a variety of bright...
and many others.
Other commercially important species include Compositae used as herbs and in herbal teas and other beverages. Chamomile, which comes from two different species, the annual Matricaria recutita or German chamomile, and the perennial Chamaemelum nobile, also called Roman chamomile. Calendula
Calendula
Calendula , pot marigold, is a genus of about 12–20 species of annual or perennial herbaceous plants in the daisy family Asteraceae, native to the area from Macaronesia east through the Mediterranean region to Iran...
, also called the pot marigold is grown commercially for herbal teas and the potpourri industry. Echinacea (Echinacea purpurea
Echinacea purpurea
Echinacea purpurea is a species of flowering plant in the genus Echinacea. Its cone-shaped flowering heads are usually, but not always purple. It is native to eastern North America and present to some extent in the wild in much of the eastern, southeastern and midwest United States...
), used as a medicinal tea. Winter tarragon, also called Mexican mint marigold, Tagetes lucida
Tagetes lucida
Tagetes lucida is a half-hardy sub-shrub native to Mexico and Central America. It is eaten as an herb and is commonly used as a substitute for tarragon. The leaves have a tarragon-like flavor, with hints of anise...
is commonly grown and used as a tarragon substitute in climates where tarragon will not survive. Finally, the wormwood genus Artemisia includes absinthe
Absinthe
Absinthe is historically described as a distilled, highly alcoholic beverage. It is an anise-flavoured spirit derived from herbs, including the flowers and leaves of the herb Artemisia absinthium, commonly referred to as "grande wormwood", together with green anise and sweet fennel...
(A. absinthium) and tarragon
Tarragon
Tarragon or dragon's-wort is a perennial herb in the family Asteraceae related to wormwood. Corresponding to its species name, a common term for the plant is "dragon herb". It is native to a wide area of the Northern Hemisphere from easternmost Europe across central and eastern Asia to India,...
(A. dracunculus).
Compositae has also been used for industral purposes. Common in all commercial poultry feed, marigold (Tagetes patula) is grown primarily in Mexico and central American nations. Marigold oil, extracted from Tagetes minuta
Tagetes minuta
Tagetes minuta, also known as Stinking Roger or black mint, a tall upright marigold plant from the genus Tagetes with small flowers, and is native to the southern half of South America...
is used in the cola and cigarette industries.
Plants in Asteraceae are medically important in areas that don't have access to Western medicine. They are also commonly featured in medical and phytochemical journals because the sesquiterpene
Sesquiterpene
Sesquiterpenes are a class of terpenes that consist of three isoprene units and have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be acyclic or contain rings, including many unique combinations...
lactone
Lactone
In chemistry, a lactone is a cyclic ester which can be seen as the condensation product of an alcohol group -OH and a carboxylic acid group -COOH in the same molecule...
compounds contained within them are an important cause of allergic contact dermatitis
Allergic contact dermatitis
Allergic contact dermatitis is a form of contact dermatitis that is the manifestation of an allergic response caused by contact with a substance....
. Allergy to these compounds is the leading cause of allergic contact dermatitis in florists in the US. Pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
from ragweed Ambrosia
Ambrosia
In ancient Greek mythology, ambrosia is sometimes the food or drink of the Greek gods , often depicted as conferring ageless immortality upon whoever consumes it...
is among the main causes of so called hay fever
Hay Fever
Hay Fever is a comic play written by Noël Coward in 1924 and first produced in 1925 with Marie Tempest as the first Judith Bliss. Laura Hope Crews played the role in New York...
in the United States.
Many members of Asteraceae are copious nectar
Nectar (plant)
Nectar is a sugar-rich liquid produced by plants. It is produced in glands called nectaries, either within the flowers, in which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide anti-herbivore protection...
producers and are useful for evaluating pollinator
Pollinator
A pollinator is the biotic agent that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain...
populations during their bloom. Centaurea
Centaurea
Centaurea is a genus of between 350 and 600 species of herbaceous thistle-like flowering plants in the family Asteraceae. Members of the genus are found only north of the equator, mostly in the Eastern Hemisphere; the Middle East and surrounding regions are particularly species-rich...
(knapweed), Helianthus annuus (domestic sunflower), and some species of Solidago (goldenrod) are major "honey
Honey
Honey is a sweet food made by bees using nectar from flowers. The variety produced by honey bees is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans...
plants" for beekeeper
Beekeeper
A beekeeper is a person who keeps honey bees for the purposes of securing commodities such as honey, beeswax, pollen, royal jelly; pollinating fruits and vegetables; raising queens and bees for sale to other farmers; and/or for purposes satisfying natural scientific curiosity...
s. Solidago produces relatively high protein pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
, which helps honey bee
Honey bee
Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...
s overwinter.
Some members of the Asteraceae are economically important as weeds. Notable in the United States are the ragwort, Senecio jacobaea, groundsel Senecio vulgaris and Taraxacum
Taraxacum
Taraxacum is a large genus of flowering plants in the family Asteraceae. They are native to Eurasia and North America, and two species, T. officinale and T. erythrospermum, are found as weeds worldwide. Both species are edible in their entirety...
(dandelion).
The genera Tanacetum
Tanacetum
Tanacetum is a genus of about 160 species of flowering plant in the family Asteraceae, native to many regions of the Northern Hemisphere.Common names include Tansy , Costmary , and Feverfew ; several other species are also known as tansies.Tanacetum species...
, Chrysanthemum
Chrysanthemum
Chrysanthemums, often called mums or chrysanths, are of the genus constituting approximately 30 species of perennial flowering plants in the family Asteraceae which is native to Asia and northeastern Europe.-Etymology:...
and Pulicaria
Pulicaria
Pulicaria is a genus of flowering plant in the Asteraceae family.It contains over one hundred species, including:* Pulicaria aromatica* Pulicaria dioscorides* Pulicaria diversifolia* Pulicaria dysenterica* Pulicaria elegans...
contain species with insecticidal properties.
Parthenium argentatum (guayule) is a source of hypoallergenic
Hypoallergenic
Hypoallergenic, meaning "below normal" or "slightly" allergenic, was a term first used in a cosmetics campaign in 1953. It is used to describe items that cause or are claimed to cause fewer allergic reactions...
latex
Latex
Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...
.
External links
- Compositae at The Plant List
- Compositae at The Families of Flowering Plants (DELTA)
- Asteraceae at the Encyclopedia of Life
- Asteraceae at the Angiosperm Phylogeny Website
- Asteraceae at the Tree of Life Web Project
- Asteraceae at the online Flora of North America
- Asteraceae at the online Flora of Pakistan
- Asteraceae at the online Flora of Zimbabwe
- Compositae at the online Flora of Taiwan
- Asteraceae at the online Flora of Western Australia
- Compositae at the online Flora of New Zealand
- The International Composite Alliance (TICA) A worldwide group of composite systematists