Pseudanthium
Encyclopedia
A pseudanthium or flower head is a special type of inflorescence
, in which several flower
s are grouped together to form a flower-like structure. The real flowers are generally small and greatly reduced, but can sometimes be quite large (as in the sunflower
flower-head). Pseudanthia take various forms.
Pseudanthia are characteristic of the sunflower family (Asteraceae
), where they are called calathidia, calathids or capitula. The flowers are differentiated into ray and disk flowers, which are unique to the family. The disk flowers in the center of the pseudanthium (called a flower head or capitulum
in Asteraceae) are actinomorphic and the corolla is fused into a tube. Flowers on the periphery are zygomorphic and the corolla has one large lobe (the so-called "petals" of a daisy are individual ray flowers, for example). Either ray or disk flowers may be absent in some plants: Senecio vulgaris lacks ray flowers and Taraxacum officinale
lacks disk flowers. The capitulum has a whorl of bract
s below the flowers, forming an involucre
.
In all cases, a pseudanthium (inflorescence) is superficially indistinguishable from a flower, but closer inspection of its anatomy will reveal that it is composed of multiple flowers. Thus, the pseudanthium represents an evolutionary convergence of the inflorescence to a reduced reproductive unit that may function in pollination
like a single flower, at least in plants that are animal pollinated.
Pseudanthia occur in the following plant families:
In some families it is not yet clear whether the 'flower' represents a pseudanthium, because the anatomical work has not been done (or is still ambiguous due to considerable evolutionary reduction). Possible pseudanthia of this type may occur in the following families:
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...
, in which several 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 are grouped together to form a flower-like structure. The real flowers are generally small and greatly reduced, but can sometimes be quite large (as in the sunflower
Sunflower
Sunflower is an annual plant native to the Americas. It possesses a large inflorescence . The sunflower got its name from its huge, fiery blooms, whose shape and image is often used to depict the sun. The sunflower has a rough, hairy stem, broad, coarsely toothed, rough leaves and circular heads...
flower-head). Pseudanthia take various forms.
Pseudanthia are characteristic of the sunflower family (Asteraceae
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
), where they are called calathidia, calathids or capitula. The flowers are differentiated into ray and disk flowers, which are unique to the family. The disk flowers in the center of the pseudanthium (called a flower head or 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....
in Asteraceae) are actinomorphic and the corolla is fused into a tube. Flowers on the periphery are zygomorphic and the corolla has one large lobe (the so-called "petals" of a daisy are individual ray flowers, for example). Either ray or disk flowers may be absent in some plants: Senecio vulgaris lacks ray flowers and Taraxacum officinale
Taraxacum officinale
Taraxacum officinale, the common dandelion , is a herbaceous perennial plant of the family Asteraceae . It can be found growing in temperate regions of the world, in lawns, on roadsides, on disturbed banks and shores of water ways, and other areas with moist soils. T...
lacks disk flowers. The capitulum has a whorl of 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 below the flowers, forming an involucre
Involucre
Involucre may refer to* involucral bract, a bract, bract pair, or whorl of bracts surrounding a flower or inflorescence* a term sometimes misused for the cupule surrounding developing nuts in the Fagaceae...
.
In all cases, a pseudanthium (inflorescence) is superficially indistinguishable from a flower, but closer inspection of its anatomy will reveal that it is composed of multiple flowers. Thus, the pseudanthium represents an evolutionary convergence of the inflorescence to a reduced reproductive unit that may function in pollination
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...
like a single flower, at least in plants that are animal pollinated.
Pseudanthia occur in the following plant families:
- ApiaceaeApiaceaeThe Apiaceae , commonly known as carrot or parsley family, is a group of mostly aromatic plants with hollow stems. The family is large, with more than 3,700 species spread across 434 genera, it is the sixteenth largest family of flowering plants...
- AraceaeAraceaeAraceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe or leaf-like bract. Also known as the Arum family, members are often colloquially...
- AsteraceaeAsteraceaeThe Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
- CampanulaceaeCampanulaceaeThe family Campanulaceae , of the order Asterales, contains about 2000 species in 70 genera of herbaceous plants, shrubs, and rarely small trees, often with milky non-toxic sap...
- CentrolepidaceaeCentrolepidaceaeCentrolepidaceae is a botanical name for a family of flowering plants. Such a family has been recognized by most taxonomists.The APG II system, of 2003 , also recognises such a family, and assigns it to the order Poales in the clade commelinids in the monocots.The family is now regarded as...
- CornaceaeCornaceaeCornaceae is a cosmopolitan family of flowering plants in the order Cornales. It contains approximately 110 species, mostly trees and shrubs, which may be deciduous or evergreen. Members of this family usually have opposite or alternate simple leaves, four- or five-parted flowers clustered in...
- CyperaceaeCyperaceaeCyperaceae are a family of monocotyledonous graminoid flowering plants known as sedges, which superficially resemble grasses or rushes. The family is large, with some 5,500 species described in about 109 genera. These species are widely distributed, with the centers of diversity for the group...
- DipsacaceaeDipsacaceaeThe Dipsacaceae, or teasel family, of the order Dipsacales contains 350 species of perennial or biennial herbs and shrubs in eleven genera. Native to most temperate climates, they are found in Europe, Asia and Africa...
- EuphorbiaceaeEuphorbiaceaeEuphorbiaceae, the Spurge family are a large family of flowering plants with 300 genera and around 7,500 species. Most are herbs, but some, especially in the tropics, are also shrubs or trees. Some are succulent and resemble cacti....
— there the pseudanthia are called cyathiaCyathiumA cyathium is one of the specialised pseudanthia forming the inflorescence of plants in the genus Euphorbia . A cyathium consists of:... - EriocaulaceaeEriocaulaceaeThe Eriocaulaceae or pipewort family is a family of monocotyledonous flowering plants in the order Poales. The family is large, with about 1,150-1,200 species described in ten genera. The family is widely distributed, with the centers of diversity for the group occurring in tropical regions,...
- HamamelidaceaeHamamelidaceaeThe Hamamelidaceae is a family of flowering plants in the order Saxifragales, including 27 genera and about 80-90 species, all shrubs and small trees...
- MoraceaeMoraceaeMoraceae — often called the mulberry family or fig family — are a family of flowering plants comprising about 40 genera and over 1000 species. Most are widespread in tropical and subtropical regions, less so in temperate climates...
- PoaceaePoaceaeThe Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...
- PontederiaceaePontederiaceaePontederiaceae is the botanical name of a family of flowering plants.The APG II system, of 2003 places the family in the order Commelinales, in the commelinid clade, in the monocots. It is a small family of heterostylous aquatic plants, occurring in tropical and subtropical waters...
— in Hydrothrix - ProteaceaeProteaceaeProteaceae is a family of flowering plants distributed in the Southern Hemisphere. The family comprises about 80 genera with about 1600 species. Together with the Platanaceae and Nelumbonaceae they make up the order Proteales. Well known genera include Protea, Banksia, Embothrium, Grevillea,...
- RubiaceaeRubiaceaeThe Rubiaceae is a family of flowering plants, variously called the coffee family, madder family, or bedstraw family. The group contains many commonly known plants, including the economically important coffee , quinine , and gambier , and the horticulturally valuable madder , west indian jasmine ,...
- SaururaceaeSaururaceaeSaururaceae is a plant family comprising four genera and seven species of herbaceous flowering plants native to eastern and southern Asia and North America. The family has been recognised by most taxonomists, and is sometimes known as the "lizard's-tail family"...
— in Anemopsis
In some families it is not yet clear whether the 'flower' represents a pseudanthium, because the anatomical work has not been done (or is still ambiguous due to considerable evolutionary reduction). Possible pseudanthia of this type may occur in the following families:
- HydatellaceaeHydatellaceaeHydatellaceae are small, aquatic flowering plants. The family includes the genus Trithuria, which has been recently re-defined to include the genus Hydatella. The family consists of about a dozen species. These tiny , relatively simple, aquatic plants occur in Australasia and India. The simple...
- Lemnaceae
- PandanaceaePandanaceaePandanaceae is a family of flowering plants native to the tropics of the Old World. Such a family has been widely recognized by taxonomists.Pandanaceae are trees or climbing or scrambling shrubs distributed in the Old World tropics and are adapted from sea level in salted beaches to mountain cloud...
- TriuridaceaeTriuridaceaeTriuridaceae is a family of flowering plants. Such a family has been recognized by relatively few taxonomists.The APG II system, of 2003, does recognize such a family and places it in the order Pandanales, in the clade monocots...
- PhyllanthaceaePhyllanthaceaePhyllanthaceae is a family of flowering plants in the eudicot order Malpighiales. It is most closely related to the family Picrodendraceae. The Phyllanthaceae are most numerous in the tropics, with many in the south temperate zone, and a few ranging as far north as the middle of the north temperate...