A
pseudanthium or
flower head is a special type of
inflorescenceAn 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
flowerA 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
sunflowerSunflower 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 (
AsteraceaeThe 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
capitulumThe 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 officinaleTaraxacum 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
bractIn 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
involucreInvolucre 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
pollinationPollination 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:
- Apiaceae
The 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...
- Araceae
Araceae 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...
- 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...
- Campanulaceae
The 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...
- Centrolepidaceae
Centrolepidaceae 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...
- Cornaceae
Cornaceae 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...
- Cyperaceae
Cyperaceae 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...
- Dipsacaceae
The 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...
- Euphorbiaceae
Euphorbiaceae, 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 cyathiaA cyathium is one of the specialised pseudanthia forming the inflorescence of plants in the genus Euphorbia . A cyathium consists of:...
- Eriocaulaceae
The 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,...
- Hamamelidaceae
The Hamamelidaceae is a family of flowering plants in the order Saxifragales, including 27 genera and about 80-90 species, all shrubs and small trees...
- Moraceae
Moraceae — 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...
- Poaceae
The 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...
- Pontederiaceae
Pontederiaceae 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
- Proteaceae
Proteaceae 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,...
- Rubiaceae
The 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 ,...
- Saururaceae
Saururaceae 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:
- Hydatellaceae
Hydatellaceae 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
- Pandanaceae
Pandanaceae 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...
- Triuridaceae
Triuridaceae 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...
- Phyllanthaceae
Phyllanthaceae 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...