A pseudanthium (; : pseudanthia) is an inflorescence that resembles a flower.
Pseudanthia are characteristic of the daisy and sunflower family (Asteraceae), whose flowers are differentiated into ray flowers and disk flowers, unique to this family. The disk flowers in the center of the pseudanthium 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
In all cases, a pseudanthium 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 may be grouped into types. The first type has units of individual flowers that are recognizable as single flowers even if fused. In the second type, the flowers do not appear as individual units and certain organs like stamens and carpels can not be associated with any individual flowers.
History
The term pseudanthium was originally applied to flowers with stamens in two whorls with the outer whorl opposite the petals (obdiplostemonate) or polyandric flowers; by the early 1900s the term was repurposed by the advocates of the 'pseudanthium theory' which assumed flower evolution originated from a polyaxial instead of a monoaxial configuration.
Related terms
Synorganization
The collection of independent organs into a complex structure is called
synorganization.
Head
Head is an equivalent term for flower head and pseudanthium when used in the botanical sense.
Capitulum
Capitulum (plural
capitula) can be used as an exact synonym for pseudanthium and flower head; however, this use is generally but not always restricted to the family Asteraceae. At least one source defines it as a small flower head.
In addition to its botanical use as a term meaning flower head it is also used to mean the top of the
sphagnum plant.
Calathid
Calathid (plural
calathids or
calathidia) is a very rarely used term. It was defined in the 1966 book,
The genera of flowering plants (Angiospermae), as a specific term for a flower head of a plant in the family Asteraceae.
[ However, on-line botanical glossaries do not define it, and Google Scholar does not link to any significant usage of the term in a botanical sense.
]
Plant families
Pseudanthia occur in 40 plant families including:
-
Adoxaceae — in some Viburnum spp.
-
Apiaceae — pseudanthia are called
-
Araceae — pseudanthia are called spadices
-
Asteraceae — The capitula (singular capitulum) or flower heads, which are collections of different types of flowers, is a pseudanthium.
[ Commonly the capitulum has ray flowers specialized to attract pollinators arranged surrounding disc flowers responsible for sexual reproduction, perianth symmetry can be variable within the family.]
-
Campanulaceae
-
Centrolepidaceae
-
Cornaceae
-
Cyperaceae — In subfamily Mapanioideae,
-
Dipsacaceae
-
Euphorbiaceae — in Euphorbia — pseudanthia are called cyathium,
-
Eriocaulaceae
-
Hamamelidaceae
-
Marcgraviaceae
-
Moraceae
-
Myrtaceae — in Actinodium — the pseudanthia is a head-like structure with fertile flowers in the center and showy ray-like structures along the outside.
-
Nothofagus — in subgenus Lophozonia — a three‐flowered Inflorescence without branches.
-
Nyssaceae — in Davidia
-
Poaceae
-
Pontederiaceae
-
Proteaceae
-
Rubiaceae
-
Saururaceae
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:
==Gallery==
