Pseudanthium
A pseudanthium (Greek for "false flower") or flower head is a special type of inflorescence[1], 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 (as in the sunflower flower head). Pseudanthia take various forms. The individual flowers of a pseudanthium can be called florets.[2]
Pseudanthia are characteristic of the sunflower family (Asteraceae). Flowers in the asteraceae family are differentiated into ray and disk flowers, which are unique to the 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[3][4] and Taraxacum officinale lacks disk flowers.[5][6] The pseudanthium has a whorl of bracts 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.
Related terms
Head
This is an equivalent term for flower head and pseudanthium when used in the botanical sense.[7][8]
Capitulum (plural capitula)
Capitulum can be used as an exact synonym for pseudanthium and flower head.[9][10][2], however its use is generally but not always restricted to the asteraceae family. At least one source defines it as a small flower head.[11] In addition to its botanical use as a term meaning flower head it is also used to mean the top of the sphagnum plant.[12]
Calathid (plural calathids or calathidia)
This 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 asteraceae family[1]. 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 the following plant families:
- Apiaceae
- Araceae - pseudanthia are called spadix
- Asteraceae
- Campanulaceae
- Centrolepidaceae
- Cornaceae
- Cyperaceae
- Dipsacaceae
- Euphorbiaceae — pseudanthia are called cyathia
- Eriocaulaceae
- Hamamelidaceae
- Moraceae
- Poaceae
- Pontederiaceae — in Hydrothrix
- Proteaceae
- Rubiaceae
- Saururaceae — 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:
Gallery
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Diagram of a flower head. Note bracts surrounding the flowers, which would be absent on a capitulum.
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Flower head of a common daisy (Bellis perennis)
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Flowers open in succession in head of a sunflower (Helianthus annuus), with ray florets forming the 'petals'
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Close up of the ray corolla of a Hieracium lachenalii; every "petal" is actually a separate five-petaled flower complete with its own stamens and making its own fruit.
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Discoid (having only disk flowers) flower heads of a rubber rabbitbrush.
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References
- ^ a b Hutchinson, John (1964). The genera of flowering plants (Angiospermae). Oxford: Clarendon Press. LCCN 65676.
- ^ a b "calflora Botanical Terms". http://www.calflora.net/botanicalnames/botanicalterms.html. Retrieved 2012-02-26.
- ^ http://www.missouriplants.com/Yellowalt/Senecio_vulgaris_page.html
- ^ http://www.cdfa.ca.gov/phpps/IPC/weedinfo/senecio.htm
- ^ http://www.floridata.com/ref/T/tara_off.cfm
- ^ http://www.missouriplants.com/Yellowalt/Taraxacum_erythrospermum_page.html
- ^ "The Jepson Herbarium Glossary". http://ucjeps.berkeley.edu/interchange/JM_glossary.html. Retrieved 2012-02-26.
- ^ "GardenWeb Glossary of Botanical Terms". http://glossary.gardenweb.com/glossary/nph-ind.cgi?scrug=16677&k=head&b=and&r=root&s=both. Retrieved 2012-02-26.
- ^ "Dictionary of Botany Capitulum". http://botanydictionary.org/capitulum.html. Retrieved 2012-02-26.
- ^ "GardenWeb Glossary". http://glossary.gardenweb.com/glossary/nph-ind.cgi?scrug=16677&k=capitulum&b=and&r=root&s=both. Retrieved 2012-02-26.
- ^ Harris, James (2001). Plant Identification Terminology An illustrated Glossary. Spring Lake. ISBN 0-9640221.
- ^ "Australian bryophytes". http://www.anbg.gov.au/bryophyte/ecology-sphagnum.html. Retrieved 2012-02-26.
- ^ Petra Hoffmann, Hashendra S. Kathriarachchi, and Kenneth J. Wurdack. 2006. "A Phylogenetic Classification of Phyllanthaceae (Malpighiales)." Kew Bulletin. 61(1):40.
