pseudanthium
{{short description|Type of inflorescence, clusters of flowers}}
{{redirect|Flower head|the band|Flowerhead}}
A pseudanthium ({{langnf|grc||false flower}}; {{plural form}}: pseudanthia) is an inflorescence that resembles a flower.{{cite book |author=Louis P. Ronse De Craene |url=https://books.google.com/books?id=24p-LgWPA50C&pg=PA23 |title=Floral Diagrams: An Aid to Understanding Flower Morphology and Evolution |publisher=Cambridge University Press |date=4 February 2010 |isbn=978-1-139-48455-8 |page=23}} The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower heads, composite flowers,{{Citation |last=Chester |first=Sharon |year=2016 |title=The Arctic Guide: Wildlife of the Far North |publisher=Princeton University Press |url=https://books.google.com/books?id=yDD9CwAAQBAJ&pg=PA514 |isbn=9781400865963 |postscript=.}}{{rp|514}} or capitula, which are special types of inflorescences{{cite book|last=Hutchinson|first=John|title=The genera of flowering plants (Angiospermae)|url=https://archive.org/details/generaofflowerin0001hutc|url-access=registration|year=1964|location=Oxford|publisher=Clarendon Press|lccn=65000676}} in which anything from a small cluster to hundreds or sometimes thousands of flowers are grouped together to form a single flower-like structure. Pseudanthia take various forms. The real flowers (the florets) are generally small and often greatly reduced, but the pseudanthium itself can sometimes be quite large (as in the heads of some varieties of sunflower).
File:Flower July 2011-2 1 cropped.jpgs, and at the center is a dense pack of individual tiny disc flowers. Because the collection has the overall appearance of a single flower, the collection of flowers in the head of this sunflower is called a pseudanthium or a composite.]]
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{{cite web| title=Senecio vulgaris L.| publisher=Missouri Plants| url=http://www.missouriplants.com/Yellowalt/Senecio_vulgaris_page.html| access-date=2 December 2012| archive-url=https://web.archive.org/web/20120627073613/http://www.missouriplants.com/Yellowalt/Senecio_vulgaris_page.html| archive-date=27 June 2012| url-status=dead}} and Taraxacum officinale lacks disk flowers.{{cite web | title=Taraxacum Officinale| publisher=Florida Data| url=http://www.floridata.com/ref/T/tara_off.cfm| access-date = 2 December 2012}} The individual flowers of a pseudanthium in the family Asteraceae (or Compositae) are commonly called florets.{{cite web |title= calflora Botanical Terms |url= http://www.calflora.net/botanicalnames/botanicalterms.html |access-date = 2012-02-26}} The pseudanthium has a whorl of bracts below the flowers, forming an involucre.
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.{{Cite journal|last1=Sokoloff|first1=Dmitry|last2=Rudall|first2=Paula J.|last3=Remizowa|first3=Margarita|date=2006-10-01|title=Flower-like terminal structures in racemose inflorescences: a tool in morphogenetic and evolutionary research|url=https://academic.oup.com/jxb/article/57/13/3517/476828|journal=Journal of Experimental Botany|language=en|volume=57|issue=13|pages=3517–3530|doi=10.1093/jxb/erl126|pmid=17005921|issn=0022-0957|doi-access=free}}
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.{{cite book |author=Elmar Robbrecht |url=https://books.google.com/books?id=7EglAQAAMAAJ |title=Second International Rubiaceae Conference Proceedings |publisher=National Botanic Garden of Belgium |date=1996 |isbn=978-90-72619-29-7 |page=330}}
Related terms
=Synorganization=
The collection of independent organs into a complex structure is called synorganization.{{cite book |url=https://books.google.com/books?id=UTNjK26KVGYC&pg=PA35 |title=Developmental Genetics of the Flower: Advances in Botanical Research |publisher=Elsevier |date=29 September 2006 |isbn=978-0-08-046463-3 |pages=35–}}
=Head=
Head is an equivalent term for flower head and pseudanthium when used in the botanical sense.{{Citation needed|date=February 2021}}
=Capitulum=
Capitulum (plural capitula) can be used as an exact synonym for pseudanthium and flower head;{{Citation needed|date=February 2021}} however, this use is generally but not always restricted to the family Asteraceae.{{Citation needed|date=February 2021}} At least one source defines it as a small flower head.{{cite book|last=Harris|first=James|title=Plant Identification Terminology An illustrated Glossary|year=2001|publisher=Spring Lake|isbn=978-0-9640221-6-4}} In addition to its botanical use as a term meaning flower head it is also used to mean the top of the sphagnum plant.{{cite web | title = Australian bryophytes | url = http://www.anbg.gov.au/bryophyte/ecology-sphagnum.html | access-date = 2012-02-26 }}
=Calathid=
Calathid (plural calathids or calathidia) is a very rarely used term.{{Citation needed|date=February 2021}} 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,{{When|date=February 2021}} and Google Scholar does not link to any significant usage of the term in a botanical sense.{{When|date=February 2021}}
Plant families
File:Spathiphyllum cochlearispathum RTBG.jpg) pseudanthium]]
Pseudanthia occur in 40 plant families including:{{cite book |author=Karl Esser |url=https://books.google.com/books?id=bHf1CAAAQBAJ&pg=PA83 |title=Progress in Botany: Structural Botany Physiology Genetics Taxonomy Geobotany |publisher=Springer Science & Business Media |date=6 December 2012 |isbn=978-3-642-78020-2 |page=83}}
- Adoxaceae — in some Viburnum spp.
- Apiaceae — pseudanthia are called umbels
- Araceae — pseudanthia are called spadices
- Asteraceae — The capitula (singular capitulum) or flower heads, which are collections of different types of flowers, is a pseudanthium.{{cite book |url=https://books.google.com/books?id=EkI-AwAAQBAJ&pg=PA299 |title=The Molecular Genetics of Floral Transition and Flower Development |publisher=Elsevier Science |date=16 June 2014 |isbn=978-0-12-417181-7 |page=299}} The individual flowers of a capitulum are called florets. 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.{{Cite journal|last1=Bello|first1=M. Angélica|last2=Álvarez|first2=Ines|last3=Torices|first3=Rubén|last4=Fuertes-Aguilar|first4=Javier|date=2013|title=Floral development and evolution of capitulum structure in Anacyclus (Anthemideae, Asteraceae)|journal=Annals of Botany|volume=112|issue=8|pages=1597–1612|doi=10.1093/aob/mcs301|jstor=42801622|pmid=23287557|pmc=3828941|issn=0305-7364}}
- Campanulaceae{{cite book |author=Rolf H. J. Schlegel |url=https://books.google.com/books?id=LjLvDwAAQBAJ&pg=PP459 |title=Dictionary of Plant Breeding |publisher=CRC Press |date=22 July 2020 |isbn=978-1-00-006698-2 |page=459}}
- Centrolepidaceae — Where individual male and female flowers are grouped together and wrapped in bracts forming a pseudanthium appearing as a bisexual flower.{{cite book|author=Gwen Jean Harden |url=https://books.google.com/books?id=BZXDWrUebgwC&pg=PA407 |title=Flora of New South Wales |publisher=UNSW Press |date=1990 |isbn=978-0-86840-188-1 |page=407}}
- Cornaceae
File:Lepiro articu 090825-12420 ith.JPG]]
- Cyperaceae — In subfamily Mapanioideae,{{Cite web|title=Cyperaceae - Evolution and classification|url=https://www.britannica.com/plant/Cyperaceae|access-date=2021-02-14|website=Encyclopedia Britannica|language=en}} pseudanthia are termed spicoids.{{Cite journal|last1=Simpson|first1=David A.|last2=Furness|first2=Carol A.|last3=Hodkinson|first3=Trevor R.|last4=Muasya|first4=A. Muthama|last5=Chase|first5=Mark W.|date=July 2003|title=Phylogenetic relationships in Cyperaceae subfamily Mapanioideae inferred from pollen and plastid DNA sequence data|url=https://pubmed.ncbi.nlm.nih.gov/21659207/|journal=American Journal of Botany|volume=90|issue=7|pages=1071–1086|doi=10.3732/ajb.90.7.1071|issn=0002-9122|pmid=21659207|bibcode=2003AmJB...90.1071S }} In Lepironia sp the pseudanthium is greatly condensed with staminate flowers surrounding a central terminal pistillate female flower.{{Cite journal|last1=Prychid|first1=C. J.|last2=Bruhl|first2=J. J.|date=2013|title=Floral ontogeny and gene protein localization rules out euanthial interpretation of reproductive units in Lepironia (Cyperaceae, Mapanioideae, Chrysitricheae)|journal=Annals of Botany|volume=112|issue=1|pages=161–177|doi=10.1093/aob/mct111|jstor=42801396|pmid=23723258|pmc=3690996|issn=0305-7364}}
- Dipsacaceae
- Euphorbiaceae — in Euphorbia — pseudanthia are called cyathia,{{cite book |url=https://books.google.com/books?id=nybRCwAAQBAJ&pg=PA176 |title=Plant Ecology in the Middle East |publisher=OUP Oxford |date=14 January 2016 |isbn=978-0-19-107873-6 |page=176}} composed of a single carpal flower with few to many single-stamen staminate flowers contained within a cup-shaped structure or bracts; the bracts are often rimmed with nectaries and less commonly petal-like structures.{{cite book |author=James L. Castner |url=https://books.google.com/books?id=uSpFAQAAIAAJ |title=Photographic Atlas of Botany and Guide to Plant Identification |publisher=Feline Press |date=2004 |isbn=978-0-9625150-0-2 |page=145}} The central cyathia may be composed of all male flowers.{{cite book |author=Chittaranjan Kole |url=https://books.google.com/books?id=UdDMCfgr4dEC&pg=PA125 |title=Wild Crop Relatives: Genomic and Breeding Resources: Plantation and Ornamental Crops |publisher=Springer Science & Business Media |date=1 September 2011 |isbn=978-3-642-21201-7 |page=125}}
File:Euphorbia caput-medusae 01.JPG
File:Actinodium cunninghamii - Flickr - Kevin Thiele.jpg
- Myrtaceae — in Actinodium — the pseudanthia is a head-like structure with fertile flowers in the center and showy ray-like structures along the outside.{{Cite journal|last1=Claßen-Bockhoff|first1=Regine|last2=Ruonala|first2=Raili|last3=Bull-Hereñu|first3=Kester|last4=Marchant|first4=Neville|last5=Albert|first5=Victor A.|date=2013-03-01|title=The unique pseudanthium of Actinodium (Myrtaceae) - morphological reinvestigation and possible regulation by CYCLOIDEA -like genes|url= |journal=EvoDevo|volume=4|issue=1|pages=8|doi=10.1186/2041-9139-4-8|issn=2041-9139|pmc=3610234|pmid=23448118 |doi-access=free }}
- Nothofagaceae — in subgenus Lophozonia — a three‐flowered dichasium without branches.{{Cite journal|last1=Rozefelds|first1=Andrew C.|last2=Drinnan|first2=Andrew N.|date=1998|title=Ontogeny and Diversity in Staminate Flowers of Nothofagus (Nothofagaceae)|url=https://www.jstor.org/stable/10.1086/314090|journal=International Journal of Plant Sciences|volume=159|issue=6|pages=906–922|doi=10.1086/314090|jstor=10.1086/314090|bibcode=1998IJPlS.159..906R |s2cid=83956542|issn=1058-5893|url-access=subscription}}
- Nyssaceae — in Davidia{{cite journal |author1=Claßen-Bockhoff, R. |author2=Arndt, M. |title=Flower-like heads from flower-like meristems: pseudanthium development in Davidia involucrata (Nyssaceae) |journal=J Plant Res |volume=131 |pages=443–458 |date=2018 |issue=3 |doi=10.1007/s10265-018-1029-6|pmid=29569169 |bibcode=2018JPlR..131..443C |s2cid=4202581 }}
- 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).{{Citation needed|date=February 2021}} Possible pseudanthia of this type may occur in the following families:
- Araceae — in subfamily Lemnoideae
- Hydatellaceae
- Pandanaceae
- PhyllanthaceaePetra Hoffmann, Hashendra S. Kathriarachchi, and Kenneth J. Wurdack. 2006. "A Phylogenetic Classification of Phyllanthaceae (Malpighiales)." Kew Bulletin. 61(1):40.
- Triuridaceae{{Cite journal|last=Rudall|first=Paula J.|date=2003|title=Monocot Pseudanthia Revisited: Floral Structure of the Mycoheterotrophic Family Triuridaceae|url=https://www.jstor.org/stable/10.1086/376879|journal=International Journal of Plant Sciences|volume=164|issue=S5|pages=S307–S320|doi=10.1086/376879|jstor=10.1086/376879|bibcode=2003IJPlS.164S.307R |s2cid=85115689|issn=1058-5893|url-access=subscription}}
Gallery
File:Ubor hoofdie.svg|Diagram of a flower head. Note bracts surrounding the flowers, which would be absent on a capitulum.
File:Bellis perennis white (aka).jpg|Flower head of a common daisy (Bellis perennis)
File:Flower head.jpg|Flowers open in succession in head of a sunflower (Helianthus annuus), with ray florets forming the 'petals'
File:Hieracium 2007-1.jpg|Close up of the ray corolla of Hieracium lachenalii; every "petal" is actually a separate five-petaled flower complete with its own stamens and making its own fruit.
File:EricameriaNauseosa 8691.JPG|Discoid (having only disk flowers) flower heads of Ericameria nauseosa (rubber rabbitbrush)
File:Senecio_angulatus_kz11.jpg|Flower head of creeping groundsel (Senecio angulatus) with petaloid ray florets and tubular disc florets in the middle