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Pseudanthium

Type of inflorescence, clusters of flowers

Type of inflorescence, clusters of flowers

A pseudanthium (; : pseudanthia) is an inflorescence that resembles a flower. 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, or capitula, which are special types of inflorescences 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).

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 and Taraxacum officinale lacks disk flowers. The individual flowers of a pseudanthium in the family Asteraceae (or Compositae) are commonly called florets. 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.

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.

Plant families

Pseudanthia occur in 40 plant families including:

  • 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. The individual flowers of a capitulum are called florets.
  • Campanulaceae
  • Centrolepidaceae — Where individual male and female flowers are grouped together and wrapped in bracts forming a pseudanthium appearing as a bisexual flower.
  • Cornaceae
  • Cyperaceae — In subfamily Mapanioideae, pseudanthia are termed spicoids. In Lepironia sp the pseudanthium is greatly condensed with staminate flowers surrounding a central terminal pistillate female flower.
  • Dipsacaceae
  • Euphorbiaceae — in Euphorbia — pseudanthia are called cyathia, 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. The central cyathia may be composed of all male flowers.
Euphorbia caput-medusae 01
  • Eriocaulaceae
  • Hamamelidaceae — in Rhodoleia
  • Marcgraviaceae
  • Moraceae
''Actinodium cunninghamii'' pseudanthia
  • Myrtaceae — in Actinodium — the pseudanthia is a head-like structure with fertile flowers in the center and showy ray-like structures along the outside.
  • Nothofagaceae — in subgenus Lophozonia — a three‐flowered dichasium without branches.
  • Nyssaceae — in Davidia
  • 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:

  • Araceae — in subfamily Lemnoideae
  • Hydatellaceae
  • Pandanaceae
  • Phyllanthaceae
  • Triuridaceae

References

References

  1. Louis P. Ronse De Craene. (4 February 2010). "Floral Diagrams: An Aid to Understanding Flower Morphology and Evolution". Cambridge University Press.
  2. Chester, Sharon. (2016). "The Arctic Guide: Wildlife of the Far North". Princeton University Press.
  3. Hutchinson, John. (1964). "The genera of flowering plants (Angiospermae)". Clarendon Press.
  4. "Senecio vulgaris L.". Missouri Plants.
  5. "Taraxacum Officinale". Florida Data.
  6. "calflora Botanical Terms".
  7. (2006-10-01). "Flower-like terminal structures in racemose inflorescences: a tool in morphogenetic and evolutionary research". Journal of Experimental Botany.
  8. Elmar Robbrecht. (1996). "Second International Rubiaceae Conference Proceedings". National Botanic Garden of Belgium.
  9. (29 September 2006). "Developmental Genetics of the Flower: Advances in Botanical Research". Elsevier.
  10. Harris, James. (2001). "Plant Identification Terminology An illustrated Glossary". Spring Lake.
  11. "Australian bryophytes". link
  12. Karl Esser. (6 December 2012). "Progress in Botany: Structural Botany Physiology Genetics Taxonomy Geobotany". Springer Science & Business Media.
  13. (16 June 2014). "The Molecular Genetics of Floral Transition and Flower Development". Elsevier Science.
  14. (2013). "Floral development and evolution of capitulum structure in Anacyclus (Anthemideae, Asteraceae)". Annals of Botany.
  15. Rolf H. J. Schlegel. (22 July 2020). "Dictionary of Plant Breeding". CRC Press.
  16. Gwen Jean Harden. (1990). "Flora of New South Wales". UNSW Press.
  17. "Cyperaceae - Evolution and classification".
  18. (July 2003). "Phylogenetic relationships in Cyperaceae subfamily Mapanioideae inferred from pollen and plastid DNA sequence data". American Journal of Botany.
  19. (2013). "Floral ontogeny and gene protein localization rules out euanthial interpretation of reproductive units in Lepironia (Cyperaceae, Mapanioideae, Chrysitricheae)". Annals of Botany.
  20. (14 January 2016). "Plant Ecology in the Middle East". OUP Oxford.
  21. James L. Castner. (2004). "Photographic Atlas of Botany and Guide to Plant Identification". Feline Press.
  22. Chittaranjan Kole. (1 September 2011). "Wild Crop Relatives: Genomic and Breeding Resources: Plantation and Ornamental Crops". Springer Science & Business Media.
  23. (2013-03-01). "The unique pseudanthium of Actinodium (Myrtaceae) - morphological reinvestigation and possible regulation by CYCLOIDEA -like genes". EvoDevo.
  24. (1998). "Ontogeny and Diversity in Staminate Flowers of Nothofagus (Nothofagaceae)". International Journal of Plant Sciences.
  25. (2018). "Flower-like heads from flower-like meristems: pseudanthium development in Davidia involucrata (Nyssaceae)". J Plant Res.
  26. Petra Hoffmann, Hashendra S. Kathriarachchi, and Kenneth J. Wurdack. 2006. "A Phylogenetic Classification of Phyllanthaceae (Malpighiales)." ''Kew Bulletin.'' '''61'''(1):40.
  27. Rudall, Paula J.. (2003). "Monocot Pseudanthia Revisited: Floral Structure of the Mycoheterotrophic Family Triuridaceae". International Journal of Plant Sciences.
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