Frond dimorphism refers to a difference in

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except ...

s between the fertile and sterile

frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...

s. Since ferns, unlike

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, a vast majority of ...

s, bear

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

s on the

leaf A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

blade itself, this may affect the form of the frond itself. In some species of ferns, there is virtually no difference between the fertile and sterile fronds, such as in the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

'' Dryopteris'', other than the mere presence of the sori, or fruit-dots, on the back of the fronds. Some other species, such as '' Polystichum acrostichoides'' (Christmas fern), or some ferns of the genus '' Osmunda'', feature dimorphism on a portion of the frond only. Others, such as some species of '' Blechnum'' and '' Woodwardia'', have fertile fronds that are markedly taller than the sterile. Still others, such as '' Osmunda cinnamomea'' (Cinnamon fern), or plants of the family Onocleaceae, have fertile fronds that are completely different from the sterile. Only members of the '' Onocleaceae'' and '' Blechnaceae'' exhibit a propensity towards dimorphy, while no member of the '' Athyriaceae'' is strongly dimorphic, and only some representatives of the '' Thelypteridaceae'' have evolved the condition, suggesting a possible close relationship between ''Onocleaceae'' and ''Blechnaceae''. Its importance has been disputed - Copeland for example, considered it taxonomically important, whereas Tryon and Tryon and Kramer all stated that the importance can only be judged in relation to other characteristics.

References

{{reflist, refs= {{cite book , url=http://www.cabdirect.org/abstracts/19480300756.html;jsessionid=8AD67CF96D4E4B6DBF3EAB02D93D8C9E?gitCommit=4.13.8-6-g6e31ff9 , title=Genera Filicum-the genera of ferns , year=1947 , publisher=Chronica Botanica , location=

Waltham, Massachusetts Waltham ( ) is a city in Middlesex County, Massachusetts, United States, and was an early center for the labor movement as well as a major contributor to the American Industrial Revolution. The original home of the Boston Manufacturing Company, ...

, USA {{cite book , last1=Tryon , first1=R. M. , last2= Tryon , first2=A. F. , year=1982 , title=Ferns and allied plants with special reference to tropical America , publisher=

Springer Publishing Springer Publishing Company is an American publishing company of academic journals and books, focusing on the fields of nursing, gerontology, psychology, social work, counseling, public health, and rehabilitation (neuropsychology). It was ...

, location=

New York, New York New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...

, USA , isbn= 038790672X {{cite book , title=The families and genera of vascular plants , author=Rohwer, J. G. , editor=Klaus Kubitzki , publisher=

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, USA , year=1990 , display-authors=etal {{cite book , url=https://books.google.com/books?id=KOcA7hx572EC&dq=%22Frond+dimorphism%22&pg=PA33 , title=Pteridology in the New Millennium: NBRI Golden Jubilee Volume in Honour of Professor B.K. Nayar , editor=S. Chandra , editor2=M. Srivastava , publisher=

, location=

, USA , year=1990 , isbn=9781402011283 , pages=33–34 Ferns