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 t ...

s between the fertile and sterile fronds. Since ferns, unlike

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

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, f ...

s on the

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

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 extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

'' 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 ''Osmundastrum'' is genus of leptosporangiate ferns in the family Osmundaceae with one living species, ''Osmundastrum cinnamomeum'', the cinnamon fern. It is native to the Americas and eastern Asia, growing in swamps, bogs and moist woodlands. I ...

'' (Cinnamon fern), or plants of the family

Onocleaceae Onocleaceae is a small family of terrestrial ferns in the order Polypodiales. It is placed in the suborder Aspleniineae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Alternatively, the family, along with Blechnaceae, may be ...

, have fertile fronds that are completely different from the sterile. Only members of the ''

'' and ''

Blechnaceae Blechnaceae is a family of ferns in the order Polypodiales, with a cosmopolitan distribution. Its status as a family and the number of genera included have both varied considerably. In the Pteridophyte Phylogeny Group classification of 2016 ( ...

'' exhibit a propensity towards dimorphy, while no member of the ''

Athyriaceae The Athyriaceae (ladyferns and allies) are a family of terrestrial ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family is placed in the suborder Aspleniineae, and includes two gene ...

'' is strongly dimorphic, and only some representatives of the ''

Thelypteridaceae Thelypteridaceae is a family of about 900 species of ferns in the order Polypodiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is placed in the suborder Aspleniineae. Alternatively, the family may be submerged in a v ...

'' 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

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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, th ...

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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 es ...

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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 Uni ...

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