6.2.2: Ferns
- Page ID
- 35338
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Gametophyte Morphology
Fern gametophytes are reduced, thalloid, and heart-shaped. They are often referred to as a prothallus or prothallium.
![Three fern gametophytes](https://bio.libretexts.org/@api/deki/files/45541/Pter1025_Fern_gametophytes_L.jpg?revision=1&size=bestfit&width=820&height=605)
![A labeled cross section through a fern prothallus](https://bio.libretexts.org/@api/deki/files/29962/InkedFern_Archegonia_underside_LI.jpg?revision=1&size=bestfit&width=967&height=480)
![The underside of a fern prothallus showing rhizoids and many archegonia clustered near the center.](https://bio.libretexts.org/@api/deki/files/29963/InkedFern_Prothallium_only_archegonia_LI.jpg?revision=1&size=bestfit&width=580&height=437)
![A close up of the fern gametophyte, showing an antheridium and an archegonium](https://bio.libretexts.org/@api/deki/files/29964/InkedFern_Archegonium_and_Antheridium_LI.jpg?revision=1&size=bestfit&width=596&height=450)
![Fern gametophytes showing male and female structures and the environmental cues that select for each](https://bio.libretexts.org/@api/deki/files/45542/Environmental_Sex_Determination_Fern_gametophyte.jpg?revision=1&size=bestfit&width=720&height=577)
Sporophyte Morphology
Fern sporophytes are composed of megaphylls, often pinnately compound fronds that emerging as fiddleheads in the spring. Sporangia are produced in clusters called sori (sorus, singular) on the fronds.
![A fern frond emerging from a rhizome](https://bio.libretexts.org/@api/deki/files/29968/InkedBracken_(PSF)_LI.jpg?revision=1)
Circinate Vernation
Circinate vernation is a term used to describe the development of the fern fiddlehead into a frond. Because plants grow apically, it is important to protect the apical meristems in growing organs (as we have seen in both axillary and terminal buds with the evolution of bud scales). The fiddlehead is essentially a structure that tucks away the growing tips of the fronds. As the frond develops, it gradually unfurls, releasing the tips last.
![The fiddlehead of a deer fern frond](https://bio.libretexts.org/@api/deki/files/27322/Fern_fiddlehead_3.jpg?revision=1&size=bestfit&width=469&height=626)
![The fuzzy fiddlehead of a sword fern frond](https://bio.libretexts.org/@api/deki/files/27323/Fern_fiddlehead.jpg?revision=1&size=bestfit&width=467&height=623)
![A five-finger maidenhair fern in the process of circinate vernation](https://bio.libretexts.org/@api/deki/files/27320/Circinate_vernation_fern.jpg?revision=1&size=bestfit&width=550&height=500)
![A five finger maidenhair fern, fully open and mature](https://bio.libretexts.org/@api/deki/files/27321/Five_finger_maidenhair_fern.jpg?revision=1&size=bestfit&width=378&height=504)
Sori
A sorus (plural, sori) is a cluster of sporangia, often protected by an umbrella-like structure called the indusium as the spores mature. Each sporangium is lined by an inflated strip of cells called an annulus. When the spores have matured, the cells in the annulus begin to dry out, causing the cells to collapse and pull the sporangium open, releasing the spores.
![A fern frond where each pinna has two rows of fuzzy-looking orange lumps (sori)](https://bio.libretexts.org/@api/deki/files/29966/Fern_Polypodium_sori_2.jpg?revision=1&size=bestfit&width=515&height=917)
![A labeled cross section through a fern sorus with an indusium](https://bio.libretexts.org/@api/deki/files/29967/InkedFern_(Cyrtomium)_Sorus_2_LI.jpg?revision=1&size=bestfit&width=795&height=600)
![A cross section through a fern sorus with a small leaf](https://bio.libretexts.org/@api/deki/files/45543/Polystichum_sorus_L.jpg?revision=1&size=bestfit&width=1047&height=523)
![A cross section through a sorus that has a false indusium](https://bio.libretexts.org/@api/deki/files/45544/Dicksonia_sorus_L.jpg?revision=1&size=bestfit&width=891&height=657)
Full Life Cycle Diagram
![fern life cycle diagram with important parts labeled](https://bio.libretexts.org/@api/deki/files/27324/Fern_Life_Cycle.png?revision=1)
Note: Images by Jon Houseman are licensed in Wikimedia as CC BY-SA. In an email with Maria Morrow, he agreed that we could use the CC BY-NC license for these images.