5.1: Hornworts
- Page ID
- 35329
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Hornworts, Phylum Anthocerotophyta
![A hornwort showing both sporophyte and gametophyte generations](https://bio.libretexts.org/@api/deki/files/26847/Hornwort.jpg?revision=1&size=bestfit&width=719&height=391)
![Diagram of a hornwort life cycle](https://bio.libretexts.org/@api/deki/files/45309/1920px-Hornwort_life_cycle.svg.png?revision=1&size=bestfit&width=743&height=828)
Gametophyte Morphology
Hornwort gametophytes are exclusively thalloid, often with compartments of mutualistic cyanobacteria from the genus Nostoc. Cells within the gametophyte are monoplastidic, containing one large chloroplast in each cell. On the exterior of the thallus, simple pores allow for gas exchange (no guard cells, meaning pores are permanently open).
![A piece of a thallus viewed under a microscope. The cells of the thallus each have a single, large plastid.](https://bio.libretexts.org/@api/deki/files/45310/1.jpg?revision=1&size=bestfit&height=635)
![Close up of monoplastidic cells, each with one large plastid](https://bio.libretexts.org/@api/deki/files/30585/3582216778_dc710ed305_c.jpg?revision=1&size=bestfit&width=585&height=377)
Sporophyte Morphology
Hornwort sporophytes are comprised of a linear sporangium that lacks a seta. It grows from a basal meristem, meaning the cells at the apex are the oldest. When you see the sporangia mature, this becomes more obvious, as the tip dries out first and dehisces (splits apart) to release the spores. Unlike the gametophyte, the sporophyte possesses true stomata for gas exchange.
![A cross section through a hornwort sporangium.](https://bio.libretexts.org/@api/deki/files/30586/Inked4027210418_d6992c492b_w_LI.jpg?revision=1)
![clusters of ornamented spores inside a hornwort sporangium](https://bio.libretexts.org/@api/deki/files/30587/4026457635_893e27563c_w.jpg?revision=1)
![A view through a microscope of the tip of a sporophyte, many dark globose structures (spores) are visible.](https://bio.libretexts.org/@api/deki/files/45311/2.jpg?revision=1&size=bestfit&width=595&height=521)
![six large, brown, globose structures covered in a network of small spines.](https://bio.libretexts.org/@api/deki/files/45312/1920px-Anthoceros_agrestis_(a%252C_150910-484827)_6320.jpg?revision=1&size=bestfit&width=536&height=402)