7.3: Gnetophytes
- Page ID
- 35345
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Gnetophytes represent an anatomically and genetically difficult group to classify. They have several traits in common with angiosperms, such as vessel elements in the xylem, double fertilization, and a covering over their seeds. Even their leaves are angiosperm-like, with netted venation. However, these traits are convergently evolved, meaning that angiosperms and gnetophytes each evolved these traits separately. Genetically, recent studies have placed the gnetophytes as a sister group to the Pinaceae (pine family) within the conifers. This would mean that pines, firs, and spruces are more closely related to strange gnetophytes like Ephedra than they are to other conifers like redwoods, cedars, and Pacific yew. However, the true nature of this evolutionary relationship remains murky and contentious.
Characteristics of Gnetophytes
- Angiosperm-like features: vessel elements, double fertilization, fruit-like ovule coverings
- Dioecious. Female plants have covered ovules, while male plants have pollen cones.
- Leaves xerophytic with opposite arrangement
- Primarily insect pollinated; brightly colored seeds are dispersed by birds
Notable Gnetophytes
Welwitschia mirabilis
This strange plant grows in the desert of Namibia. It has two large leaves that grow from a basal meristem.
![A plant with two large leaves growing opposite of each other seemingly directly from the ground.](https://bio.libretexts.org/@api/deki/files/45567/1.jpg?revision=1&size=bestfit&width=775&height=472)
![A much larger Welwitschia plant, the leaves are piling on top of themselves and there appear to be more than two, as the leaves have split many times](https://bio.libretexts.org/@api/deki/files/45568/2.jpg?revision=1&size=bestfit&width=641&height=480)
![A large cluster of megastrobili. They are composed of tightly overlapping megasporophylls and are slightly swollen in the center.](https://bio.libretexts.org/@api/deki/files/45569/3.jpg?revision=1&size=bestfit&width=711&height=472)
![A close view of a single megastrobilus. The megasporophylls are relatively large and overlap in a scale-like fashion](https://bio.libretexts.org/@api/deki/files/45570/4.jpg?revision=1&size=bestfit&width=676&height=507)
![Many smaller, salmon-colored, pointier microstrobili in the center of a Welwitschia plant](https://bio.libretexts.org/@api/deki/files/45571/5.jpg?revision=1&size=bestfit&width=705&height=470)
![Thin, dry microstrobili with many small microphylls](https://bio.libretexts.org/@api/deki/files/45572/6.jpg?revision=1&size=bestfit&width=643&height=430)
Ephedra spp.
![A thin stem with two tiny, scale-like leaves emerging from either side of a node](https://bio.libretexts.org/@api/deki/files/45573/7.jpg?revision=1&size=bestfit&width=677&height=380)
![Thin green stems end in swollen red structures that appear to be separated into a few different segments](https://bio.libretexts.org/@api/deki/files/45574/8.jpg?revision=1&size=bestfit&width=716&height=402)
![Two small cone-like strobili with structures emerging that look like anthers (small, yellow, and branching)](https://bio.libretexts.org/@api/deki/files/45575/9.jpg?revision=1&size=bestfit&width=766&height=430)