Psilotum nudum

When I first learned about this plant, it was growing as a weed in the greenhouse at Ohio University —its presence was tolerated primarily because we used it regularly in the undergraduate Plant Morphology, Systematics, and Paleobotany courses. Now, I live in Florida and it grows along the route where I walk my dog every morning.

Psilotum growing wild

Psilotum growing wild

This plant is facinating becasue it looks rather similar to some of the fossils of the earliest land plants; somewhat like what we think the ancestor of all living ferns and seed plants was like. The green axes branch dichotomously and in three dimentions, bearing lateral organs that look like tiny leaves sometimes called “prophylls.” Studies indicate that these organs they probably are reduced leaves in <i>Psilotum</i>, but they lack vascular tissue and are similar to the enations that ornimented the leafless sporophytes of many early land plants.

P1070921

Psilotum with yellow synangia

P1070918

branching Psilotum with prophylls

Shoot tip

Shoot tip

One recent Saturday I decided to harvest a bit of this plant and make some simple sections by hand. The images below are stained with safranin or methylene blue to show the different cell types. The images in this little tour may be used for teaching purposes, just send me an email of leave a comment to let me know!

MethyleneStele2

<i>P. nudum</i> stele, stained with Methylene Blue

SafraninStele

<i>P. nudum</i> stele, stained with safranin

Here is a close up of the outer part of the stele. The thick-walled, dark red cells are the water-conducting xylem cells

SafraninStele2scale

Close up of stele, stained with Safranin

and this is a cross-section of the stele in the rhizome

rhizomeMethylene

Cross section of the rhizome, stained with Methylene blue. Note the casparian strip in yellow. The scale should read 120, not 128um. I’ll fix that soon.

Here is a low-mag shot of the rhizome, with a new branch pointed downward

psilotum2x4x_54

Cross-section of the rhizome with a branch

And anther close up

Tracheids

Close up of the branch in the image above. This shows the xylem cells in the middle of the banch. They are obvious because of the characteristic helical thickenings.

and lastly

Synangia2

small white spores in the sporangia (three sporangia fuzed into a synangium)

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