Primitive fern allies, such as psilotum and equisetum, are ancient plants.
For information about giant equisetum, please visit Dr. Chad Husby's site, http://www.fiu.edu/~chusb001/giant_equisetum.html.
I hope to some of these plants occasionally, starting in spring of 2010.
There are two species of psilotum, and a hybrid between the two.
Psilotum do not have true roots. Above ground stems are green, and below ground they are translucent, or brown, and may be covered with small hairs.
Psilotum complanatum is rare in cultivation, and difficult to grow. It has flattened stems. Nice photos of this species may be viewed at the flickr page of Dr. Chad Husby, http://www.flickr.com/photos/calamites/4955495315/. Chad took the photo below.
Psilotum nudum is nearly cosmopolitan, growing in tropical and warm-temperate areas worldwide. In the U.S. it is native to the southeast, from Florida to the Carolinas, along the coastal plain.
This species may be terrestrial or epiphytic. In South Florida, it is a common weed in nursery plants.
The plant below volunteered in the Florida International University greenhouse. It was shared by Dr. Chad Husby, now with the Montgomery Botanical Garden.
Probably Psilotum nudum, this form stays small. The specimen below is in a 4" pot.
The photos below are P. x Intermedium, which is a cross of P. nudum x P. complanatum. This hybrid generally looks like P. nudum, but the stems are often flat, rather than triangular.