ORDER PSILOTALES
Raven 7th p. 398-399; 8th, p. 415-417
The Psilotaceae is made up of two extant genera, Psilotum and Tmesipteris. This group is characterized by a dichotomously branched conspicuous sporophyte and an inconspicuous subterranean gametophyte. We will be examining Psilotum which is native to both tropical and subtropical locations. The sporophyte has a rhizome but not true roots, and simple stem with a very simple vascular system. (Review the various stele types, link at bottomof the page). Sporangia produce only one type of spore i.e. they are homosporous. Because of their simple anatomy it was believed until recently that the Psilophytes represented an ancient lineage. Molecular evidence indicates that they are actually within the monilophyte clade.
First observe the branching pattern of the entire plant. Psilotum is a good, uncomplicated example of a dichotomous branching pattern. Note the sporangia borne at intervals on the stems.
