Explanation

The lycophytes separated from the rest of the early land plants, evolved adequate reproductive, supportive, and transport systems. Three groups of extinct vascular plants were prevalent in Devonian times; the rhyniophytes, zosterophylls, and trimerophytes. The oldest known vascular plant is Cooksonia, a 6.5 centimeter- tall plant with dichotomously branched (forking into two) leafless stems with sporangia at their tips. Only bits and pieces have so far been recovered and no rhizomes or below ground parts have been found. It is a rhyniophyte and its relatives were extinct by mid-Devonian time