Lycopodiophyta

The Division Lycopodiophyta (sometimes called Lycophyta or Lycopods) is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant (living) vascular plant division at around 410 million years old. These species reproduce by shedding spores and have macroscopic alternation of generations, although some are homosporous while others are heterosporous. Members of Lycopodiophyta bear a protostele, and the sporophyte generation is dominant. They differ from all other vascular plants in having microphylls, leaves that have only a single vascular trace (vein) rather than the much more complex megaphylls found in ferns and seed plants.

Classification

There are around 1,200 living (extant) species of Lycopodiophyta which are generally divided into three orders (Lycopodiales, Isoetales, and Selaginellales); in addition there are extinct groups. There is some variation in how the extant orders are grouped into classes: they may be put into a single class; they may be put into two classes, with the Isoetales and Selaginellales combined into one class; or they may be put into three classes, one order in each. The system which uses two classes for extant species is: