维管束无核植物

There are three major groupings covering the plant life on Earth—nonvascular plants, seedless vascular plants, and seed plants.

The seedless vascular plants were the first to evolve specialized vascular systems—an adaptation that helped them become the first tall plants on Earth. Today, seedless vascular plants are represented by lycophytes and monilophytes. 

Lycophytes include clubmosses, spikemosses, and quillworts. Notably, none of the lycophytes are true mosses, which are nonvascular plants. Monilophytes include ferns, horsetails, and whisk ferns and their relatives.

Like all plants, seedless vascular plants display an alternation of generations in their life cycle, as shown here using a fern plant as an example. 

This means that they spend part of their life cycle as a haploid gametophyte, and the other part as a diploid sporophyte. 

Like nonvascular plants, seedless vascular plants reproduce using spores, rather than seeds. The spores are haploid, and are dispersed by structures called sori, clustered on the underside of the leaves. 

The sori themselves contain many sporangia. Upon reaching maturity, these sporangia open, dispersing the haploid spores. The spores then grow vi