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Ferns are vascular plants which do not produce seeds or flowers but propogate by dispersing microscopic spores released from their sporangia. With about 12,000 species world wide they are probably slightly less numerous than the mosses and the third-largest vascular plant group. Most of our native ferns have have divided or compound leaves (fronds) that grow from rhizomes (underground stems). Stem vascular bundles are arranged in a Siphonostele. Developing leaves are coiled like the scroll of a violin and are called 'fiddleheads'. Sporangia are borne in aggregations (sori) on the leaf undersurface or in some species on specialized fertile fronds that are diferent in appearence from the vegetative leaves. Horsetails (Equisetaceae), have unbranched or branched green, jointed aerial stems with small scale-like leaves and bear their sporangia on cone-like stobili. Despite their different appearence, horsetails are part of the fern evolutionary lineage. Ferns and horestails are more closely related to seed plants than to Lycophytes despite their sharing ancestral life-cycle features with Lycophytes.
