Eusporangiate fern

Eusporangiate ferns are vascular spore plants, whose sporangia arise from several epidermal cells and not from a single cell as in leptosporangiate ferns. Typically these ferns have reduced root systems and sporangia that produce large amounts of spores (up to 7000 spores per sporangium in Christensenia).

There are four extant eusporangiate fern families, distributed among three classes. Each family is assigned to its own order.

• Class Psilotopsida
  • Order Psilotales, family Psilotaceae – Whisk ferns (2 genera, about 17 species)
  • Order Ophioglossales, family Ophioglossaceae – Adder's-tongues (5 genera, about 80 species)
• Class Equisetopsida
  • Order Equisetales, family Equisetaceae – Horsetails (1 genus, about 15 species)
• Class Marattiopsida
  • Order Marattiales, family Marattiaceae – Marattoid ferns (6 genera, about 500 species)

The following diagram shows a likely phylogenic placement of eusporangiate fern classes within the vascular plants.

Cladistics

While it is generally accepted that the leptosporangiate ferns are monophyletic, it is considered to be likely that the eusporangiate ferns, as a group, are paraphyletic. In each of the three examples from recently published studies, shown in the following table, it can be seen that, together, the four eusporangiate fern families do not form a single clade.

Pryer & Schuettpelz, 2009

Rai & Graham, 2010

Lehtonen, 2011

References

• Hogan, C.Michael. 2010. Fern. Encyclopedia of Earth, National Council for Science and the Environment. topic ed. Saikat Basu
• Sporne, K. R. 1962. The morphology of pteridophytes, the structure of ferns and allied plants. pp. 127–135. Hutchison & Co. London.