Osmundales

Order Osmundales

Members of the Osmundaceae are found in tropical and temperate regions. This group includes the popular cinnamon fern, Osmundastrum cinnamomaea, and royal fern, Osmunda spectabilis. Economic importance includes these cultivated ornamentals, as well as other (e.g., Todea barbara) and local uses for fiber and food. Osmunda regalis is used in brewing a Celtic ale. This order is considered to be most ancestral of the true (leptosporangiate) ferns

Sporophyte (spore-bearing phase)

Vegetative features

Stem, anatomy

  • Anatomy is complex with an ectophloic siphonostele (phloem on the outside of discrete xylem ring) often conduplicate or twice conduplicate in cross-section

Stem, morphology

  • The stems are erect (some taxa being arborescent “tree ferns”)

Leaves

  • The leaves are 1-2-pinnate or pinnatifid, stipulate, with stipules at the base of petioles,

  • Dimorphic fronds with either fertile and sterile leaves or with fertile and sterile leaf segments

  • Sori and indusia are absent, the sporangia occurring on the abaxial surface of leaves or leaf segments

Roots

  • Adventituous roots

Reproductive features

  • Sporangia tend to be born on fertile fronds with non-laminar pinnules, except Todea and Leptopteris

  • Sporangia are large with 128 to 512 spores; dehiscence by an apical slit

    • The annulus is lateral

    • The spores are green, subglobose, and trilete

Above: Ferns in the Osmundales. A, B. Leptopteris superba, with 2-3-pinnatifid leaves. C. Osmundastrum cinnamomaea, cinnamon fern. D. Claytosmunda claytoniana, interrupted fern. E. Todea barbara, with bipinnately compound leaves. (Images taken by Lawrence Jensen)

Gametophyte (gamete-bearing phase)

  • Gametophytes, which are green, photosynthetic, and surficial

  • They are large and heart-shaped

Classification

└Tracheophytes

└Euphyllophytes

└Ferns (Polypodiopsida)

└Polypodiidae

└Osmundales

Diversity

  • 1 extant family (Osmundaceae); 4-6 extant genera; 18–25 known species

    • Claytosmunda

    • Leptopteris

    • Osmunda

    • Osmundastrum

    • Plenasium

    • Todea

  • 1 extinct family (Guaireaceae) known from the Permian

Geologic Range

  • Several extinct taxa ranging back to the Late Paleozoic

    • Thamnopteris †

    • Chasmatopteris †

    • Osmundacaulis †

    • Palaeosmunda †

    • Millerocaulis †

    • Aurealcaulis †

    • Todites †

    • Anomopteris †

    • Osmundacidites †

    • Osmundites †

    • Osmundopsis †

    • Zhongmingella †