Equisetales

The Equisetales are an order of living and extinct spore-bearing plants that exhibit whorled growth in branching and leaf insertion. The modern forms, Equisetum spp., known as the horsetails or scouring rushes are herbaceous plants with whorled photosynthetic branches, and highly-reduced whorled leaves. Ancient members of this group, such as Calamites, grew to heights over 30 meters. They produced wood to reach these heights and displayed laminate photosynthetic leaves for photosynthesis (Annularia)

Ecology & Form

  • One living genus (Equisetum); ~60 fossil genera including Calamites

  • Almost all members, living or extinct, inhabit wetland environments

  • Modern forms are known to absorb macromolecules from soil

Stems

  • Whorled branches in the "horsetails"; the "scouring rushes" usually lack branches or have smaller side branches

  • Distinct nodes and internodes (bamboo-like appearance)

    • Internodes are hollow; nodes are solid

    • Living forms are herbaceous; extinct forms exhibited a vascular cambium with wood production

    • Periderm has been observed in the fossil Arthropitys (Cichan and Taylor 1983)

  • Pseudomonopodial growth

    • Upright stem and side branches formed from unequal division of an apical cell


Leaves

  • Whorled leaves at nodes

  • Highly reduced in living forms (e.g. Equisetum)

  • Laminate and photosynthetic in extinct forms


Roots

  • True roots are present


Reproduction

  • Sporangia aggregated into a cone (=strobilus)

  • Sporangia are on recurved stalks, called sporangiophores, and inserted in a whorled fashion

  • Eusporangiate: Sporangia are larger with many spores

  • Spores exhibit arm-like elaters, which aid in wind dispersal

    • Elaters react to humidity; opening in dry air and wrapping around spore in humid air

Geologic Range

Above: close-up of E. fluviatile cone. Below the cone the reduced leaves are visible

Below: cross-section of Equisetum cone showing recurved sporangia

Diversity

The Equisetales has several families, including:

Archaeocalamitaceae †

Protocalamostachys

    • Bateman 1991

    • Early Mississippian of the UK

    • P. arranensis †

    • P. farringtonii †

Peltotheca furcata †

Calamitaceae †

Calamocarpon insignia †

Calamostachys †

Cruciaetheca †

    • Cúneo and Escapa 2006

    • Early Permian of Argentina

    • Cr. patagonica

    • Cr. feruglioi

Mazostachys pendulata †

Paracalamitina striata †

Palaeostachya †

Pendulostachys cingulariformis †

Weissistachys kentuckiensis †

Above: Reconstruction of Calamites from the Carboniferous

Above: Cast fossil of Calamites

Tchernovianceae †

Gondwanostachyaceae †

Equisetaceae

Equisetum

  • E. arvense

  • E. bogotense

  • E. clarnoi †

  • E. dimorphum †

  • E. diffusum

  • E. fluviatile

  • E. fluviatoides †

  • E. giganteum

  • E. haukeanum †

  • E. hyemale

  • E. laevigatum

  • E. laterale †

  • E. myriochaetum

  • E. palustre

  • E. pratense

  • E. ramosissimum

  • E. scirpoides

  • E. similkamense †

  • E. sylvaticum

  • E. telmateia

  • E. thermale †

  • E. vancouverense †

  • E. variegatum

Equisetites †

  • E. arenaceus †

  • E. lyellii †

  • E. bogotense †

Neocalamites †

Neocalamostachys arrondoi †

Schizoneura †

Spaciinodum collinsonii †

Above: E. arvense in a woodland leaf litter

Above: Large stems of E. myriochaetum

Incertae sedis

  • Phyllotheca †

Above: Phyllotheca