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
Classification
└Equisetales
Geologic Range
Mississippian - present
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 †
Escapa and Cúneo, 2005
Early Permian of Argentina
Calamocarpon insignia †
Baxter 1963, 1964; Good 1975
Pennsylvanian of the USA
Calamostachys †
- Ca. americana
Pennsylvanian of USA
- Ca. binneyana
Pennsylvanian of UK and USA
- Ca. casheana
Williamson and Scott 1894; Lacey 1941
Pennsylvanian of USA
- Ca. inversibractis
Pennsylvanian of USA
Cruciaetheca †
Cúneo and Escapa 2006
Early Permian of Argentina
Cr. patagonica
Cr. feruglioi
Mazostachys pendulata †
Kosanke 1955; Good 1975
Pennsylvanian of USA
Paracalamitina striata †
Palaeostachya †
Pennsylvanian of USA
P. andrewsii
P. decacnema
Pendulostachys cingulariformis †
Pennsylvanian of USA
Weissistachys kentuckiensis †
Rothwell and Taylor 1971a, 1971b
Pennsylvanian of USA
Above: Reconstruction of Calamites from the Carboniferous
Above: Cast fossil of Calamites
Tchernovianceae †
Gondwanostachyaceae †
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