Flora of the Canadian Arctic Archipelago
English: Horsetails, scouring rushes.
Equisetaceae, Horsetail or Scouring rush family.
Vegetative morphology. Plants 2–30(–100) cm high (on continental North America); perennial herbs; not caespitose; jointed fertile stems without pigmentation, or with pigmentation. Only fibrous roots present. Roots pallid-brown, or red-brown, or black. Ground level or underground stems horizontal, or vertical; rhizomatous, or stoloniferous; elongate, or compact; 0.4–1(–2) mm wide. Ground level or underground stems scales present (reduced leaves); 3–4, or 5–12; dull brown, or shiny black, or dull black; glabrous. Aerial stems developed; erect, or prostrate; conspicuously jointed with nodes covered by whorls of tiny leaf teeth fused for part of their length into sheaths that are tipped with teeth; filiform, or not filiform. Aerial stem ridges 3–8(–12); the same number as that of the leaf teeth at each node. Leaves absent or leaf teeth; leaf teeth (in whorls distributed along the stem). Leaf teeth persistence persistent, or annual, dying at the end of the first season. Leaf teeth 0.5–3 mm. Leaf teeth 0.05–3 mm. Leaf teeth dull with pale centres and dark brown margins or dull and black or shiny black or brown.
Reproductive morphology. Plants with sporangia, or vegetative leaves without obvious spore-bearing organs (sometimes appearing so, because cones mature late winter and are often not present during the summer). Sporangia in terminal cone-like structures. Aerial stems circular or oval in cross-section, or squarish in cross-section.
General notes. Named from the Latin equus, horse, and seta, bristle, referring to the coarse black roots of E. fluviatile L. Two of the three species found in the Canadian Arctic Archipelago belong to subg. Hippochaete (J. Milde) Baker (E. scirpoides, E. variegatum), the third to subg. Equisetum (E. arvense).
Stems (and branches, if any) jointed, fluted, hollow, often rough from silica deposited in cells; leaves borne in whorls at each node, fused at the base to form a sheath, but with free tips. Sporangia are grouped in terminal strobili (cones) having polygonal segments.
Illustrations. • Horsetails. Family and genus characterised by the presence of fertile cones bearing sporangia on the underside of the sporophylls. Note two small flies searching for spores. Aiken 99–025. CAN.
This publication is available on the internet (posted May 2011) and on CD-ROM (published in 2007). These versions are identical in content, except that the errata page for CD-ROM is accessible on the main index page of the web version.
Recommended citation for the web-based version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. NRC Research Press, National Research Council of Canada, Ottawa. http://nature.ca/aaflora/data, accessed on DATE.
Recommended citation for the CD-ROM version of this publication: Aiken, S.G., Dallwitz, M.J., Consaul, L.L., McJannet, C.L., Boles, R.L., Argus, G.W., Gillett, J.M., Scott, P.J., Elven, R., LeBlanc, M.C., Gillespie, L.J., Brysting, A.K., Solstad, H., and Harris, J.G. 2007. Flora of the Canadian Arctic Archipelago: Descriptions, Illustrations, Identification, and Information Retrieval. [CD-ROM] NRC Research Press, National Research Council of Canada, Ottawa..