Equisetum laevigatum

Equisetum laevigatum A.Braun
(Latin: laevigatus, smooth, slippery, polished)

Local names: smooth horsetail, smooth scouring-rush, Braun’s scouring-rush, Kansas horsetail, Kansas scouring-rush, summer scouring-rush, cola decaballo, cañuela

Aerial stems usually annual, monomorphic, unbranched (unless damaged or abnormal), 20–150 cm tall, typically 3–5(–7) mm in diam, (the plants tending to be less robust than those of E. hyemale), with 10–32 ridges, the stem surface ± smooth, usually bright green to yellowish green at maturity; leaf sheaths longer than wide (length/width ratio ca. 2:1), usually green except for thin dark band where teeth are attached, the teeth promptly shed (note: the basal few nodes often with sheaths having a basal dark girdle, thus ± resembling those of E. hyemale); leaves 10–32 per node (number evident as teeth of sheaths); cones ellipsoid, 1–2 cm long, 7–10 mm in diam., the apex usually rounded or with a very small apiculum; 2n = 216 (Hauke 1993). Widely scattered in TX, mainly in the w ¾ of the state (e.g., Hemphill Co., C. Rowell 4043, Mason Co., S.E. Wolf 5167; Potter Co., G. Nesom & O’Kennon LAMR326, all BRIT) (solid dots on the county distribution map represent specimens identified by J. Peck and G. Diggs, while open circles are herbarium and literature records identified by other authorities—see discussion under E. hyemale); s Canada and through much of U.S. except ne and se; also n Mexico. Sporulating May–Jul. [E. funstonii A.A. Eaton, E. kansanum J.F. Schaffn., E. laevigatum subsp. funstonii (A.A. Eaton) Hartman] Hauke (1993) noted that, “Schaffner named this species Equisetum kansanum because he applied the name E. laevigatum to what we now know is the hybrid E. ×ferrissii.” This species, E. hyemale, and the hybrid E. ×ferrissii are often very difficult to distinguish and appear to intergrade when only young, anomalous, or incomplete material is available (see discussions under E. hyemale and the hybrid, E. ×ferrissii). Smooth horsetail is sometimes sold in nurseries for use in water gardens; in these settings it can be quite aggressive. Poisonous (Burlage 1968; Burrows & Tyrl 2001).

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