Equisetum hyemale var. affine (Engelm.) A.A.Eaton

Authority

Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.

Family

Equisetaceae

Scientific Name

Equisetum hyemale var. affine (Engelm.) A.A.Eaton

Description

Species Description - Stems erect, unbranched, bluish green, to 2.2 m tall, 5–10 mm diam., unbranched except on damaged plants; sheaths with length to width ratio of ca. 1:1 with two dark girdles, one at distal edge, the other at middle of sheath, ash gray between; stomata in single lines, one line on each side of a groove; ridges 14–50, with tubercles; stem cross sections with carinal collenchyma extending to the vascular bundles, vallecular collenchyma absent to small; endodermis of double common type; strobili terminal on stems, ca.15 mm long, each with a black apiculum; 2nx216 (Canada, USA).

Discussion

Equisetum robustum A. Braun ex Engelm. ? affine Engelm., Amer. J. Sci. Arts 46: 88. 1844. Equisetum hyemale L. subsp. affine (Engelm.) Calder & Roy Taylor, Canad. J. Bot. 43: 1387. 1965. Type. U.S.A. Grassy clayey banks of Mississippi River below Jefferson Barracks, Aug 1843, Engelmann s.n. (MO; isotype US!). For full synonymy, see Hauke (1963).

Unverified, Doubtful, or Mistaken Reports. Ags (Garci´a 2388, HUAA, and three other collections, cited by Siqueiros-Delgado & Gonza´lez-Adame, 2004, but not verified).

Equisetum hyemale var. hyemale occurs in Eurasia and has stem ridges always bituberculate and teeth soon falling (vs. convex to bituberculate and teeth persistent to falling in var. affine). The dark banding of the sheaths is distinctive of E. hyemale, but often the banding is irregular or even absent. This character is quite variable in Mexico and has led some to believe Equisetum laevigatum to be more widespread than it actually is. Young E. hyemale has longer than usual sheaths that often lack the lower dark bands, resembling those of E. laevigatum. Malformed, non-green spores, evidenced by whitish powdery material in the sporangia and unopened strobili, are evidence of hybrids. Hybrids and juvenile specimens are often difficult to identify with confidence. Equisetum hyemale hybridizes with E. laevigatum (= E. xferrissii Clute) in northwestern Mexico (BCN, Chih, Dgo) in areas of overlap. Stem cross sections show vallecular collenchyma prominent (as in E. laevigatum), often extending to the vallecular canal (as in E. laevigatum), and the carinal collenchyma usually extending nearly to the vascular bundles (as in E. hyemale) (Fig. 144F). Equisetum hyemale x myriochaetum (E. xhaukeanum Mickel) is widespread (Sin, Jal, Mich, Gro, Qro, Mor, Me´x, NL, SLP, Hgo, Ver, Pue, Oax, Chis, Guat) and nearly as common as its parents, both of which have broad distribution. Stems are tall, unbranched to irregularly and sparsely branched or much branched, to 2.5 m tall, 3.5–8.5 mm diam., with 14–36 ridges; stem sheaths with length to width ratio of 1:1.7; proximal sheaths with two dark bands and ash-gray between; distal sheaths each with single marginal band and same color as stem; teeth mostly deciduous; branch ridges with irregular to saw-toothed tubercles; strobili strongly apiculate, with malformed spores. This hybrid is extremely variable, sometimes closely resembling one or the other parent. The irregular and mixed tubercles/saw teeth can be used to determine E. x haukeanum. The nodal sheaths resemble those of E. hyemale near the base and those of E. myriochaetum distally and distinguish both branched and unbranched stems. Generally, the irregular branching of E. xhaukeanum is not found in E. myriochaetum. Stem cross sections (Fig. 144e) show carinal collenchyma touching the vascular bundles, the vallecular collenchyma varying from obsolete to touching the vallecular canal, and endodermis of the double common type.

Distribution

Usually in moist areas by streams or seeps, oak forests, pine-oak forests; 1600–3000 m. Widespread in Canada, USA; Mexico; Guat; northeasternmost Asia.

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