Type. Mexico. Veracruz: Misantla, “in sylvis humidis,”
Schiede & Deppe 833 (B!).
Equisetum myriochaetum has flattened sheath segments (also
found in E. xhaukeanum) and often has poor tubercle development.
Generally, large Mexican horsetails with regular whorls
of branches belong to E. myriochaetum. Equisetum myriochaetum
crosses with E. giganteum to form E. xschaffneri: Equisetum
xschaffneri Milde, Verh. Zool.-Bot. Ges.Wien 11: 345. 1861 (Fig.
144d). Type. Mexico. Veracruz: Orizaba, Schaffner 315 (B?). For
synonyms, see Hauke (1963). Its stems have regular whorls of
branches and are 2–4 m tall (to 7 m tall in Costa Rica), 3–22
mm diam., with 12–48 ridges; vascular bundles each with its own
endodermis; carinal collenchyma extending to vascular bundles;
vallecular collenchyma extending to the vallecular canal or nearly
so; sheaths green to brown at bases; stomata in bands of 1–2(–3)
in each groove; branches with 6–8 ridges with saw teeth or irregular
tubercles; strobili terminal on branches and main stems,
acute or each with a slight apiculum; spores malformed.
Equisetum x schaffneri rarely occurs from Mexico to Peru, in
Mexico at 500–950 m elevation (Tam, Ver, Pue, Oax, Chis).
Equisetum giganteum is not known to occur in Mexico, and
Hauke (1963) suggested that E. x schaffneri is dispersed by an
occasional good spore. Equisetum x schaffneri can be distinguished
by its malformed, non-greens spores, intermediacy in
number of rows of stomata (1–2 rows on each side of grooves);
E. giganteum with broad stomatal band, 3–4 rows (vs. E. myriochaetum in one row on sides of each groove), branch ridges
with flattened tubercles (vs. stomata in single lines and branch
ridges with curved saw teeth in E. myriochaetum), and endodermis
around individual bundles, as in E. giganteum (vs. continuous
in E. myriochaetum).
Terrestrial in swampy or marshy places, usually seepage areas, usually more or less exposed, in pine-oak forests, grassy flats, lower montane rain forests; (350–)700–2420 m. Mexico; Guat, Hond, Nic, CR, Pan; Col, Ven, Ec, Peru. Selected Specimens Examined. Chis (Breedlove 21386, NY). Col (González s.n., 25 May 1977, IBUG). Gro (Lorea 1138, FCME). Gto (Pérez Calix & Carranza 2898, IEB). Hgo (Gimate 842, NY). Jal (Cochrane et al. 5186, IBUG, UC, WIS). Méx (Hinton 2402, NY, US). Mich (Moore et al. 5739, UC). Nay (McVaugh & Koelz 762, NY). NL (Sánchez et al. 438, MEXU). Oax (Hallberg 1020, ENCB, MICH, US). Pue (Kelly 567, US). Qro (Servi´n 1375, IEB). Sin (Vega A. 863, IEB). SLP (Pringle 3294, BR, NY, UC, US). Tam (González Medrano 16961, MEXU). Ver
(Copeland herb. 164, GH, MICH, UC, US).