Monographs Details: Equisetum
Authority: Mickel, John T. & Beitel, Joseph M. 1988. Pteridophyte Flora of Oaxaca, Mexico. Mem. New York Bot. Gard. 46: 1-580.
Description:Genus Description - Terrestrial; rhizome subterranean, perennial, long-creeping, branched; aerial stems erect, hollow, grooved, jointed, simple or with whorled branches, generally with a large central canal and smaller vallecular and carinal canals; leaves small, white to black, whorled, fused to form a sheath at the nodes; aerial axes perennial or annual, stems monomorphic or dimorphic (monomorphic in ours); stem ridges with silica tubercles, grooves with narrow or broad bands of stomata; sporangia borne on underside of closely fitted peltate sporophylls that form the terminal strobili on main stem and branches; spores homosporous, green, with four elaters; gametophytes green.
Discussion:Lectotype (chosen by Farwell, Mem. New York Bot. Gard. 6: 464. 1916): Equisetum arvense Linnaeus; E. fluviatile is sometimes regarded as lectotype; see discussion by Pichi Sermolli (Webbia 26: 179. 1971).
For additional synonymy, see Pichi Sermolli (Webbia 26: 179. 1971).
Equisetum is terrestrial on wet lands, forming small to extensive stands through the wide-creeping, much-branched rhizomes. The genus is widespread, but with only 15 species, mostly of boreal temperate regions. Twelve species occur in North America, one in southern Asia, and three in Latin America. Four taxa occur in Oaxaca: one northern species, one tropical species, one hybrid between the former two species, and one widespread hybrid between two giant tropical species with one parent not known from Oaxaca. All four are of subg. Hippochaete.
There are two distinct subgenera: Equisetum often dimorphic, much-branched, with stomata level with stem surface; Hippochaete less branched, never dimorphic, stomata sunken below the stem surface.
Reference: Hauke, R. L. 1963. A taxonomic monograph of the genus Equisetum subgenus Hippochaete. Beih. Nova Hedwigia 8: 1-123.