Equisetum
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Authority
Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.
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Family
Equisetaceae
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Scientific Name
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Description
Genus Description - Terrestrial; rhizomes 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 (internal to the stem grooves) and carinal (internal to the stem ridges) canals; leaves small, white to black, whorled, fused to form a sheath at the nodes; aerial axes perennial or annual, stems monomorphic (in ours) or dimorphic; stem ridges with silica tubercles, grooves with narrow or broad bands of stomata; sporangia borne abaxially on tightly packed peltate sporophylls, those forming the terminal strobili on the main stems and branches; spores homosporous, green, each with four elaters; x=108.
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Discussion
Lectotype (chosen by Farwell, Mem. New York Bot. Gard. 6: 464. 1916): Equisetum arvense L.; E. fluviatile L. is sometimes regarded as lectotype; see discussion and additional synonymy by Pichi Sermolli, Webbia 26: 179, 1971
Equisetum is terrestrial or of moist to swampy 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 and north-temperate regions. Twelve species occur in North America, three in Mexico. Hybridization is common in the genus, some hybrids being as common as one or more of the parents. Recent molecular evidence suggests that Equisetum is most closely related to basal ferns (Pryer et al., 2001). We are grateful to R. L. Hauke for identification of Mexican specimens of Equisetum and for valuable discussions regarding their interpretation.