Flora of North America species comparison

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Equisetum fluviatile

Equisetum ×ferrissii

pipes, prêle fluviatile, river horsetail, swamp horsetail, water horsetail

Ferris' horsetail, Ferriss' horsetail, Ferriss' scouring-rush
Sheaths

squarish in face view, ca. 4–10 × 4–10 mm;

teeth black, occasionally with narrow white border, 12–24, narrow, 2–3 mm.

elongate, 7–17 × 3–12 mm, becoming dark-girdled with age;

teeth 14–32, articulate and promptly shed or persistent.
Aerial stems

monomorphic, green, unbranched or branched, 35–115 cm;

hollow center large, to 9/10 stem diam.;

vallecular canals absent.

having basal part persisting over winter, unbranched, 20–180 cm;

lines of stomates single;

ridges 14–32.
Branches

when present only from midstem nodes, spreading, hollow, ridges 4–6, valleys rounded; 1st internode of each branch shorter than subtending stem sheath;

sheath teeth narrow.

Cone

apex pointed;

spores white, misshapen.
2n

=216.

Equisetum fluviatile

Equisetum ×ferrissii
Phenology Cones maturing in summer. Cones maturing in late spring–early summer but spores not shed.
Habitat Standing in water, in ponds, ditches, marshes, swales Moist lakeshores, riverbanks, roadsides, prairies
Elevation 0–1500 m (0–4900 ft) 0–2500 m (0–8200 ft)
Distribution
from FNA
CT; DC; DE; IA; ID; IL; IN; MA; MD; ME; MI; MN; MT; ND; NE; NH; NJ; NY; OH; OR; PA; RI; SD; VA; VT; WA; WI; WV; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; SPM; Alaska including the Aleutian Islands; Eurasia s to n Italy; China; Korea; Japan
[WildflowerSearch map]
[BONAP county map]
from FNA
AR; AZ; CA; CO; CT; DC; DE; IA; ID; IL; IN; KS; MA; MD; ME; MI; MN; MO; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SD; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; ON; QC; SK; n Mexico including Baja California
[WildflowerSearch map]
[BONAP county map]
Discussion

The hybrid between Equisetum hyemale and E. laevigatum, E. × ferrissii, was mistaken for E. laevigatum by Schaffner and some subsequent authors. Although sterile, it exists outside the range of E. laevigatum, and apparently it is dispersed vegetatively (R.L. Hauke 1963). Perhaps it has persisted in some areas from a time when the parents were both there. Equisetum × ferrissii has been reported from Maine, New Hampshire, Rhode Island, South Dakota, and Vermont, but I have not seen specimens from those states.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 2. FNA vol. 2.
Parent taxa Equisetaceae > Equisetum > subg. Hippochaete Equisetaceae > Equisetum > subg. Equisetum
Sibling taxa
E. arvense, E. hyemale, E. laevigatum, E. palustre, E. pratense, E. ramosissimum, E. scirpoides, E. sylvaticum, E. telmateia, E. variegatum, E. ×ferrissii, E. ×litorale, E. ×mackaii, E. ×nelsonii
E. arvense, E. fluviatile, E. hyemale, E. laevigatum, E. palustre, E. pratense, E. ramosissimum, E. scirpoides, E. sylvaticum, E. telmateia, E. variegatum, E. ×litorale, E. ×mackaii, E. ×nelsonii
Synonyms E. limosum E. hyemale var. elatum, E. hyemale var. intermedium
Name authority Linnaeus: Sp. Pl. 2: 1062. (1753) Clute: Fern Bull. 12: 22. (1904)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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