Equisetum hyemale subsp. affine
(Engelm.) Calder & Roy L. Taylor
[Equisetum affine Rydb., more, Equisetum hyemale var. affine (Engelm.) A. A. Eat., Equisetum hyemale var. californicum Milde, Equisetum hyemale var. elatum (Engelm.) Morton, Equisetum hyemale var. intermedium A.A.Eaton, Equisetum hyemale var. pseudohyemale (Farw.) Morton, Equisetum hyemale var. robustum (A. Br.) A. A. Eat., Equisetum praealtum Raf., Equisetum robustum A. Br. ex Engelm., Hippochaete hyemalis f. affinis (Engelm.) Satou]
Perennial herbaceous fern ally 18 cm - 2.2 m tall Spores: green, spheric, and released from lengthwise slit in spore sacs (sporangia). Stems: one to several, erect, straight, unbranched, green (even during winter), often robust, round with hollow center and fourteen to fifty lengthwise rows of ridges and alternating valleys on outside. The stem joints have distinct nodes, and the stomates are sunken and arranged in single lines on each side of the stem valleys. Sheaths: brown to gray with dark ring (girdle) at base, 4.5 - 17 mm long, 3.5 - 18 mm wide, square in face view. The sheaths are actually small, fused, whorls of leaves. Sheath teeth: fourteen to fifty, usually shed along a particular darkish line (articulation line) or sometimes more persistent.
Similar species: Equisetum hyemale ssp. affine is most similar to E. laevigatum and E. variegatum, but both those species lack the dark girdle around all the stem sheaths, their sheaths are more elongate, and they often have less teeth per sheath (only up to twelve in E. variegatum). Equisetum laevigatum further differs by having a blunt tip on the cone even if it abruptly appears to come to a point. The hybrid between E. hyemale and E. laevigatum is E. x ferrissii, which differs from E. hyemale by having only up to 32 teeth per sheath, the sheaths are longer than wide, and the spores are white and misshapen. The hybrid with E. variegatum, E. x mackaii, can be differentiated because it has only up to about sixteen teeth per sheath, the sheaths are elongate (longer than wide), the teeth are persistent, and the spores are white and misshapen. The typical subspecies, E. hyemale ssp. hyemale, only occurs in Europe and Asia.
Habitat and ecology: Common, often along moist slopes and embankments as well as in pastures, degraded prairies, or along roadsides.
Occurence in the Chicago region: native
Notes: This plant often produces large colonies of green stems that persist through the winter. As in other members of this genus, E. hyemale ssp. affine is able to absorb and deposit silica in its stems. Apparently it is due to the harsh silica in the stems that pioneers used the plants to scour pots and pans. The genus Equisetum (the only living members of the Equisetaceae family) has been studied often as a means to understand the evolution of vascular plants. They are often also used to interpret fossil plants in a group called the sphenopsids, which first appeared in the Devonian Period (about 360 to 415 million years ago). At that time, the plants were treelike and reached sizes of well over 10 m tall and even 1 m in diameter. The group reached a point of high diversity in the Carboniferous (300 to 360 million years ago) when the majority of our coal deposits started forming from these and other plants. Today only these small plants (up to about 2 m tall and under 4 cm diameter in our largest species) survive from this once land-dominating group.
Etymology: Equisetum comes from the Latin words equus, meaning horse, and saeta, meaning bristle. Hyemale (or Hiemale), is from the Latin hiems, meaning winter or winter flowering. Affine means related or similar.