Fertile Stems of The Field Horsetail

Strobilus of Equisetum arvense

Horsetails are represented by only one extant genus (Equisetum) but many extinct species are represented in the fossils record. Taxonomically, they are placed in the class Equisetopsid (Sphenopsida) order Equisetales and family Equisetaceae. Equisetopsids first appeared in the Devonian period but, attained their maximum diversity during the Carboniferous. From the Carboniferous to the present day, the group has experienced a gradual decline to where today just 15 species are recognised (Taylor et al. (eds), 2009 Biology and Evolution of Fossil Plants pp. 329-382). They are characterised as having whorled, gapped stems and connate, whorled leaves. Features of their spermatazoids group them with ferns, with their closest phylogenetic relative being the Marattiopsids (Smith et al., 2006 Taxon 55 (3) pp. 705–731)

Vegetative stem of Equisetum arvense

In Ireland, the most abundant horsetail species is the Field or Common Horsetail (Equisetum arvense). It favours wet soil conditions and is most common on or near river banks, but can establish on arable land becoming a troublesome weed.

At this time of the year, the green stems of E. arvense are nowhere to be seen, having died away during the winter. Instead, pinkish-brown stems are visable and will be until June. These are the fertile stems of the horsetail. The cone at the top of the stem (the strobili) is comprised of peltate sporangiophores that bear the sporanhia.