Equisetum hyemale; The Rough Horsetail is common on Iceland. It grows both in lowland and highland regions, where ever conditions are reasonably favorable for plant growth. However, it is not a bog plant like some other horseteils. This horsetail can easily be distinguished from others: it is a totally unbranched-stem species which are far thicker in than any other species. I have also noticed that this plant is used in revegetation programmes on barren wind-eroded land around Mývatn. The Icelandic name is Eski. Similar species can be identifies by the following characteristics:
- E. arvense, field horsetail: the sporangial cones appear very early in spring on colorless stems before the green stems. The green stems typically have side branches pointed upwards.
- E. pratense, shady horsetail: characteristic are the horizontal, even drooping downwards of the lateral branches. The sporangial cones, however, appear on at first on top of unbranched main stems which form the lateral branches later as the spores mature.
- E. palustre: marsh horsetail: short side branches, terminal cones not pointed, about 13 dental points on stem-sheaths.
- E. fluviatile: water horsetail: no side branches, terminal cones not pointed, about 14 dental points on stem-sheaths.
- E. variegatum: variegated horsetail: no side branches, terminal cones pointed, about 5-8 dental points on stem-sheaths.
- E. hyemale: rough horsetail: no side branches, about 20 dental points on stem-sheath - but very tiny: the sheaths seems almost round. Much thicker stems than any other horsetail on Iceland.