Equus (genus)
Equus is a genus of mammals in the family Equidae, which includes horses, donkeys, and zebras. Within Equidae, "Equus" is the only recognized extant genus, comprising seven living species. The term equine refers to any member of this genus, including horses. Like Equidae more broadly, "Equus" has numerous extinct species known only from fossils. The genus most likely originated in North America and spread quickly to the Old World. Equines are odd-toed ungulates with slender legs, long heads, relatively long necks, manes (erect in most subspecies), and long tails. All species are herbivorous, and mostly grazers, with simpler digestive systems than ruminants, but able to subsist on lower-quality vegetation.
Equisetum
The genus "Equisetum" as a whole, while concentrated in the non-tropical northern hemisphere, is near-cosmopolitan, being absent only from Antarctica, though they are not known to be native to Australia, New Zealand nor the islands of the Pacific. They are most common in northern North America (Canada and the northernmost United States), where the genus is represented by nine species ("arvense", "fluviatile", "palustre", "pratense", "sylvaticum", "hyemale", "laevigatum", "scirpoides", and "variegatum"). Only four ("bogotense", "giganteum", "myriochaetum", and "ramosissimum") of the fifteen species are known to be native south of the Equator. They are perennial plants, herbaceous and dying back in winter as most temperate species, or evergreen as most tropical species and the temperate species rough horsetail ("E. hyemale"), branched horsetail ("E. ramosissimum"), dwarf horsetail ("E. scirpoides") and variegated horsetail ("E. variegatum"). They typically grow 0.2–1.5 m tall, though the "giant horsetails" are recorded to grow as high as 2.5 m (northern giant horsetail, "E. telmateia"), 5 m (southern giant horsetail, "E. giganteum") or 8 m (Mexican giant horsetail, "E. myriochaetum"), and allegedly even more.