Horse
The horse adapted to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not. Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during the Tertiary period. In the past, this order contained 14 families, but only three—Equidae (the horse and related species), Tapiridae (the tapir), and Rhinocerotidae (the rhinoceroses)—have survived to the present day.
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.