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.
Equisetaceae
All living horsetails are placed in the genus "Equisetum". But there are some fossil species that are not assignable to the modern genus. "Equisetites" is a "wastebin taxon" uniting all sorts of large horsetails from the Mesozoic; it is almost certainly paraphyletic and would probably warrant being subsumed in "Equisetum". But while some of the species placed there are likely to be ancestral to the modern horsetails, there have been reports of secondary growth in other "Equisetites", and these probably represent a distinct and now-extinct horsetail lineage. "Equicalastrobus" is the name given to fossil horsetail strobili, which probably mostly or completely belong to the (sterile) plants placed in "Equisetites".