Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
Equus publicus a property value of more than 100,000 denarii or else inheritance, but the equus publicus was only attainable by way of inheritance from a father. In imperial times, after the reforms of Augustus, the status could be granted by an emperor, along with inheritance from a father. Equus publicus The Equus publicus (literally "horse bought by the commonwealth") was an honourable status in ancient Rome, granting its holder a military horse paid for by the state, along with the cost of its fodder for its whole life. The money for the horse was called "aes equestre", whilst the annual money