Cactus: what one should know?
Having no attractive leaves, these plants have usually conspicuous flowers. Epiphyllum, the orchid cactus, is the first with its fragrant flowers that may grow up to 8 inches across.
One more distinctive characteristic peculiar to every cactus plant, but absent in all species of all other families, is its “isolation”. This is the spine cushion or areole, all cacti have areoles. As far as these areoles differ in structure according to different kinds of cacti, this is one way of distinguishing one cactus plant from another.
There is one plant family which is often confused for the cactus family: this is the euphorbia family which includes such plants as Cow’s Horn Cactus, African Milk Bush and Crown of Thorns (E. milii). All these plants have spines, green stems and few or no leaves at all, but they do not have areoles.
If you are still have doubts whether you have a euphorbia or a cactus, make a small cut in an insignificant place. If you notice the milky white and sticky sap, then you have a euphorbia, while cactus sap is clear and watery.