This is partially true but do not rely on this as a guide. A sucker will originate from the base of the plant or further away, have pale green leaves, green stems and few thorns. They look totally different to roses and are not common now. Some people tend to worry too much about suckers – we have had climbing roses returned to us after two or three years because, according to the customer, they just send out suckers from the base which they pull off and the rose fails to climb. After inspecting the plants in question, the so-called ‘suckers’ are actually the rose trying to climb!