A variety is a plant that is different in some way, and continues to be different, from the rest of the species but is not different enough for it to be classified as a new species or as a sub-species. This difference will usually be bigger than those of a form; a form will have one or more small differences, for example, different coloured flowers, lack of thorns, variegation or different coloured leaves. These variations come about by natural evolutionary process to which most plants are subject. However, a taxonomist can use his own judgement as to at what rank he wants to recognize a different plant. What one taxonomist will call a variety, another will call just a form, or will decide not to recognize as being distinct.