The overall size and shape of an organism. Descriptions such as ‘trees’, ‘shrubs’, and ‘herbs’ are frequently used to characterize the general appearance of the vegetation of a region. Moreover, plant physiognomy can be broadly correlated with environmental conditions, so that regions of the world with similar climates tend to have a dominant vegetation of similar life forms. Various attempts have been made to refine this approach by defining physiognomic categories, or life forms, most notably by the Danish ecologist Christen Raunkiaer (1876–1960). His system of classifying life forms is based on the way in which plants survive harsh conditions, particularly the position of their perennating (or overwintering) buds in relation to the soil surface. He proposed five classes: therophytes (annual plants); geophytes (plants that produce underground perennating organs); hemicryptophytes (herbaceous perennials); chamaephytes (small shrubs); and phanerophytes (large shrubs and trees).