There are no rules as to the type of trees that may be used as specimens, but they are typically selected for outstanding qualities, such as unusual or variegated foliage, spectacular flowering, or beautiful autumnal colour.
Exotic tree varieties may be rare or expensive; these may be planted as status symbols. An example would be an exotic Fir or spruce planted in an Australian garden, or a banana or other tropical tree growing in a container garden in New York.
Qualities gardeners may use to select specimen trees
- Beautifully shaped trees - called a tree's "form"
- Interesting style of growing branches - called "habit" - "weeping" trees are an example
- Old or ancient trees
- Coloured and/or variegeted (two-toned) leaves
- Trees of a certain height
- Autumnal colour
- Floral or fruit display
- Edible fruit
- Rare species or variety
- Shade or shelter in a particular spot
- Provide a focal point in a park, set off a house or outbuilding
Plants used for decoration or as special features in a house or garden are just as hard to define as ornamental trees, probably because this is a matter of personal taste. Certainly, most people think of that which is showy or unusual as being ornamental, but there is nothing which says that functional plants (such as fruiting plants or cash crops) cannot be used as ornamentals as well. Grapes grown over an arbour, for example, make a definite ornamental statement, notwithstanding that there are hybrids and cultivars which are called "ornamental grapes" and which have been developed specifically for decoration. Similar statements could be made for peppers and cabbages; in fact, all sorts of herbs, fruits and vegetables may be grown as ornamentals. Even inhospital, thorny plants can be used as striking decoration.