A horticultural flora, also known as a garden flora, is a plant identification aid structured in the same way as a native plants flora. It serves the same purpose: to facilitate plant identification; however, it only includes plants that are under cultivation as ornamental plants growing within the prescribed climate zone or region. Traditionally published in book form, often in several volumes, such floras are increasingly likely to be produced as websites or CD ROMs.
Scope and contents
Horticultural floras include both cultigens (plants deliberately altered in some way by human activity) and those wild plants brought directly into cultivation that do not have cultigen names. They might also include colour images and useful information specific to the zone or region including:
- historical details about outstanding public and private cultivated plant collections
- exceptional trees (age, history, rarity, size etc.)
- prominent nurserymen and plant breeders
- references to the taxonomic and other literature on the plant groups
- easy "spotting" or "field" characters useful for quick identification
- notes on ecology (especially the potential of plants to naturalise and become invasive)
- horticultural history of introduction
Written by a professional plant taxonomist or plantsperson, a horticultural flora assists clarification of scientific and common names, the identification of plant characteristics that occur in cultivated plants that are additional to those in wild counterparts, and descriptions of cultivars.
Although horticultural floras may include a range of food plants, their emphasis is generally on ornamental plants and so these floras are sometimes referred to as "garden floras." Increasingly they provide data for sustainable landscaping, such as:
- drought tolerance and irrigation needs
- food sources of native and migratory bird and butterfly species
- companion planting
- invasive species notation
- local habitat restoration aspects.
Published horticultural floras
Numerous encyclopaedic listings of cultivated plants have been compiled but only four substantial horticultural floras have ever been produced, these being for: North America; Europe;  South-eastern Australia, Hawaii and the tropics.
- Bailey, Liberty Hyde (1924), Manual of Cultivated Plants: A flora for the identification of the most common or significant species of plants grown in the continental United States and Canada, New York: Macmillan
- Cullen, James; Knees, Sabina; Cubey, H Suzanne (eds) (2011), The European Garden Flora: A manual for the identification of plants cultivated in Europe, both out-of-doors and under glass. Vols 1–5, Cambridge, UK: Cambridge University Press, ISBN 9780521761673 (5 volume set)
- Cullen, James; Knees, Sabina; Cubey, H Suzanne (eds) (2000), The European Garden Flora: A manual for the identification of plants cultivated in Europe, both out-of-doors and under glass. Vol 6, Cambridge, UK: Cambridge University Press, ISBN 0521420970 (out of print)
- Spencer, Roger (ed) (1995–2000), Horticultural Flora of South-eastern Australia: The Identification of Garden & Cultivated Plants, Sydney, Australia: University of New South Wales Press, ISBN 0 86840 167 6 (set)
- Staples, George W; Herbst, Derral R (2005), A Tropical Garden Flora: Plants cultivated in the Hawaiian Islands and other tropical places, Honolulu: Bishop Museum Press/Mutual Pub Co, ISBN 1581780397
- Rehder, Alfred (1987 (New edition of Second Revised Edition)), Manual of Cultivated Trees and Shrubs Hardy in North America, Portland, Oregon: Timber Press, ISBN 0-931146-00-3
- Ritter, Matt (2011), A Californian's Guide to the Trees Among Us, California: Heydey, ISBN 978-1-59714-147-5