Plant identification is a prerequisite to the science of botany and an invaluable skill for gardeners, farmers, foragers and naturalists. Plant identification lets you discern which wild herbs to pick, which seedlings to weed out of the garden, and which leaves to avoid brushing up against when hiking. Basic plant identification skills can start a backyard botanist on the road to a life-long study of the plant kingdom.
Basic plant identification is a necessary first step to any successful landscaping, gardening or farming venture, and a fundamental portal to the study of botany or environmental science. To the untrained or inexperienced eye, all green leafy things may look the same. Plant identification allowed early humans to encourage desirable food plants while discouraging unwanted plant competitors, thus sowing the seeds of agriculture and human development.
Dr. Steven Wolf writes, in his course notes on the History of Plant Taxonomy, that all cultures through history have learned to identify the plants growing in their area which are useful for food, clothing, shelter and construction, weaponry, and medicine. By 300 B.C., Theophrastos had written basic plant identification guides, distinguishing between classes of plants based on growth and flowering habits. Dioscoredes' Materia Medici written in the 1st century A.D. stood as the standard reference manual of plant identification until the 1400s, when advancements in printing and increased travel made plant identification books, particularly herbals listing useful plant medicines, increasingly popular.
The categories of plants outlined by Theophrastos--trees, shrubs, sub-shrubs and herbs--remains a valuable starting point in plant identification. Knowing a plant's general type allows you to check the appropriate reference materials for guidance as to which features to look to next.
Trees are further classified by deciduous (leaf-bearing) and coniferous (needle-bearing) types; shrubs, sub-shrubs and herbs by whether they are annuals (dying off after one year's growth) or perennials (returning each year from the same plant base), whether they are woody or non-woody, and whether they are flowering or non-flowering.
Individual plant identification is usually conducted by 'keying out' the plant in a botanical reference guide or in a garden or naturalist field guide. A plant identification is 'keyed out' by comparing the key features of the plant you are observing with those listed for each plant species or variety in the reference guide.
Key features for identification include branching habit and growing shape; leaf shape and placement; stem shape and elements like thorns or bark; flower timing, color, shape, and components; and root structure and form.
Some plants are poisonous, causing rashes or itches if touched or potentially serious illness if eaten. Many poisonous plants are similar in appearance to harmless landscape varieties. Poison ivy resembles pachysandra, while stinging nettles resembles garden mint. Do your initial plant identification by bringing your resource guides into the field, rather than the plant into your home. Only pick a specimen plant once you are confident that it is not harmful.