Historical context
In the 17th century Biology were not a university subject. Practical knowledge of plants was confined to herbalists and farmers. A few people collected specimens of exotic plants for the gardens of stately homes.
Field guides & Herbals
Plants have always been used in medicine. Books intended to help people find and identify plants, with details of their supposed healing properties, appeared throughout the Medieval period. They were called ‘Herbals’. In 1636 an important Herbal by Gerard was published. Entries were usually not categorised, but listed in alphabetical order. Some ancient herbals categorised plants by the part of the plant used in medicine (root, leaf, etc) or classified by the organ of the human body it was supposed to heal.
Exotic plant collectors
In the Elizabethan period many formal gardens were laid out. John Tradescant the elder (d.1638) was a gardener to the aristocracy, and under Charles I became Keeper of His Majesty’s Gardens. When trade expeditions were made to Russia in 1618 and Algiers in 1621 he accompanied them as an official plant collector. His method was to purchase plants from nurseries and private gardens. From Algiers he brought back to England Gladiolus byzantinus, Syringa persica (lilac), narcissus, crocus, jasmine and many others. In 1626 he established his Botanical garden in South Lambeth.
His son, John Tradescant the younger (1608-62) travelled to Virginia in 1637, 1642 and 1654. His best known acquisition is Robinia pseudoacacia. By planting Platanus orientalis and Platanus occidentalis in his garden he came upon a cross-bred variety known today as the London Plane.
British field studies
In 1629 Thomas Johnson, an apothecary, travelled through twenty five English and Welsh counties in search of new plants. His intention, declared to Gerard in 1636, was "to travell over the most parts of this kingdom". Johnson fought as a Royalist, and was killed in 1644 at the siege of Basing House.
There were other apothecaries, physicians and clergymen who were interested in plants, and texts were published after Johnson’s death by William How (1620-1656) and Christopher Merrett (1614-1695), but none who travelled so widely in their searches as Thomas Johnson.