Pinax rerum naturalium Britannicarum was a replacement for a proposed revised edition of William How’s Phytologia Britannica of 1650. The plan to produce a revised edition of this catalogue of British flora, fauna and fossils had fallen through at How’s death in 1656 and so Merret and fellow physician John Dale were commissioned to publish a new work.

Dale, who was to write the botanical section, died soon after and Merret decided to finish the work himself. Using unpublished manuscripts, his own observations made during excursions in the north of England and 800 unused engravings commissioned by Thomas Johnson for his revised edition of Gerard’s Herball, Merret set about preparing the text.

Most of the first impression, printed in 1666, was lost during the Great Fire of London, leaving those that survived to be included with the second impression, dated the following year. Merrett had little botanical knowledge and Pinax contains many inaccuracies on the subject. This led him to disown the edition and begin preparing a revised one, but nothing materialised.

Despite its botanical failings, the work did include some of the first comprehensive lists of British birds and butterflies and is among the first works by an English writer to discuss the organic origin of fossils.