'Wild Fruit' (1991) is a collection of field notes and observations rescued from Thoreau's enormous backlog of unpublished illegible manuscripts and beautifully presented with illustrations and annotations.
To most people this book will be as boring as watching paint dry and the comparison is apt because Thoreau is almost doing just that. With painstaking detail this book layers tons of observations on all sorts of weedy and wild edible (fruit) plants through the year, commenting on their blooming season, taste, form and their history of domestication. This makes 'Wild Fruit' a kind of food-for-free augmented foraging guide of the Gutenberg age, informing you how to recognize plants, what can be eaten and when it is best eaten, and its place in history with quotes from 19Th century botanical sources as well as the 'classics'.
The fruits are listed by their consecutive period of fruitation throughout the year, an interesting way of organizing the material; appropriate but unusual when you are looking for a specific plant. (Did I ever tell you about 'Six Records of a Floating life' by Shen Fu?) This is not so much a guide as a database, a Xanadu machine for fieldnotes and perambulation about species and sometimes individual plants. You could very well imagine a online version of this book, and you can very well imagine this book as a model for a story telling approach to Boskoi and similar edible city Gmaps.
But this is Thoreau and what makes Wild Fruit essential reading as a precursor to the modern edible city / urban foraging revival is that his observations can at any moment issue and answer a philosophical question of the most basic nature: what do we know (we don't even know our own backyard) and how do we know it (hearsay and trust or direct observation and experimentation). The choice to be 'boring' is Thoreau's ultimate philosophical point.
The Preface by Bradley Dean is worthwhile.