The North American Sylva, Volume 4, authored by Thomas Nuttall and published in 1842, is a significant continuation of the foundational work by François-André Michaux. This volume expands the botanical survey to include tree species from the western regions of North America, such as the Rocky Mountains, Oregon Territory, California, and other areas not covered in Michaux’s earlier volumes. Nuttall’s contributions are notable for their detailed descriptions and the inclusion of 122 finely colored plates that illustrate the leaves, flowers, and fruits of various tree species. These illustrations were created using the advanced technique of lithography, which was a progression from the copperplate engravings used in Michaux’s volumes.​

Nuttall’s work is distinguished by its comprehensive approach to documenting the diverse tree species across North America, particularly those in the western territories. His meticulous observations and detailed illustrations provide valuable insights into the botanical diversity of the continent. The volume serves as a crucial resource for understanding the distribution and characteristics of North American forest trees, especially those species that were previously undocumented in the eastern-focused studies of Michaux.​

The publication of Volume 4 marked a significant advancement in the field of botany, as it incorporated new scientific techniques and expanded the geographical scope of tree documentation. Nuttall’s dedication to exploring and recording the flora of the western United States contributed to a more comprehensive understanding of the continent’s botanical landscape. His work laid the groundwork for future botanical studies and remains a valuable reference for researchers and enthusiasts interested in North American forestry and natural history.​

The North American Sylva, Volume 4, by Thomas Nuttall, represents a pivotal addition to the study of North American trees. By extending the survey to include the western regions and employing advanced illustration techniques, Nuttall’s work complements and enhances the earlier volumes by Michaux. Together, these volumes provide a comprehensive overview of the continent’s forest trees, reflecting the rich botanical diversity and the evolving scientific methodologies of the 19th century.