These books deal mostly with the flora of northeastern North America.

General Floras

Gray's Manual of Botany. Still one of the great standard references for the flora of northeastern North America. It has been through eight editions, of which seven are out of copyright. The titles of the various editions vary, and no one of them seems actually to be called Gray's Manual of Botany, but that is the title by which botanists usually refer to it.

Seventh edition. Gray's New Manual of Botany (Seventh Edition—Illustrated). A Handbook of the Flowering Plants and Ferns of the Central and Northeastern United States and Adjacent Canada. Rearranged and Extensively Revised by Benjamin Lincoln Robinson and Merritt Lyndon Fernald. This is the edition best used for reference today.

An Illustrated Flora of the Northern United States, Canada, and the British Possessions, by Nathaniel Lord Britton and Hon. Addison Brown. —This is the other standard reference for northeastern North America.

Vol. I  (second edition,1913).
Vol. I  (first edition, 1896).

Vol. II (second edition, 1913).
Vol. II (first edition, 1897).

Vol. III (second edition, 1913).
Vol. III (first edition, 1898).

Manual of the Flora of the Northern States and Canada
by Nathaniel Lord Britton. Third edition, 1907. Based on Britton and Brown's Illustrated Flora.

A Brief Flora of the Eastern United States. By W. Nevin Geddes, A.M., Ph.D., 1903. Bound with E. F. Andrews' Botany All the Year Round.

Flora Atlantica. Descriptive Botany; Being a Succinct Analytical Flora, including all the plants growing in the United States from the Atlantic coast to the Mississippi River. By Alphonso Wood, A.M., 1879.

The American Botanist and Florist: Including Lessons in the Structure, Life, and Growth of Plants; Together with a Simple Analytical Flora, descriptive of the native and cultivated plants growing in the Atlantic division of the American Union. By Alphonso Wood, A.M., 1873. (Useful for its descriptions of plants commonly cultivated in 1873.)

The North American Sylva, or a Description of the Forest Trees of the United States, Canada and Nova Scotia, considered particularly with respect to their use in the Arts, and their introduction into Commerce; to which is added a description of the most useful of the European forest trees. Illustrated by 156 coloured engravings. Translated from the French of F. Andrew Michaux, member of the American Philosophical Society of Philadelphia, &c., &c. Paris: C. D'Hautel, 1818-1819. —Gorgeous colored engravings, generally well scanned.
Vol. I

Vol. II.

Vol. III

Sketches Towards a Hortus Botanicus Americanus; or, Coloured Plates (with a catalogue and concise and familiar descriptions of many species) of new and valuable plants of the West Indies and North and South America. Also of several others, natives of Africa and the East Indies: arranged after the Linnaean System. With a concise and comprehensive glossary of terms, prefixed, and a general index. By W. J. Titford, M. D. London: Printed for the author, 1811. —The engraved ornamental title page leaves out "Sketches Towards a," and gives the place and date of publication as "New York 1810." It is followed by the standard boilerplate American copyright notice of the period ("Be it remembered..."). Many fine colored engravings; the scans are mostly good.

Pittsburgh and Pennsylvania

Flora of Pennsylvania, by Thomas Conrad Porter, D.D., Ll.D., 1903.

Pennsylvania Trees. By Joseph S. Illick, 1919.

A Preliminary List of the Vascular Flora of Allegheny County, Pennsylvania, by John A. Shafer, Ph.G., 1901.

Check List of the Vascular Flora of Allegheny County, Pennsylvania. By L. K. Henry and W. E. Buker. In Trillia: Proceedings of the Botanical Society of Western Pennsylvania. This is an updated (published 1951) and expanded version of Shafer’s list above.

Handbook of the Flora of Philadelphia and Vicinity. By Ida A. Keller and Stewardson Brown, 1905.