From microscopic single-celled species to giant seaweeds many meters long, algae are diverse and ancient organisms that can be found in virtually every ecosystem on earth. For millions of years algae have exerted profound effects on our planet. As primary producers algae provide food and shelter for many organisms as well as provide a significant percent of the oxygen we breathe. Algae are locally important water quality indicators and globally important sequesters of carbon dioxide, the major greenhouse gas involved in global climate change.

The New York Botanical Garden Herbarium includes about 150,000 algae specimens. Approximately half of these are from North America. Of the remaining half, specimens collected in the Caribbean region and Central and South America predominate. The specimens have been collected over the past 150 years by a number of phycologists, but most notably by T. F. Allen, F. S. Collins, M. A. Howe, and R. D. Wood. More recently, specimens that document the research of P. I. Karol have been added to the collection. The vast majority of specimens held were collected before 1950.

The algal collection was built primarily by Marshall Avery Howe, phycologist and Assistant Director of the New York Botanical Garden, whose years at the Garden spanned 1901 to 1936. Howe collected more than 35,000 specimens of algae in eastern North America, Panama, and the West Indies. Howe was instrumental in obtaining the herbaria of Timothy Field Allen and Frank Shipley Collins, the most important private algal herbaria of the day. Allen was the leading American student of the Charophyceae during the late 1800s, and he built a collection of approximately 4000 specimens from North and South America, Asia, and Europe. This herbarium was used extensively in the preparation of the monumental two-volume work, A Revision of the Characeae, by Richard D. Wood and Kozo Imahori. In 1978, the Garden received Wood's charophyte herbarium (ca. 7000 specimens), and together the Allen and Wood collections make the Garden's charophyte herbarium one of the finest in the world. Another area of taxonomic emphasis are coralline algae of the Caribbean region, Howe's particular area of research interest.