Robert Hagelstein (May 16, 1870 – Oct. 20, 1945) was a multidisciplinary businessman, scientist, and microscopy expert who served for fifteen years as the Honorary Curator of Myxomycetes at the New York Botanical Garden.

He is known for his work in algae and slime mold specimen collection and curation, and for making hands-on learning materials widely available to student and amateur scientists.

[2] After graduating from high school, Hagelstein initially chose a career track in business with the J. and D. Lehman Company glove manufacturer in New York City.

[2] Over the years the microscopy department declined and many of its most active participants, including Hagelstein, resumed their work at the New York Microscopical Society during World War One.

[1] The work ethic and eye for detail that Hagelstein had cultivated during his years as a businessman made him a successful and effective curator for the New York Botanical Garden.

[4] He contributed an extensive photomicrography record to the New York Botanical Garden collection and regularly published his findings to advance the knowledge of his specialized field.

[1] On January 11, 1941, the Cryptogamic Herbarium of the New York Botanical Garden was officially opened, and included a special room devoted to Hagelstein's diatom and myxomycetes collections.

[2] After his death, the New York Botanical Garden Library received and continues to maintain a collection, entitled "The Robert Hagelstein Records, 1904–1945", of his personal correspondence, notebooks, manuscripts, photographs, and publications.