He took art classes in
Breslau, qualifying as an art teacher in 1881. He furthered his studies in
Munich and
Paris, where his interest in
natural sciences grew. He subsequently moved to
Zurich in 1892 in order to study
geology. In the latter part of the 1890s, he was invited by botanist
Melchior Treub to Java as an illustrator. On Java, along with his artistic duties, he collected regional botanical specimens and conducted investigations of the island's mosses. Fleischer distributed several
exsiccatae, among them
Musci frondosi Archipelagi Indici exsiccati and – together with
Carl Friedrich Warnstorf –
Bryotheca Europaea Meridionalis. During his time spent in the
Dutch East Indies, he also learned the technique of creating
batik prints from
vegetable dyes. After several years on Java, he traveled to
New Guinea, the
Bismarck Archipelago,
Australia,
New Zealand and
South America, prior to returning to Germany in 1903. From 1908 to 1913, he revisited
Maritime Southeast Asia, where he collected mostly
bryophytes but also
orchids and
fungi on Java. In 1914 he began work at the botanical museum in
Berlin and three years later, he was appointed a professor of botany at the
University of Berlin. In 1925 he traveled to the
Canary Islands in order to paint and to study the regions' mosses. During the following year, he relocated to
The Hague, and in 1927 he returned to the Canaries with his second wife, P.G. Haigton. After his death in 1930, his private collections and library were purchased by an
antiquarian in
Leipzig. ==Gallery==