Alexander Zahlbruckner was an Austrian-Hungarian botanist who specialized in the study of lichens. Johann Babtist Zahlbruckner, an earlier Austrian botanist, was his grandfather.
From 1878 to 1883 he studied at the University of Vienna, where his instructors included Anton Kerner von Marilaun and Julius Wiesner. Afterwards, he served as a voluntary assistant to Günther Beck von Mannagetta und Lerchenau at the Naturhistorisches Museum in Vienna, where he later attained the titles of assistant curator, curator and head curator. From 1918 until his retirement in 1922, he was director of the museum's botany department. From 1920, he was member of the Hungarian Academy of Sciences In retirement, he continued his studies in the field of lichenology.
In 1905 he served as general secretary of the International Botanical Congress, held in Vienna. Zahlbruckner is known for publication of Catalogus lichenum universalis, a catalog of all published names of lichens, issued in ten volumes from 1922 up until 1940. He also published regional works on lichen-forming fungi of central Africa, South America, China, Easter Island, Juan Fernández Islands, Dalmatia, Formosa, Japan, Java and Samoa.