Abraham Léo Errera (4 September 1858 in Laeken – 6 August 1905 in Brussels) was a Belgian botanist, known for his research in the field of plant physiology. He worked at the Free University of Brussels in 1883 as an associate and in 1890 a full professor of botany. In addition, he was actively involved in Jewish affairs.
After receiving his liberal arts degree at the Université Libre de Bruxelles (1874), his focus turned to natural sciences, and in 1879 obtained his doctorate in botanical science. He then travelled to Germany, where he furthered his education at the Universities of Strasbourg, Bonn, and Würzburg. In Strasbourg, he conducted research in the laboratories of Anton de Bary and Felix Hoppe-Seyler. At Würzburg, he studied plant physiology under Julius von Sachs.
Following his return to Brussels, he founded the Laboratoire d'Anatomie et de Physiologie Végétales. This laboratory eventually featured facilities for microscopy and chemistry, a greenhouse, a photography studio, a sterilization chamber, a thermostatic chamber and a darkroom for spectroscopy and polarimetry.
He is credited with discovering the presence of glycogen in plants and fungi (amylopectin) through the use of sophisticated techniques. He later employed these techniques to detect alkaloids in plants.