Branched-chain sugars and sugar alcohols are unusual, but perhaps widespread, plant constituents whose associated biochemistry and function are poorly understood. Herein we show that one such sugar alcohol, hamamelitoi (2-C-hydroxymethyl-D-ribitol), does occur in leaves of many different species often in very high amounts. Hamamelitol levels were quantitated by an isotope dilution assay we developed with a detection limit of about 15 nmol per g fresh weight, and its identity was verified using electrospray ionization mass spectrometry. The taxonomic distribution of hamamelitol was disjunct: hamamelitol was present in species of distantly related orders such as Laurales, Fabales, and Primulales, but was not necessarily present in different genera of the same family. Species with high leaf levels of carboxyarabinitol (2-C-hydroxymethyl-D-ribonic acid) generally have low hamamelitol levels. Leaves of Hedera helix L. contain the most hamamelitol of any species examined, with levels comparable to those of sucrose. The youngest leaves of H. helix accumulated the most hamametitol, about 11 gmol per g fresh weight. Growth of H. helix with periodic sub-freezing temperatures did not induce further accumulation of leaf hamamelitol. Hamamelitol levels were also high in leaf petioles of H. helix, which indicates that this sugar alcohol may be translocatable, Further, the mass spectrometry analysis indicates that a non-covalent dimer of hamamelitol may be more prevalent in vivo than is the monomeric form.