The Arnold Arboretum has two wonderful clusters of honey locust trees (genus Gleditsia); one on the west flank of Peters Hill, and the other appropriately embedded in the legume (pea family) collection next to Rehder Pond. Now is a great time to literally see the (pea pod-like) fruits of these trees’ labors, on the ground or hanging from the otherwise naked branches. Pictured below are the fruits and seeds of the Caspian honey locust (Gleditsia caspica, 272-72*A). If you are in the neighborhood, split open one of the pods to discover a gooey sweet mucilaginous substance (upper right; hence the name honey locust) and a series of chambers, each filled with a single hard-shelled brown seed (lower right).
At the Arboretum, we have great representation of the dozen or so species now extant in Asia, North America, and South America. The biogeographic distribution of this genus is classic disjunct: eastern Asia–eastern North America, with an evolutionary center of origin in eastern Asia, and a migratory journey across the former Bering land bridge millions of years ago to eventually give rise to the two North American species, Gleditsia tricanthos (honey locust) and Gleditsia aquatica (water or swamp locust).
Petty grievance: The huge clusters of thorns on the trunks and branches of Gleditsia trees are magnificent (see Post from the Collections, January 31, 2016; Armed and Dangerous Plants in the Arnold Arboretum). The American honey locust (Gleditsia tricanthos) is a common street tree, but sadly with cultivars bereft of the normally murderous thorns and messy fruits. What’s the point of such stripped-down cultivars?! At the Arboretum, our wild-collected specimens are truly armed and dangerous, and as messy as can be!