Plant Story -- Osage-Orange and the Animals of the Pleistocene

Osage-oranges
 on the ground

Osage-orange, Maclura pomifera, is a tree endemic to (native only in) North American. Its range. when Europeans first encountered it, was small: the area where Arkansas, Texas and Oklahoma meet. Its habitat is described as woods, forest edges and streams. Widespread planting of Osage-orange for fences in the 1850s-1870s has greatly expanded its distribution.

I talked about Osage-orange's interesting wood previously (link). But Osage-orange has memorable fruits. See Osage-orange fruit They are bigger than oranges. The outer rind is warty. Inside it is more solid than an orange, with a row of small seeds. (Gray's Manual of Botany calls the fruits "disappointingly dry and hard" inside). Not much of anything eats them. People don’t eat them, some horses like them, deer eat a few and determined squirrels will tear them open and eat the seeds, but still the big fruits pile up at the base of the tree. 

Mostly we don't think about what we see and ask "why?" But why does Osage-orange make a huge fruit? Plants are rooted. To get to new areas, something (wind, water, an animal) has to carry the seeds away. Osage-orange fruits seem horribly inefficient at dispersing the plant. 


The current answer is: the fruits evolved to be eaten by animals that have gone extinct.