Yesterday's general post about seed dispersal by ants reminded me of a specific example in my own yard.
These tiny seedlings started to germinate in the soil around a Solenopsis xyloni nest.
It didn't take too long to figure out the plants were ground spurge, Chamaesyce prostrata. Another common name is sandmat. Ground spurge is a native annual that is usually considered to be a weed.
Why are seedlings growing on ant pilings significant?
The seeds of spurges are known to have elaiosomes, and in fact the elaiosomes are given a different name. The special structures on seeds that serves as food for ants in spurges are called caruncles. It's easy to remember if you realize it comes from the Latin caruncula, which means wart.
Alex Wild has an excellent series of photographs of Formica ants with the seeds of the invasive spurge, leafy spurge.
It turns out that ants are known to disperse and accidentally plant the seeds of a number of different species of spurge. In fact, ants may have another close association with spurges, but let's save that one for the next post.
For more information:
Robert W. Pemberton and Delilah W. Irving. (1990). Elaiosomes on Weed Seeds and the Potential for Myrmecochory in Naturalized Plants. Weed Science. 38(6): 615-619.
John Eastman also talks about spurges in Book of Field & Roadside: Open-Country Weeds, Trees, and Wildflowers of Eastern North America.