Seed of the Week: Small Prostrate Sandmat

Our mystery seeds stored by ants last week have a few common names, but let’s use small prostrate sandmat. The scientific name is Chamaesyce prostrata (sometimes Euphorbia prostrata).

prostrate-sandmatHere’s another look at the wrinkly seeds (photograph by Carole Ritchie, hosted by the USDA-NRCS PLANTS Database.)

spurge-cotyledonsIt is not uncommon to find germinating seeds near ant nests.

spurge-seedlingsThe plants are quite small and low growing.

spurge-plantAnother common name is ground spurge.

spurge-ant-flowerThe sandmats or spurges have small, somewhat oddly-structured flowers that attract ants. (more about Euphorbia flower structures). At least some of the sandmats are likely pollinated by ants (see post at Wild About Ants).

Back to the mystery post, why would ants want to store the sandmat seeds?

It turns out the sandmat seeds have a structure that serves as food for ants called a caruncle. The ants bring the seeds back to the nest, pull off the caruncle and eat it, and then discard the rest. (A more generalized term for this kind of structure on a seed is an elaiosome. ) That is why sandmat often grows around ant nests.

Do sandmats or ground spurges grow where you live? What common name do you use?


  1. Nathan Taylor

    Actually, Euphorbia sect. Anisophyllum (the group also known as Chamaesyce) is one of the few Euphorbia groups that lack caruncles. It is even one of their defining characteristics along with C4 photosynthesis, dorsi-ventral stems, and sympodial branching. Also, the second to last photo is Euphorbia serpens and not E. prostrata. The seedlings in the third photo are also not E. prostrata as they lack hairs on the stems. I can’t tell what they are though. I can’t ID the other seedling photo.

  2. Roberta

    Cool. Thank you for sharing your expertise. As an entomologist, I only dabble in botany I’m afraid.

  3. Nathan Taylor

    No problem. I know a decent amount about the plants, but not much about the insects, so I’m glad you’re studying them.

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