Dr. Lew Feldman, Garden Director
Next time you are in the Garden and walking past Southern African Area, stop for a moment and look for the Lampranthus, a genus of plants that have unusually large, bright flowers that appear in summer, and frequently cover the plants entirely. Lampranthus can be distinguished by the large seed capsules (= fruits) which enclose several to many seeds.
Part of the evolutionary success of this genus is the way that it protects its seeds from predation, keeping them enclosed in the fruit, waiting until the right environmental conditions exist to release the seeds. For Lampranthus, the “right” environmental condition is the arrival of soaking rain, which supports seed germination and seedling establishment. But how does the Lampranthus “know” when such a rain arrives and thus when to release the seeds from enclosure by the fruit?
If you look carefully at the fruit you will notice circularly arranged, triangular flaps, under which are the seeds, as pictured below.
Although the cells making up the flaps are no longer alive, when they become wet they behave as if they were still alive, resulting in the flaps folding back, exposing the seeds to the environment.
But the function of the rain goes beyond causing the flaps to pull apart. Depending on the velocity and size of the raindrops, as the drops strike the seeds, the seeds are ejected from the fruit and can travel a considerable distance, thereby dispersing them away from the parent plant.