In February, while hiking with friends along Abbott’s Lagoon Trail at Point Reyes National Seashore in California, we found some horned searocket (Cakile maritima) plants in bloom. The plants also had siliques – hard, corky, dehiscent fruits found in members of the Mustard Family (Brassicaceae). Chris, the botanist in our group, noted that horned searocket siliques have heteromorphic seeds. Even though I previously did a post on this introduced, annual, halophyte (08-20-18 “Horned Searocket”), here was something I had not realized before.
Seed heteromorphism is a reproductive strategy characterized by simultaneous production of multiple seed types. Germination of seeds is important for establishing seedlings. Structural and physiological differences (morphology, ripening, dormancy, size, dispersal, germination time, for example) allow plants to germinate in more than one type of environment, disperse differently or help when environmental conditions are uncertain. Often seed heteromorphs have a “colonizer” morph that is optimized for dispersal and a “maintainer” morph optimized for local establishment. Horned searocket is an example of a plant with seed heteromorphism, although many other plants show this same trait, expressed in different ways.
Each horned searocket, also commonly called European searocket, silique has two chambers, each usually containing one seed. The upper section releases seeds that have good floating ability and inhibition of germination during flotation enabling long-distance dispersal of the species by sea currents. The lower portion of the silique remains attached to the parent and drops its seeds under or near the parent plant, thus maintaining the original colony. This strategy is obviously successful because horned searocket has spread to most of the world’s coastal regions.
Cordazzo et al (2006) in Brazilian Journal of Botany and Debez et al (2018) in Physiologia Plantarum did research specifically on horned searocket seed heteromorphism.