Seed dispersal is crucial to the success of a species and its population. Most plants rely on gravity for seed dispersal, but some plants such as hairy bittercress, Cardamine hirsuta, use projectile mechanisms to spread seeds farther than a gravity-bound mechanism would result in.
C. hirsuta is a Brassicaceae noted in most areas of America, states in the center of North America due to insufficient moisture. This is an introduced/ invasive species from Europe and Asia with transfer to the American continent most-likely from being carried on ships by hitch-hiking on clothing and in vessels. Often-times, the reason a plant becomes invasive or “weedy” is because the species is introduced to a new region (usually disturbed with access to water) that has suitable abiotic factors and little biotic competition or perdition.
C. hirsuta is known for its ability to shoot its seeds several meters in all sides when triggered by a passing animal. As something brushes up against the silique (long pods with dehiscent seeds) the weak epidermis separates and the coiled skin and seeds shoot out. This resulted in weaker C. hirsuta species to not proliferate past a few generations. In the case of C. hirsuta the annual reproduces prolifically during the fall and then dies. The seeds lie dormant through winter. The dead undergrowth creates a suitable environment for the seeds dispersed to sprout.
Looking at the mechanisms of seed separation is described as being the product of endocarp structure. The endocarp of the silique irregular thickness in the cell layers and mucilaginous pectin stores resulted in contractions in the silique whereby the endocarp would bend and break at the dehiscence zone. This is what gives the seeds shot off the coiled structure (Vaughn, Bowling, and Ruel 2011).
In Arabidopsis thaliana, a common study plant in botany, the endocarp was symmetrical. The seed dispersal is also not through explosive mechanisms. Not only is the cell wall thickness important, but the shape is also influential in the distribution of the seed. The square-shaped cells are associated with Cardamine sp. This shape is important to the dehiscent ability of the valve in the silique because of the pressure distribution throughout. With square walls, the thickness is more predictable to dehiscence (Hugo Hofhuis Angela Hay, 2017).
The plant’s own mechanism spreads the seeds, although animals and heavy wind may help the process start (Clark, 2012). This mechanism is seen in other plants too but is common in the Cardamine sp. when comparing the species in the Brassicaceae family.
“Cardamine Hirsuta L.,” Flora of Israel Online, accessed November 9, 2019, https://flora.org.il:443/en/plants/carhir/.
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“Plants Profile for Cardamine Hirsuta (Hairy Bittercress),” accessed November 9, 2019, https://www.plants.usda.gov/core/profile?symbol=CAHI3.
Kevin C. Vaughn, Andrew J. Bowling, and Katia J. Ruel, “The Mechanism for Explosive Seed
Dispersal in Cardamine Hirsuta (Brassicaceae),” American Journal of Botany 98, no. 8 (August 2011): 1276–85, https://doi.org/10.3732/ajb.1000374.
“Explosive Seed Dispersal.,” The New Phytologist 216, no. 2 (2017): 339–42, https://doi.org/10.1111/nph.14541.