 Later the plant forms a seed head that resembles that of the dandelions but is distinctly larger.The seeds themselves (known as achenes) are 2–4 cm long but featherweight, weighing about 8 mg each on average.There is some natural variation between the central and peripheral achenes in the seedhead, with the peripheral ones being generally darker and heavier, and having a higher concentration of phenolic compounds; this may enhance their survival potential.