Noble hops (Saaz, Spalt, Tettnang etc) have very subtle aromas because they are classy. Whereas less noble hops (Amarillo, Galena, Cascade) have strong aromas because they are tarts! Myrcene has a floral aroma and is found in high concentrations in the less-noble hops and is in part responsible for this tartiness. Personally I blame the parents.
Myrcene gets its name from the plant Myrcia which is especially rich in the substance.