It is neither an American nor a British thing, but international plant morphology.
I apologize for citing Wikipedia, but it's quick and efficient:
disc/disk flowers/florets are characteristic of the sunflower family, Asteraceae, die Korbblütler, one of the largest plant families in the world, on every continent, even Antarctica.http://en.wikipedia.org/wiki/Asteraceae
The florets have five petals fused at the base to form a corolla tube and they may be either actinomorphic or zygomorphic. Disc florets
are usually actinomorphic, with five petal lips on the rim of the corolla tube. The petal lips may be either very short, or long, in which case they form deeply lobed petals. The latter is the only kind of floret in the Carduoideae, while the first kind is more widespread. Ray florets
are always highly zygomorphic and are characterised by the presence of a ligule, a strap-shaped structure on the edge of the corolla tube consisting of fused petals. In the Asteroideae and other minor subfamilies these are usually borne only on florets at the circumference of the capitulum and have a 3+2 scheme – above the fused corolla tube, three very long fused petals form the ligule, with the other two petals being inconspicuously small.http://de.wikipedia.org/wiki/Korbbl%C3%BCtler
Es gibt zwei grundsätzliche Blütenformen in der Familie: radiärsymmetrische Röhrenblüten (Scheibenblüten
) und zygomorphe Zungenblüten (Strahlenblüten
). Je nach Unterfamilie sind beide Blütenformen zusammen oder nur eine davon vorhanden.
I support the proposal, but drop [Amer.] Also, consider disc vs. disk.