Shamrock ist nur der vierblättrige Klee, clover jeder andere.

mann kann auch "four leave clover - 4 blättriges kleeblatt"

denke ich

Being English myself, I'm not sure of the difference, but Google.co.uk found me an explanation from the BBC

http://news.bbc.co.uk/1/hi/uk/3519116.stm

Man kann was? Sagen? OK. Schreiben sollte man aber "4-blättriges Kleeblatt".

http://ask.yahoo.com/20040317.html
What's the difference between clover and shamrock?
Poppy Fields
Greenleaf, Wisconsin
Dear Poppy:
A shamrock is a common name for a clover. But as American botanist Kathleen Pelkki explains, a shamrock is a common name for any number of plants belonging to the genus Trifolium, from the Latin meaning "having three leaves."

The plant most commonly referred to as shamrock is white clover or Trifolium repens. The Irish word "seamrog," from which shamrock comes, means "little clover." Black medic, wood sorrel, and the hop clover have also been called shamrocks.

There is some debate over this issue. We found an Irish FAQ that claims that shamrocks are smaller than clovers, though they are both species of Trifolium. We couldn't verify this with other online resources.

For a thoroughly detailed investigation of this issue, we refer you to Jane Lyons' article "The Real Shamrock." She states unequivocally that a true Irish Shamrock is a white clover or Trifolium repens. As evidence, she refers to Irish naturalist Nathaniel Colgan's 1893 manifesto, "The Shamrock: A Further Attempt to Fix Its Species."

Shamrocks came to be associated with St. Patrick's Day because the patron saint of Ireland used the three-leafed plant as a metaphor for the Christian concept of Father, Son, and Holy Ghost.

The debate seems long not being over.

wenn Hochdeutsch, dann schon "vierblättriges"
glaubt mir, bin Germanistin mit Diplom!

Die Pflanze heißt clover und hat normalerweise drei Blätter. Ein shamrock ist ein vierblättiger Klee und gilt als irisches Nationalsymbol. Da der vierblättiger Klee auch als allgemeines Symbol des güten Glücks gilt, wird er auch ein "(lucky) four-leaf clover" genannt.

But don't use vierblättrig to describe the shamrock - it's usually got three leaves, like the clovers.

Well, I always thought that only a four-leaf clover was a shamrock. It seems I was wrong about that. AFAIK, however, the word “shamrock” is only used in the context of describing the Irish symbol in the UK.

But don't use vierblättrig to describe the shamrock - it's usually got three leaves, like the clovers. Only the rare, "lucky" version has four leaves. As far as I know, a normally three-leaved clover/shamrock occasionally produces a four-leaved shoot.

You can keep children busy for ages looking for a four-leaved clover in a clover patch - they're most unlikely to find one.

Das Shamrock ist definitiv dreiblättrig, da St Patrick den Iren die Dreifaltigkeit erklärt haben soll.

Es ist enfach nur eine andere Art, so wie es Klee gibt, aber eben auch Weißklee, Rotklee, etc.

Apologies to Steve - I wasn't deliberately trying to contradict you, we were just posting at the same time.

No problem, Villager, everything you said was right. I was just busily correcting my own long-held misconceptions about shamrocks having four leaves.

Eigentlich dürfte man ja nicht "vierblättriger Klee" sagen, denn das wäre eine Kleepflanze, die vier Blätter hat. In wirklichkeit hat das Kleeblatt selbst vier Unterteilungen.