Rocket

Not only do rocket leaves taste great and are a great addition to almost any salad, they also make lovely little flowers in the process.
But to the (very) casual observer, such as moi, these flowers seem to be a little unusual in their overall structure. 
Most symmetrical flowers seem to have an odd number of petals positioned around the central stem, traditionally exemplified by the three-leaf clover - which continues to valiantly defy those seeking a four-leaf sample. 
But these guys come with an even number: four petals spaced at precisely 90 degrees apiece, forming a right-angled cross shape, with a small polleny bit in the middle.
The rounded ends of the petals are straight out of the normal flower petal playbook - don't seem to be a lot of straight-line petals out there - but the sharp-edged square cross shape is definitely not.
No idea why Nature prefers curves to straight lines, but s/he definitely does. Off the top of my head, can't think of a single plant or flower where a straight line continues on and stays a straight line, rather than inevitably  - slowly or more quickly - starting to turn all curvilinear.
Not particularly worried about it, mind you - curved lines, it's fair to say,  tend to look a whole lot better than straight, and are probably necessary to allow petals, for example, to be folded up within a bud casing with maximum space-saving efficiency. Can't imagine purely straight-line petals - square, rectangle or rhombus anyone? - being packed efficiently into the bud via several origami folds.
So still no clear idea why rocket flowers should have 4 petals when all around, other flowers have an odd number. Suspecting it doesn't - in the big scheme of things - really matter all that much; but find I'm not at all comfortable with unexplained anomalies like this, no matter how minor.
Best way around it is right through the middle, which is why I don't let the rocket get anywhere near to flowering stage before picking it or pruning it.