Only one I can think of is Allium 'Christophii' (not quite Christopher)which is a bulb,huge globes of metallic purple star shaped flowers 8inch across.
Sure some clever person on here will think of something else though :-)

There is a Clematis called Christopher have a look on
www.hull.ac.uk go to A-Z and look in letter C

‘The Royal Horticultural Society Horticultural Database’, available at www.rhs.org.uk has a search page which, if you enter Christopher shows:

http://apps.rhs.org.uk/rhsplantfinder/pfgenera.asp
(Copy and paste the line above into your address field and press Go)

You then just click on each of the resulting entries. Many have surnames too, but you can try them all.

A couple of results are:

Aconitum lycoctonum - one common name is "Christopher's herb".

Osmunda regalis (Osmunda regalis L.) - one common name is "herb Christopher".