There are a number of different varieties of the radish plant. Some examples can be found in the links below:

Radishes:
http://www.funet.fi/pub/sci/bio/life/plants/magnoliophyta/ma...

black radish (musta retikka):
http://www.isoaidinkasvit.fi/kasvit/13/1324vretikka.htm
http://www.madawas.com/herbtour/blackradish.htm

white radish/mooli (valkoinen retikka):
http://www.finfood.fi/finfood/kasvikset.nsf/0/D2F6A54AD35C15...
http://www.agric.nsw.gov.au/Hort/Fmrs/Asian_veg/wradish.htm
Radishes:
http://www.dooyoo.co.uk/review/370228.html
http://www.xrefer.com/entry/409877

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Note added at 2002-08-12 08:32:48 (GMT)
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Raphanus Savitus Group of vegetables