Faculty of Philosophy: The Amoral Sciences Club has a page about great beards of philosophy. Somebody better make a page for the great beards of science. Here are some initial suggestions.
The philosopher page claims Charles Darwin, but honestly he was more of a biologist than a philosopher.
Dmitri Mendeleev has always in my mind been the top contender for the real beard of science. Russian, flowing, elemental.
Ivan pavlov had a neatly conditioned beard.
Louis Pasteur had a similar neat little beard. Not much space there for any microbiology.
Wilhelm Röntgen on the other hand had a very opaque beard.
Ludwig Boltzmann had a wilder beard that could only be described statistically.
August Erlenmeyer of course had a conical beard.
Antoine Becquerel had a radiant beard.
James Clerk Maxwell on the other hand had a more wavy beard.
ibn al-Haytham (Alhazen), al-Khwarizimi and the other islamic golden age scientists (plus all the greek scientists) likely had impressive beards, but exact records do not seem to have survived.
Conversely, if Aubrey de Grey gets SENS to work we will see his beard for a long time.