Marjoribanks was a pioneer in the field of Herbology. He collected and classified many rare and magical plants. Marjoribanks is credited with discovering Gillyweed, although Elladora Ketteridge had discovered it about a century earlier (FW).
"Marjoram" = a species of herb used in cooking. The name is also that of a Scottish Clan and pronounced "Marchbanks."
There is an ancient Scottish Clan called Majoribanks that first appeared in the 14th century, and one of their inherited names and titles was "Sir Dudley Majoribanks, the Baron of Tweedmouth." Perhaps the implication is that Beaumont was part of that distinguished family.
Scottish writer Margaret Oliphant wrote a novel satirizing the Victorian era called Miss Marjoribanks.