This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 芠 is uncertain. It visually combines the grass radical 艹 with 文, but the original semantic or phonetic role of 文 in this character is unclear.
The top 艹 suggests a plant, and the bottom 文 can mean writing or pattern. Imagine a patterned leaf or a plant used to make paper for writing, but remember the actual meaning is uncertain.
For ブン, picture a patterned leaf being used as a bookmark in a book (ブン comes from 文's reading): the leaf marks the page, and ブン is the sound of the book closing.