Complex sentence: Cronquist had placed most flowering petaloid monocots with six stamens in this very broad (and clearly polyphyletic) family, including the Amarylloidaceae which which includes species with an inferior ovary, which others separated into a distinct family, which created other problems.
Split into simpler sentences: Cronquist had placed most flowering petaloid monocots with six stamens in this very broad (and clearly polyphyletic) family. This included the Amarylloidaceae some species of which had an inferior ovary, and which others separated into a distinct family, although this then created other problems.