Complex sentence: Simultaneous with the release of the 1998 APG classification was the publication of Kubitzki's major monograph on the monocotyledons and the Second Monocot Conference, which devoted an entire section to "Systematics of the Lilioids".
Split into simpler sentences: Simultaneous with the release of the 1998 APG classification were two events, the publication of Kubitzki's major monograph on the monocotyledons and the Second Monocot Conference. The Monocot Conference devoted an entire section to "Systematics of the Lilioids".