"Imperfect fungi" are "imperfect" not because they lack something but because science understands their life cycles "imperfectly." In technical texts this group is often referred to as the Deuteromycota or Deuteromyctes. The group contains a hodgepodge of fungi, the members of which will eventually be determined to be club, sac or conjunction fungi (or maybe something entirely new), and no longer be considered "imperfect."

If you think about it, it's kind of neat to run into a corner of science where scientists are even at this moment just throwing up their hands and saying "We don't know how these fungi reproduce!" It's even neater when you realize that many "imperfect fungi" are very common.

For example, around my trailer in southwestern Mississippi the most common tree is the Sweetgum. It happens that nearly every leaf on every Sweetgum tree here is infected by the "leafspot fungus" shown at the right -- and every year the same leaf disease strikes. The fungal disease,  probably Gloeosporium nervisequum, is a kind of  filamentous fungus and it's an "imperfect" one. As summer progresses the reddish spots enlarge and eventually turn black, making the leaf look not nearly as pretty as it does in this picture. I can't tell you much more about the life cycle of this fungus because its life cycle is "imperfectly known"...