"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, where I used to live in southwestern Mississippi the most common tree was the Sweetgum. It happens that nearly every leaf on every Sweetgum tree around my home was infected by the "leafspot fungus" shown at the right -- and every year the same leaf disease struck. The fungal disease, probably Gloeosporium nervisequum, is a kind of filamentous fungus and it's an "imperfect" one. As summer progressed the reddish spots enlarged and eventually turned 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"...