Question

why some fungi are called as 'imperfect fungi'???

Answer 1

Because fungi is known as fungi so fungi is called as fungi

Answer 2

the imperfect fungi are kept in class deuteromycetes . they are called as imperfect because sexual reproduction is absent in these forms.
they reproduces only by asexual spores called conidia. they have separate and multinucleate mycelium.
e.g... alternaria, trichoderma , colletotrichum.