Seed coat is not thin, membranous in:
Gram
Maize
Coconut
Groundnut
The seed coat forms from the integuments that surround the ovule. Coconut is thick and rigid, which shields the embryo from mechanical harm and drying out. Consequently, the seed coat of coconut seed is thick, but the seed coats of groundnut, gram, and maize seeds are thin and membranous.