8,9 A: Fungus that will keep your clothes closed (6,8): ??M?O? MUSHROOM
15A: Geometric shape that has no horse upon it (7): POLYGON ?
1D: Less important worker of lower rank (11): A???R?????E
2D: Silent bird , to judge by its name (4,4): DUMB S???
4D: Large plant for steering Cockney ships (3, 4) : ELM TREE?
Thanks in advance