This is a question that came to me yesterday when I started looking into brackish, while hoping to expand my knowledge.
There are indeed brackish plants, no where near as many as freshwater though.
I’d be interested to see the replies to this.
I can't remember off the top of my head, but yes, there are several brackish plants. Java Fern and Java moss are some, and I think anacharis. If you have the space, mangroves!