Ferns are known for having large chromosome counts and huge genome size. I think RadSeq would have  a rather  low coverage.  Probably transcriptome data would give more bang for your bucks for these organisms.

Kew C value data for Poplypodiophyta

1C (pg)

C Mean 9.54

C Min. 0.77

C Max. 25.46

Standard deviation 4.

Kew C value data for OPHIOGLOSSACEAE

1C (pg)

C Mean  31.05

C Min.  2.60

C Max.  65.55

Standard deviation 28.04