Fern moss may refer to several varieties of moss that produce feathery fronds and can form a moss carpet across grass or bare patches of ground:

Hylocomium splendens

• Fissidens bryoides – lesser fern moss
• Hylocomium splendens or Hylocomium proliferum – mountain fern moss
• Thuidium species including:
  • Thuidium abietinum – wiry fern moss
  • Thuidium delicatulum – common fern moss
  • Thuidium recognitum – hook-leaf fern moss

Possibly also:

• Drepanocladus species including:
  • Drepanocladus fluitans
  • Drepanocladus uncinatus