adiantum tenerum

NOUN
16 LETTERS · STARTS WITH A

adiantum tenerum is a valid 16-letter word worth 20 points in Scrabble and 26 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
A1D2I1A1N1T1U1M3T1E1N1E1R1U1M3
1 + 2 + 1 + 1 + 1 + 1 + 1 + 3 + 0 + 1 + 1 + 1 + 1 + 1 + 1 + 3 =20 PTS
DOUBLE WORD → 40TRIPLE WORD → 60
MEANING

What does adiantum tenerum mean?