Yes, CLADISTICS is a Scrabble word!

Letter values in Scrabble US: C 3, L 1, A 1, D 2, I 1, S 1, T 1, I 1, C 3, S 1.

Is it a valid word?

CLADISTICS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a system of biological taxonomy based on the quantitative analysis of comparative data and used to reconstruct cladograms summarizing the (assumed) phylogenetic relations and evolutionary history of groups of organisms

Also: cladistic analysis.