Yes, COCKLEBURS is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, C 3, K 5, L 1, E 1, B 3, U 1, R 1, S 1.

Is it a valid word?

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

any coarse weed of the genus Xanthium having spiny burrs
burdock having heart-shaped leaves found in open woodland, hedgerows and rough grassland of Europe (except extreme N) and Asia Minor; sometimes cultivated for medicinal and culinary use

Also: cockle-bur, cockle-burr, great burdock, greater burdock, arctium lappa.

Not playable in Scrabble US: COCKLEBURR.