Besides Laminaria digitata 'kelp, tangle, cairn-tangle' which may be related to tangleweed (of Norse origin), the OED1 lists two other plants known as tangles: i.e., blue tangle (Gaylussacia frondosa, aka blue huckleberry, dangleberry, cited from Dunglison's Medical Lexicon), red tangle (Cuscuta epithymum, aka clover dodder, cited from Britten and Holland's English Plant-names).

The pertinent definition of tangle in the OED1 is "Applied to plants having long, winding, and often tangled stalks, as the species of Myriophyllum (Water Milfoil) and Potamogeton (Pondweed)". To tangle also means to snare or entrap.

Ceci n'est pas un seing.