( ( A weed ) ( ( is ( ( a plant ) ( growing ( where ( it ( ( 's not ) wanted ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN weed)) (VP (VBZ is) (NP (NP (DT a) (NN plant)) (VP (VBG growing) (SBAR (WHADVP (WRB where)) (S (NP (PRP it)) (VP (VBZ 's) (RB not) (VP (VBD wanted)))))))) (. .)))
A weed is a plant growing where it's not  wanted.
(ROOT (S (NP (NNS Weeds)) (VP (VBP are) (NP (NP (NNS plants)) (SBAR (WHNP (WDT that)) (S (VP (VP (VBP grow) (SBAR (WHADVP (WRB where)) (S (NP (NNS people)) (VP (VBP do) (RB n't) (VP (VB want) (NP (PRP them)) (PP (TO to))))))) (CC and) (VP (MD can) (VP (VB take) (PRT (RP up)) (NP (NP (NN space) (CC and) (NN use) (NNS resources)) (SBAR (WHNP (WDT which)) (S (VP (VBZ hinders) (NP (NP (NN growth)) (PP (IN of) (NP (ADJP (RBR more) (JJ desirable)) (NNS plants))))))))))))))) (. .)))