Recent studies have shown that the European plant Centaurea maculosa (spotted knapweed), an invasive species in North America, rhizosecretes a phytotoxin (±)-catechin (Bais et al., 2002, 2003), although the quantities of (±)-catechin produced and its potency as a phytotoxin under some conditions remains uncertain (Blair et al., 2005).
Source: wiktionary