Yellow starthistle

Composites -have been reported (8) to contain a wide variety of sesquiterpene lactones and lactones of this type have been previously found in both Russian knapweed and yellow starthistle (9,10,11,12). The wide range of biological activity associated with sesquiterpene lactones, e.g., cytotoxicity, phytotoxicity, antineoplasticity, etc. (8) suggested the possibility that these compounds may play a role in the allelopathy of both Russian knapweed and yellow starthistle. 

In addition to the sesquiterpene lactones, two chromenes, Eupa-toriochromene (I) and Encecalin (II) (14) have been isolated from yellow starthistle and have been shown to have some effects on germination and growth of lettuce. 

Plant Material. Russian knapweed and yellow starthistle were collec-ted in June along Highway 4, Contra Costa County, CA, between Brentwood and Stockton. The aerial parts of the plants were air dried, ground in a hammerraill with a 1/8" screen and extracted sequentially with Skellysolve-F and ether. 

Isolation of Chromenes. The Skellysolve-F extract of yellow starthistle was partitioned between Skellysolve-F/benzene/methanol/water (1 1 4 1). The lower layer was repeatedly chromatographed on silica-gel (column and preparative TLC) with Skellysolve-F/ether to give pure chromenes identified by comparison of physical properties with those reported (14) and by synthesis. 

The biological evaluation of the compounds isolated from Russian knapweed and yellow starthistle has led to some interesting features. 

Encecalin (I) causes a dwarfing of lettuce shoots at concentrations from lOppm and up. On the other hand, eupatoriochromene (II) causes very little dwarfing of the seedling but does inhibit germination of lettuce at lOOppm and above. The concentration of these two chro-raenes in yellow starthistle may indeed allow for some effect to be exerted on the surrounding plant community. 

Vidal, K., Guermache, F., and Widmer,T. (2004). In vitro culturing of yellow starthistle (Cen-taurea solstitialis) for screening biological control agents. Biol. Control 30, 330-335. 

Both eupatoriochromene and encecalin (9), from yellow starthistle (Centaurea solstitialis L., Asteraceae), retard seed germination and reduce radicle and hypocotyl growth of weed and crop plant seedlings (Merrill, 1989). 

Merrill, G. B., Eupatoriochromene and encecalin, plant growth regulators from yellow starthistle Centaurea solstitialis), J. Chem. Ecol., 15, 2073-2087 (1989). 

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