Activity-directed fractionation of a CH(2)Cl(2)-MeOH (1:1) extract of Hofmeisteria schaffneri led to the isolation of a new phytotoxin characterized as 2'-(2' '-hydroxy-4' '-methylphenyl)-2'-oxoethyl acetate and designated the trivial name of hofmeisterin (1). In addition, the known compounds beta-carotene, euparin, and 3',4',4a',9a'-tetrahydro-6,7'-dimethylspiro[benzofuran-3(2H),2'-pyrano[2,3-b]benzofuran]-2,4a'-diol (2) were obtained. The identification of the isolates was accomplished by spectroscopic methods. The structure of 1 was unequivocally confirmed by synthesis. The methyl derivative 1a was also synthesized following the same strategy. Compounds 1 and 2 inhibited radicle growth of Amaranthus hypochondriacus (IC(50) = 3.2 x 10(-4) and 1.2 x 10(-5) M, respectively) and significantly inhibited activation of the calmodulin (CaM)-dependent enzyme cAMP phosphodiesterase (PDE) with IC(50) values of 4.4 and 4.22 microM, respectively.