Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


As part of a chemical-ecological study of the Florida scrub community, Ceratiola ericoides (Empetraceae) and Calamintha ashei (Lamiaceae) were chemically investigated for natural products with possible allelochemical activities. The chromatographic separations and chemical investigations were guided by germination and radicle growth bioassays performed on seeds of commercial lettuce (Lactuca sativa) and Schizachyrium scoparium, a native grass of the Florida sandhill community. From the dichloromethane extract of aerial parts of C. ericoides, 2', 4'-dihydroxychalcone, the dihydrochalcones angoletin and 2',6'-dihydroxy-4-methoxy-3',5'-dimethyldihydrochalcone, the flavanones 8-methylpinocembrin, 6,8-dimethylpinocembrin and 7-hydroxyflavanone were isolated along with the triterpenes erytrodiol and ursolic acid. Significant inhibition on S. scoparium radicle growth was observed with 6,8-dimethylpinocembrin when applied in a saturated aqueous solution of ursolic acid. From the active region of the ethyl acetate extract of C. ericoides, catechin, epicatechin, (A-2) dimer and related proanthocyanidins were isolated. Although mixtures of proanthocyanidins showed activity, A-2 alone exhibited no inhibitory effects on test seeds. Surface washings of fresh C. ericoides leaves provided the novel dihydrochalcone ceratiolin. Ceratiolin decomposes spontaneously to form, besides other unidentified products, hydrocinnamic acid. Pure ceratiolin does not inhibit germination and radicle growth. However, hydrocinnamic acid shows significant inhibitory activity on both, L. sativa and S. scoparium. From active chromatographic fractions of the dichloromethane extract of Calamintha ashei, two menthofurans, the known evodone and the new monoterpene calaminthone as well as the sesquiterpene caryophyllene oxide were isolated. The above terpene mixture completely inhibited S. scoparium germination but bioassays performed with pure compounds exhibited no significant allelopathic activity. Volatility test of evodone showed strong inhibition on germination of S. scoparium seeds. A dramatic increase in inhibition of the radicle length of S. scoparium by evodone dissolved in a saturated aqueous solution of ursolic acid was observed when compared to a pure aqueous solution of evodone. Tests for possible micelle formation, using the acridine fluorescence method with natural products and the surfactants ursolic acid and emulphogen indicated that mixtures of natural products in leaf leachates lead to micellar solutions which may aid the dissolution and therefore effectiveness of nonpolar allelochemicals.