Phenological and population variation in iridoid glycosides of Plantago lanceolata (Plantaginaceae)

Relatively little is known about the natural variation in the secondary plant chemistry, or the potential sources of this variation, in Plantage lanceolata (Plantaginaceae) (Narrow-leafed plantain). To assess this chemical variation, P. lanceolata plants were collected monthly from five field populations located in Boulder County, Colorado, over the course of one growing season (July through October). There were significant effects of both population and time of harvest on the biomass and the iridoid glycoside content of the leaves and reproductive stalks of P. lanceolata plants. Although environmental differences between sites were not specifically quantified, two sources of variation, mechanical damage and elevation, appeared to be important sources of variation among these populations. To test the hypothesis that plants that had higher iridoid glycoside concentrations were smaller, i.e. that there was a cost to chemical defense in P. lanceolata, we tested for a negative correlation between biomass and iridoid glycosides. We found no correlation between the biomass and the iridoid glycoside content of the above-ground tissues of P. lanceolata, providing no indication of a cost. (C) 1997 Elsevier Science Ltd.