Autotoxic species are those which adversely affect their own seeds' germination and/or seedling development. Cistus ladanifer L (labdanum or jara) has been shown to have a pattern of allelopathic behaviour against the herbs that share its habitat. The present work studied whether an autotoxic effect also exists. The aqueous solution obtained from washing jara leaves was found by itself to inhibit germination and cotyledon emergence of the species' seeds. When these same trials were carried out in soils, autotoxicity was observed only from leaves and soils collected in winter. This was so both in soils collected away from the influence of the jaral to which was added the greatest concentration of aqueous extract prepared from the leaves, and in soils collected within the jaral, except that in the latter group of soils germination was inhibited with or without the addition of C. ladanifer extracts. This autotoxic behaviour could be involved in the species' own population control, and would explain the scant self-regeneration within established C. ladanifer stands.

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The exudate of Cistus ladanifer L. consists mainly of two families of secondary metabolites: flavonoids and diterpenes. The amount of flavonoids present in the leaves has a marked seasonal variation, being maximum in summer and minimum in winter. In the present study, we demonstrate that the amount of diterpenes varies seasonally, but with a different pattern: maximum concentration in winter and minimum in spring-summer. The experiments under controlled conditions have shown that temperature influences diterpene production, and in particular, low temperatures. Given this pattern, the functions that these compounds perform in C. ladanifer are probably different.

A lower herb richness and diversity in the presence of Cistus ladanifer is attributed to the allelochemicals exudate from its leaves and stem. The objective of the present study was to determine allelopathic activities of C. ladanifer exudates and the persistence of potential allelochemicals in soil environment. The results showed that the aglycone flavonoids degrade very slowly in the soil, remaining a very long time with no further external input. Although the amounts of aglycone flavonoids in soils are low (of the order of μg/g soil), their high persistence may facilitate inhibition of the germination and growth of other species or an indirect effect by altering the soil's characteristics, providing a possible explanation for the phytotoxic activity attributed to C. ladanifer.

Cistus ladanifer exudate is a potent inhibitor of the sarcoplasmic reticulum Ca2+-ATPase (Ca2+-pump) of rabbit skeletal muscle, a well-established model for active transport that plays a leading role in skeletal muscle relaxation. The low concentration of exudate needed to produce 50% of the maximum inhibition of the sarcoplasmic reticulum Ca2+-ATPase activity, 40-60 microg/ml, suggests that eating only a few milligrams of C. ladanifer leaves can impair the relaxation of the mouth skeletal muscle of herbivores, as the exudate reaches up to 140 mg/g of dry leaves in summer season. The flavonoid fraction of the exudate accounts fully for the functional impairment of the sarcoplasmic reticulum produced by the exudate (up to a dose of 250-300 microg/ml). The flavonoids present in this exudate impair the skeletal muscle sarcoplasmic reticulum function at two different levels: (i) by inhibition of the Ca2+-ATPase activity, and (ii) by decreasing the steady state ATP-dependent Ca2+-accumulation. Among the exudate flavonoids, apigenin and 3,7-di-O-methyl kaempferol are the most potent inhibitors of the skeletal muscle sarcoplasmic reticulum. We conclude that the flavonoids of this exudate can elicit an avoidance reaction of the herbivores eating C. ladanifer leaves through impairment of mouth skeletal muscle relaxation.