Morphological and chemical variations in natural populations of Pituranthos triradiatus in the Negev Desert

Abstract

Morphochemical variations among six populations of Pituranthos triradiatus have been studied in the Negev Desert, in areas located within an air distance of 80 km, with an aridity gradient from 150 to 50 mm of average annual rainfall. Based on morphological florisitic characters, as well as on the content of furanocoumarins in the shoots of the shrub, five different populations have been observed. Some of the morphological characters which are commonly used for classification in the species level were found useful for the subspecies level, e.g. number of rays per umbell or per umbellet. Others, such as the shape of petals or stylopodium, or petals color, were not efficient. In addition to the commonly used characters, average fruit weight was found useful. Seven different furanocoumarins were found in the examined populations of P. triradiatus. Four of them (isoimperatorin, imperatorin, bergapten and isopimpinellin) were in each of the populations studied. Three other furanocoumarins were found to be specific: cnidilin for the Revivim population; pimpinellin for Zin and isobergapten for the Marzeva and Neqarot populations. In addition to these specific furanocoumarins, the amount of bergapten in the shoots seems to be specific for each population and is suggested to be used as a chemical marker for further screening of chemotype differentiation in R. triradiatus. It is suggested that the differences in the floristic characters, as well as in the content of furanocoumarins are of genetic nature and not an artifact. To better establish this view and to evaluate the efficiency of furanocoumarins content as a chemotaxanomic marker, further work is needed. It is also suggested that levels of isolation among the investigated population account for the differences encountered. No association could be found between different levels of aridity and different levels of furanocoumarin content.