Large Scale Geographical Mapping of Essential Oil Volatiles in Heracleum (Apiaceae): Identification of Novel Compounds and Unraveling Cryptic Variation

Abstract

Conspecific populations of plants in their native range are expected to show considerable variation due to long-term ecological and evolutionary factors. We investigated the levels of secondary metabolites in Heracleum including H. persicum a valuable medicinal plant to depict the magnitude of cryptic variation and the potential significance of novel chemical traits. The essential oil volatiles from fruits of 34 populations from different species of Heracleum in Iranian distribution range and a native of H. sphondylium and an invasive population of H. persicum from Norway were analyzed with GC/MS. Out of 48 compounds identified, a contrasting pattern in the level of two major compounds, octyl acetate and hexyl butyrate was found among all studied species. Interestingly, a significant geographic pattern was observed; the hexyl butyrate/octyl acetate ratio was high (range 1.8 - 3.2) in the northwestern Iranian populations of H. persicum compared to that in northern and central populations (range 0.3 - 0.9). Four populations from Zagros mountains also exhibited a unique composition. Anethole was found in two populations of H. persicum from central Zagros, which has not been previously reported for essential oil of fruits of Heracleum so far. The results suggest high efficiency of large scale sampling from distribution range of species in identifying novel compounds. The unique pattern of geographic structuring also provides novel information to unravel cryptic variation in Heracleum.

The taxonomic significance of ddRADseq based microsatellite markers in the closely related species of Heracleum (Apiaceae)

“…In Flora Iranica the presence of abaxial leaf trichome is listed as a diagnostic criteria in the latter species [14]. However, other molecular data from these species, including an ITS and trnL-trnF nucleotide analysis, together with a volatile oil composition study, also confirm our observed pattern which suggests a lack of differentiation amongst H. persicum and H. rechingeri populations [4,6,12], and perhaps that the abaxial leaf trichome is an unreliable trait in resolving H. rechingeri and H. persicum. Since inter-specific hybridization has been reported to be prevalent in Heracleum [2,3], the observed patterns can also be interpreted as a lack of fixed differentiation resulting from an introgression of alleles between the congeneric species.…”

“…In addition, the three populations from H. pastinacifolium are not genetically differentiated from populations of a morphologically similar species, H. anisactis and H. transcacasicum. Similar studies using ITS and rpl32-trnL nucleotide sequences, or from the analysis of the chemical constituents of essential oils derived from the fruits, have also delimited the thin-and thick stem species, even though H. pastinacifolium and H. anisactis remain similar [4,12]. Limited numbers of cross-amplified microsatellite markers in H. lasiopetalum reveal a distant relatedness of this species within Heracleum.…”

“…Heracleum is a taxonomically complex genus, and previous investigations have found incongruent results between observed molecular clusters, morphological data and taxonomic classifications [4][5][6]. Lack of appropriate species-specific genetic markers hinders progress to untangle clear relationships within a species complex in a cost-effective way [2][3][4]6]. This is particularly challenging for a genus with species having important ecological roles, or which are rare, or alternatively invasive, or of special interest for conservation management.…”

“…In many plant species complexes, factors such as hybridizations, phenotypic plasticity and high variability across the geographical distribution range makes species identification based on morphological characters challenging [1][2][3]. Heracleum is a taxonomically complex genus, and previous investigations have found incongruent results between observed molecular clusters, morphological data and taxonomic classifications [4][5][6]. Lack of appropriate species-specific genetic markers hinders progress to untangle clear relationships within a species complex in a cost-effective way [2][3][4]6].…”

“…Molecular studies have shown that the seemingly cosmopolitan genus Heracleum (Apiaceae) is not monophyletic [5,11]. There is also extensive variation associated with genetic, chemical and morphological traits at various geographical levels within and among species [3][4][5]12]. The genus consists of more than 100 species found mainly in the West-Asian/Caucasus and Syno-Hymalian regions, the former region being suggested as a center of origin for the genus [3,11,13].…”