The application of leaf phenolic evidence for systematic studies within the genus Pelargonium (Geraniaceae)

Abstract

In a leaf phenolic survey of 58 Pelargonium taxa, quercetin was almost universally present. Tannins were major components, namely proanthocyanidins and ellagitannins (in 53% of taxa) and free ellagic acid (in 50%). Myricetin (in 38%), flavone C -glycosides (in 36%) and luteolin (in 49% of taxa) were other regular constituents. A correlation was found between the presence of myricetin and proanthocyanidins. Although no individual compound or group of compounds appears to be a useful taxonomic marker for sectional classification, the data do indicate which sections are homogeneous, e.g. Otidia and Jenkinsonia . The chemistry supports the removal of some taxa from section Ligularia to the new sections Chorisma and Subsucculentia but does not distinguish between the latter two groups and indicates that section Ligularia is still an unnatural assemblage. Similarly, the data support the separation of P. reniforme and related species from section Cortusina into the new section Reniformia but P. odoratissimum appears misplaced in the latter group. The data suggest the placement of P. rodneyanum in section Peristera with the other Australian species. From a phylogenetic point of view the presence of ellagitannins or absence of tannins may be considered a more advanced state than the presence of proanthocyanidins and myricetin in the genus Pelargonium . For example, the most primitive state was found in P. crispum (section Pelargonium ) and the most advanced in P. multibracteatum (section Ciconium ). The chemistry also lends support for the division of the genus into two cytological groups based on chromosome size, in that most ellagitannin-producing species have large chromosomes while most proanthocyanidin-producing species have small chromosomes. There is agreement with the cytological and molecular data in grouping P. exstipulatum with P. album, P. reniforme and P. sidoides .