The genus Amorphophallus Blume (Araceae): phylogenetic studies and evolutionary patterns

Abstract

The genus Amorphophallus (ca. 237 species) is one of the largest genera of the Araceae and morphologically very diverse. The high species number and the high morphological variation make the understanding of the evolutionary history of the genus challenging. Therefore, in Publ.1, a new molecular phylogenetic analysis using nuclear (ITS1) and plastid (rbcL and matK) sequences based on 157 species is conducted and the resulting phylogenetic tree is used to delimit four subgenera. Moreover, several morphological and biochemical characters, some of which are related to mimicry, are explored in the phylogenetic context, demonstrating the congruence between molecular and some morphological and biochemical traits. However, several species complexes are difficult to resolve. Subsequently, the species boundaries are explored in Publ. 2 through the creation of artificial hybrids. As for the traits related to mimicry, at least two types of mimicry are encountered in several Amorphophallus species. One is a unique type of defensive colouration, petiolar lichen mimicry, providing the fleshy petiole the look of an old woody stem. Lichen mimicry in Amorphophallus has been previously described; however, in a few species only. Therefore, in Publ. 3, defensive colouration is explored in 138 Amorphophallus species, with an emphasis on lichen-like patterns. Mimicry of specific lichen types is identified in 69% of the investigated Amorphophallus species and the results are discussed in the context of the phylogenetic analysis. Deceit flowers, more precisely oviposition-site mimicry, is the second type of mimicry. The inflorescences mimic substrates, usually decomposing organic matter, which are used by Coleoptera and Diptera for feeding or breeding. Amorphophallus species are assumed to have specialised plant-pollinator interactions, involving specific pollinators, which in turn have contributed to the species richness of the genus. However, the available information about Amorphophallus pollinators is scarce; moreover, several reports are anecdotal. Therefore, the observations on visitors and pollinators in Amorphophallus are compiled, reviewed and discussed and the specificity of the plant-pollinator interaction is explored in Publ. 4. The key element of oviposition-site mimicry are the scent compounds. In previous investigations, the scent compounds of 92 Amorphophallus species have been identified and categorised to explore the evolution of floral odours in Amorphophallus. However, only few distinct evolutionary trends could be identified. One possible cause that has not been previously discussed, is intraspecific odour polymorphism. Consequently, the emitted scent compounds in Amorphophallus and the subjective odour classifications are reviewed and screened for odour polymorphism in Publ. 5. Significant odour polymorphism is identifiable in some Amorphophallus species, underlining the necessity for more investigations assessing the intraspecific variation of emitted scent compounds. Publ. 6 addresses thermogenesis, a floral temperature increase assumed to enhance scent volatilization during anthesis. The floral temperature of 80 Amorphophallus species has been measured and the resulting temperature curves have been used to explore and discuss the impact of thermogenesis on the evolution of the genus. The temperature curves show an unprecedented variation within the genus; moreover, the functionality of thermogenesis remains contentious, calling for further investigations. Lastly, using 36 Amorphophallus species, a phylogenomic study is conducted in Publ. 7, investigating the interrelationship between the main clades and providing a timeline for the evolution of the genus. For the first time, a phylogenetic hypothesis is presented that resolves the interrelationship between the African and the Asian clades. In a final chapter, the morphological variation is discussed in regard to the molecular phylogeny and evolutionary constraints. Moreover, further aspects of defensive colouration, odour polymorphism, thermogenesis and the plant-pollinator interaction are discussed.