Phytomelanin and Systematics of the Heliantheae Alliance (Compositae)
Pandey, Arun K.; Stuessy, Tod F.; Mathur, Roshni R.
Plant Diversity and Evolution Volume 131 No. 3 (2014), p. 145 - 165
published: Apr 1, 2014
Phytomelanin is a hard, brown to black, resistant layer found in the pericarp of cypselae of taxa mostly restricted to eight tribes within the Heliantheae alliance of Compositae (also known as the Phytomelanin Cypsela Clade). Sixty-five species in 8 tribes (34 subtribes) were examined for surface sculpturing of the phytomelanin layer and its systematic import. The features examined were presence/absence of striations (longitudinal interruptions in the phytomelanin layer), and the occurrence and detailed characteristics of spines, pegs, and pores. Striations are seen in some Heliantheae s.s. but they are lacking in others; they are completely absent in Eupatorieae. A majority of taxa in the Heliantheae alliance have spiny phytomelanin surfaces except for Bebbia, Silphium, Ambrosia, and Clibadium, in which the phytomelanin is smooth or irregular. Fitchia possesses only calcium oxalate crystals. Most Eupatorieae are characterized by peg-like projections. Because phytomelanin is absent from most other tribes of Compositae, and since the Heliantheae alliance has been shown from molecular phylogenetic analyses to be highly derived, the occurrence of phytomelanin must be regarded as apomorphic within the family. The principal roles of phytomelanin probably involve adaptations for resistance against desiccation and/or defense against predators.