Floral evolution and pollinator diversification in Hedychium J.Koenig (Zingiberaceae): one of Mr. Darwin's tropical fantasies

Abstract

PREMISEHedychium J.Koenig (ginger lilies: Zingiberaceae) is endemic to the Indo-Malayan Realm (IMR) and is known for its fragrant flowers. Two different pollination syndromes characterize the genus: diurnal or bird pollination and nocturnal or moth pollination systems. To date, no attempt has been undertaken to understand the evolution of floral traits in this genus. METHODSWe estimated ancestral character-states, phylogenetic signals, and character correlations for thirteen discrete and eight continuous floral traits representing 75% species diversity of Hedychium. Diversification rate estimation analyses were also employed to understand trait-dependent diversification in the genus. RESULTSInflorescence structure, cincinnus capacity, and curvature of floral tubes revealed strong phylogenetic dependence, whereas number of open flowers per inflorescence per day, color of the labellum, and exertion of the stigma characterized higher ecological effects. Diversification rate estimations suggested that the labellum width, floral tube length, and labellum color played a major role in the evolutionary diversification of Hedychium. CONCLUSIONSWe identified bract type and cincinnus capacity as synapomorphies for Hedychium, while the island-specific clade III was characterized by slender cylindrical inflorescence, coiling of floral tubes, and longer bract to calyx ratio. The circum-Himalayan clade IV is the most speciose, derived, and with most variable floral traits. Although floral color and size lacked any association with pollinator-specific traits (moth and bird pollination), pale colored flowers were most common in the early diverging clades (clade I, II-el., and II-de.), indicating their ancestral nature, when compared to brightly colored flowers.