Systematics and character evolution of Tabernaemontaneae (Apocynaceae, Rauvolfioideae) based on molecular and morphological evidence

摘要

Tabernaemontaneae (Rauvolfioideae, Apocynaceae) are small trees with mainly animal-dispersed fleshy fruits and arillate seeds represented in the tropics of Africa, Asia, the Pacific and America. The tribe is characterized by complex indole alkaloids, thus its species play a prominent role in traditional medicine. Taxonomically, the Tabernaemontaneae have a convoluted history fraught with contention as to tribal, subtribal, generic and sectional delimitation, with some authors recognizing Ambelanieae and Macoubeeae as separate tribes and others including them in an expanded Tabernaemontaneae s.l. In the species-rich pantropical genus Tabernaemontana, seven sections and up to 30 segregate genera have been described during the past 100 years, giving it the dubious distinction of being the most disputed genus in Apocynaceae s.str. Here 420 new chloroplast DNA sequences from 104 species, including representatives of all satellite genera ever recognized in the Tabernaemontaneae, were analyzed phylogenetically to evaluate previous circumscriptions of Tabernaemontaneae and test the sectional treatment of Tabernaemontana. The Tabernaemontaneae s.l. as currently circumscribed was shown to be monophyletic. Of the 19 genera recognized in the most recent classification, 15 are maintained. The genera Bonafousia, Stemmadenia, Stenosolen and Woytokowskia are nested within Tabernaemontana. Of the seven current sections of Tabernaemontana, the four that included taxa from more than one continent were found to be para- or polyphyletic. All natural groups recovered within Tabernaemontana were found to correspond to geographic areas. Mapping of 29 selected morphological characters onto the molecular tree recovered recurrent suites of co-occurring character states and identified three synapomorphies characterizing the Tabernaemontaneae s.l.: (1) specialized anthers with massive lignified guide-rails; and a differentiated style-head with (2) a five-lobed upper crest and (3) a thickened basal flange. A new combination for the subtribe Ambelaniinae and the necessary new combinations resulting from merging Stemmadenia into Tabernaemontana are made.