Artabotrys angustipetalus (Annonaceae), a new species from Thailand, including a plastid phylogeny and character evolutionary analyses of thorn occurrence in Artabotrys

Abstract

Artabotrys R. Br. is one of the larger genera of Annonaceae with over 100 species distributed throughout the palaeotropics plus northern Australia. Although the genus is morphologically very well circumscribed, species delimitation is quite problematic owing to overlapping morphological characteristics. In Thailand, 20 species of Artabotrys have been reported, including A. multiflorus C. E. C. Fisch. Detailed comparisons with the type specimen from Myanmar revealed that A. multiflorus occurring in Kanchanaburi Province of Thailand represents a new species herein described as A. angustipetalus Photikwan and Chaowasku. The new species differs from A. multiflorus by having fewer flowers per hook, linear (vs oblong to oblong-lanceolate) petals, acute (vs obtuse) petal apex, longer and narrower petals and fewer carpels per flower. A multi-locus plastid phylogeny including an accession of A. angustipetalus and 30 accessions of other species of Artabotrys has been reconstructed. The results uncover a well-supported clade consisting of thorn-bearing species of Artabotrys, with A. angustipetalus recovered outside this clade. To understand the evolution of thorns in Artabotrys, ancestral character-state reconstructions were carried out; this trait is inferred to have evolved only once in Artabotrys. The benefits of thorns in Artabotrys species are discussed and hypothesized.