Antherostele Bremek. is an understudied genus of Rubiaceae endemic to the Philippines formerly comprising four species of shrubs or small trees distributed in Luzon and Visayas. In this first molecular study of the genus, the ITS (nrDNA) was utilized to determine the monophyly of Antherostele, reconstruct its phylogeny, and resolve its placement in Rubiaceae. Furthermore, an update on the assessment of its conservation status of the included species in the genus was done. Antherostele is monophyletic and is nested within the tribe Urophylleae of subfamily Rubioideae which confirms its segregation from Urophyllum and its placement within Urophylleae as proposed by earlier authors based on morphology. However, the relationships of Urophylleae members remain unresolved. Antherostele is united by reflexed corolla, hairs on upper side of the corolla lobes and syngenesious stamens. The montane A. luzoniensis with small leaves is found to be sister to the rest of Antherostele species. Antherostele is hypothesized to originate from montane regions and diversified by forming larger leaves following dispersal to the shaded forest understory. From the five species of Antherostele currently recognized in the study, two are endangered (A. banahaensis, A. grandistipula) and three are critically endangered including a new species (A. callophylla, A. luzoniensis, A. sp. nov.) following the criteria of IUCN.
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E. Robbrecht and J. Manen, “The Major Evolutionary Lineages of the Coffee Family (Rubiaceae, Angiosperms). Combined Analysis (nDNA and cpDNA) to Infer the Position of Coptosapelta and Luculia, and Supertree Construction Based on rbcL, rps16, trnL-trnF and atpB-rbcL Data. A New Classification in Two Subfamilies, Cinchonoideae and Rubioideae,” Systematics and Geography Plants, Vol. 76, 2006, pp. 85-146.
J. E. Smedmark, C. Rydin, S. G. Razafimandimbison, S. A. Khan, S. Liede-Schumann and B. Bremer, “A Phylogeny of Urophylleae (Rubiaceae) Based on rps16 Intron Data,” Taxon, Vol. 57, No. 1, 2008, pp. 24-32.
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