title: Phylogenetic position of Guihaiothamnus (Rubiaceae): its evolutionary and ecological implications.
abstract: Guihaiothamnus (Rubiaceae) is an enigmatic, monotypic genus endemic to southwestern China. Its generic status has never been doubted because it is morphologically unique by having rosette habit, showy, long-corolla-tubed flowers, and multi-seeded indehiscent berry-like fruits. The genus has been postulated to be a relict in the broad-leaved forests of China, and to be related to the genus Wendlandia, which was placed in the subfamily Cinchonoideae and recently classified in the tribe Augusteae of the subfamily Dialypetalanthoideae. Using combined evidence from palynology, cytology, and DNA sequences of nuclear ITS and four plastid markers (rps16, trnT-F, ndhF, rbcL), we assessed the phylogenetic position of Guihaiothamnus in Rubiaceae. Our molecular phylogenetic analyses placed the genus deeply nested within Wendlandia. This relationship is corroborated by evidence from palynology and cytology. Using a relaxed molecular clock method based on five fossil records, we dated the stem age of Wendlandia to be 17.46 my and, the split between G. acaulis and related Wendlandia species in southwestern China to be 2.11mya. This young age, coupled with the derived position in Wendlandia, suggests an evolutionary derivation rather than an evolutionary relict of G. acaulis. Its rosette habit and large showy flowers, which are very distinctive from other Wendlandias, are interpreted as a result of recent rapid adaptation to rock and cliff habitats.
authors.affiliation: Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China; Dongguan Institute of Agricultural Science, Dongguan, China.
authors.forename: Peiwu
authors.initials: P
authors.lastname: Xie
authors.affiliation: Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
authors.forename: Tieyao
authors.initials: T
authors.lastname: Tu
authors.affiliation: Bergius Foundation, The Royal Swedish Academy of Sciences and Botany Department, Stockholm University, Stockholm, Sweden.
authors.forename: Sylvain G
authors.initials: SG
authors.lastname: Razafimandimbison
authors.affiliation: Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
authors.forename: Chengjie
authors.initials: C
authors.lastname: Zhu
authors.affiliation: Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China. Electronic address: dx-zhang@scbg.ac.cn.
authors.forename: Dianxiang
authors.initials: D
authors.lastname: Zhang
mesh_terms: D005075:Biological Evolution; D002681:China; D055669:Ecological and Environmental Phenomena; D005580:Fossils; D010802:Phylogeny; D054817:Pollination; D019666:Rubiaceae / Q000033:anatomy & histology / Q000145:classification* / Q000235:genetics; D017422:Sequence Analysis, DNA
keywords: Adaptation; Augusteae; Dialypetalanthoideae; Monotypic genus; Wendlandia