Updated taxonomy, distribution and systematic position of the little-known genus Treutlera (Apocynaceae, Marsdenieae)

• Published in: Plant systematics and evolution 2023-08, Vol.309 (4), p.23, Article 23
• Main Authors: Liao, Miao, Wang, Hui, Ge, Bin-Jie, Wang, Zi, Zhong, Xin, Zhang, Cai-Fei, Hu, Guang-Wan
• Format: Article
• Language: English
• Subjects: Apocynaceae; Biomedical and Life Sciences; Lectotypes; Life Sciences; Marsdenia; Mentzelia oreophila; Morphology; Phylogenetics; Phylogeny; Plant Anatomy/Development; Plant Ecology; Plant Sciences; Plant Systematics/Taxonomy/Biogeography; Rare species; Taxonomy
• ISSN: 0378-2697; 1615-6110; 2199-6881
• DOI: 10.1007/s00606-023-01860-4

Treutlera is hitherto a monotypic genus of the tribe Marsdenieae in the family Apocynaceae, comprising the single rare-known species  T. insignis known from Bhutan, India, and Nepal. Recent phylogenetic studies have resulted in great changes in the generic classification of Marsdenieae, yet left the unsampled Treutlera on an unclear generic status. Here we report its new occurrences in southeastern Xizang, China and test the generic status for the first time by using molecular evidence. Phylogenetic analysis highly supported the position of Treutlera  embedded within the Marsdenia oreophila subclade which is separated from the Marsdenia s.s. subclade. Because of the internal relationships poorly resolved within the  M.  oreophila  subclade and less-known morphological variations, Treutlera as the earliest generic name available for this subclade should be recognized and is tentatively kept monospecific with a conical and raised style-head; the probable expansion of Treutlera to include those species with long-rostrate or hemispherical and exserted style-heads from the M. oreophila subclade and even the unsampled Sinomarsdenia with included styles needs future studies to confirm. Based on all available materials, we update the morphological description of T. insignis concerning the much variable flower colors and some errors in previous descriptions. A lectotype is newly designated for T. insignis from the mixed original material. A distribution map and color photos from field and with detailed floral dissection are provided.