Thesium brevibracteatum P.C.Tam was described, based on the specimen L.C.Chiu 5128 collected from Inner Mongolia, China. It is a sub-fruticose herb up to 30 cm tall and grows on the sunny side of dunes and hills and steppes (Tam 1981, Tam 1988, Xia and Gilbert 2003, Zhao et al. 2020). In the protologue, the author indicated that T. brevibracteatum is similar to T. longifolium Turcz.(Sumnevich 1940), but is distinguished from the latter by the short bracts and long persistent perianth. As an endemic species, this species is distributed in Xilin Gol Meng, Horqin Right Front Banner and Hulun Buir, Inner Mongolia, China (Imzab 1990, Zhao et al. 2020).

The name Thesium brevibracteatum Sumnev. is validly published and described for the type (Korotkova E. E. et Titov V. S. 1502) collected from Uzbekistan (Sumnevich 1940). This species is a perennial soft-stemmed herb up to 25 cm tall. As indicated in the protologue, this species is close to T. ramosissimum Bobrov (Bobrov 1936) and T. ramosum Hayne (Hayne 1800). It differs from the first species by a very short peduncle - about 1 mm long (not 2-3 mm long), smaller nuts, non-woody roots, low and poorly-branched stems in the inflorescence area (only up to 60 cm and branched from the base) and from T. ramosum in its thin, woody roots and stems, branched in the inflorescence area, leaves with a single vein and shorter lateral bracts equal to half the length of the flower. As noted by Goloskokov (Goloskokov 1960), T. brevibracteatum Sumnev. is probably a southern, ecologically-isolated race of T. ramosum Hayne. The common distribution of the T. brevibracteatum Sumnev. is Central Asia (Western Tian Shan). It grows on the northern slopes in the upper parts of mountains on fine-grained slopes in woody and shrubby thickets (Sumnevich 1953). In addition to the type locality (Tashkent Alatau), this species was found in the Karatau mountains, Western Tian Shan (Kazakhstan) (Goloskokov 1960).

During the preparation of the checklist of vascular plants of Central Asia, we realised that the name T. brevibracteatum P.C.Tam is a later homonym of T. brevibracteatum Sumnev. (Art 53.1 of ICN, Turland et al. 2018). After checking the protologue and type specimens (Fig. 1), we determined that those two species are very different in the long peduncle and nut and the species T. brevibracteatum Sumnev. show shorter peduncle and smaller nut. This species is also different from some other species in neighbouring countries (Gubanov 1996; Krasnoborov and Malyshev 1992). In the protologue, the long persistent perianth is a key characteristic for T. brevibracteatum P.C.Tam. After checking the International Plant Name Index (https://www.ipni.org), the epithet “longiperianthium” has not previously been used for the genus Thesium. Thus, we propose the new name T. longiperianthium for T. brevibracteatum P.C.Tam.

Figure 1.  

The holotype of Thesium brevibracteatum P.C.Tam (A) and T. brevibracteatum Sumnev. (B).

We are grateful to the National Specimen Information Infrastructure (NSII) for allowing us to check the specimens online. This work was supported by the Youth Innovation Promotion Association Foundation of the Chinese Academy of Sciences (No.2019429) and Research Center for Ecology and Environment of Central Asia (RCEECA-2018-003).