Elatostema qinzhouense (Urticaceae), a new species from limestone karst in Guangxi, China

Abstract

Elatostema qinzhouense L.F. Fu, A.K. Monro & Y.G. Wei, a new species from Guangxi, China is described and illustrated. Morphologically, E. qinzhouense is most similar to E. hezhouense from which it differs by having smaller size of leaf laminae, fewer and smaller staminate peduncle bracts, longer pistillate peduncle bracts and a larger achene. This result is supported by the molecular evidence. The phylogenetic position of the new species within Elatostema is evaluated using three DNA regions, ITS, trnH-psbA and psbM-trnD, for 107 taxa of Elatostema s.l. (including E. qinzhouense). Bayesian inference (BI) and maximum likelihood (ML) analyses each recovered the same strongly supported tree topologies, indicating that E. qinzhouense is a member of the core Elatostema clade and sister to E. hezhouense. Along with the phylogenetic studies, plastid genome and ribosomal DNA (rDNA) sequences of the new species are assembled and annotated. The plastid genome is 150,398 bp in length and comprises two inverted repeats (IRs) of 24,688 bp separated by a large single-copy of 83,919 bp and a small single-copy of 17,103 bp. A total of 113 functional genes are recovered, comprising 79 protein-coding genes, 30 tRNA genes, and four rRNA genes. The rDNA is 5,804 bp in length and comprised the 18S ribosomal RNA partial sequence (1,809 bp), internal transcribed spacer 1 (213 bp), 5.8S ribosomal RNA (164 bp), internal transcribed spacer 2 (248 bp) and 26S ribosomal RNA partial sequence (3,370 bp). In addition, the chromosome number of E. qinzhouense is observed to be 2n = 26, suggesting that the species is diploid. Given a consistent relationship between ploidy level and reproductive system in Elatostema, the new species is also considered to be sexually reproducing. Our assessment of the extinction threat for E. qinzhouense is that it is Endangered (EN) according to the criteria of the International Union for Conservation of Nature.

Keywords: Karst; Karyotype; Phylogeny; Plastid genome; Reproductive system; Taxonomy.

Figure 1. Plastid genome map of Elatostema qinzhouense.

The thick lines on the outer complete circle identify the inverted repeat regions (IRa and IRb). The innermost track of the plastome shows the GC content. Genes on the outside and inside of the map are transcribed in clockwise and counter directions, respectively.

Figure 2. Phylogenetic tree of Elatostema s.l. generated from Bayesian Inference (BI) of combined dataset (ITS, trnH-psbA and psbM-trnD).

Numbers on the branches indicate the posterior probability ( ≥0.5) of BI and bootstrap values (≥50%) of the ML analyses.

Figure 3. Micromorphology of achene and somatic chromosomes at metaphase of Elatostema qinzhouense.

(A) Achene from LM observation (Scale bar = 1 mm); (B) achene from SEM observation (Scale bar = 200 µm); (C) achene surface from SEM observation (Scale bar = 20 µm); (D–F) somatic chromosome observation (Scale bar = 10 µm).

Figure 4. Illustration of Elatostema qinzhouense.

(A) Habit; (B) staminate and pistillate inflorescences at subsequent nodes of monoecious stem; (C) stipule and furfuraceous stem; (D) leaves; (E) staminate inflorescence viewed from below showing involucre bracts; (F) staminate flower; (G) pistillate inflorescence viewed from below showing involucre bracts; (H) achene. Illustration by Juliet Beentje.

Figure 5. Plate of Elatostema qinzhouense.

(A) Habitat; (B) habit; (C) leave base and stipule; (D) staminate inflorescence; (E) staminate flower; (F) pistillate inflorescence. Photos by Long-Fei Fu & Bo Pan.