Begonia jinyunensis (Begoniaceae, section Platycentrum), a new palmately compound leaved species from Chongqing, China

Abstract

Background: Continental China is the center of Begonia species diversity in Asia and contains more than 60 species out of about 110 named species of section Platycentrum. Mt. Jinyun, located in Chongqing City at the upper reaches of the Yangtze River, harbors a subtropical broadleaved forest with high species diversity. During a botanical survey in Mt. Jinyun, an unknown Begonia species of sect. Platycentrum with palmately compound leaves was collected and studied based on detailed morphological observations and cytological and molecular phylogenetic analyses.

Results: The unknown Begonia bears a superficial resemblance to B. hemsleyana in having palmately compound leaves, a feature unseen in other species of sect. Platycentrum in China. It is however sharply distinct from the latter in the acaulous habit with aerial stems seen only at anthesis and long rhizomes (vs. erect stems to 70 cm or taller with short rhizomes), 4-6 pinnatilobed leaflets with indistinct, decurrent petiolules (vs. 7-10 serrate leaflets with distinct petiolules), and white (vs. pink) tepals. Molecular phylogenetic analyses based on nuclear ribosomal DNA and chloroplast DNA sequences indicated that this species was allied to Platycentrum species occurring in Southwest and South-central China and Vietnam, including B. hemsleyana, and clearly separable from these species. Somatic chromosome number of 2n = 22 was reported for this unknown species. The diploid chromosome number is agreeable with those published for Begonia sect. Platycentrum.

Conclusions: The unknown Begonia is confirmed to be a new species of sect. Platycentrum and hereto described as Begonia jinyunensis C.-I Peng, B. Ding & Q. Wang.

Keywords: Begonia hemsleyana; Begonia jinyunensis; Begoniaceae; Chromosome number; Flora of China; ITS; Limestone; New species; Sect. Platycentrum; rpl16.

Figure 1

Distribution of Begonia jinyunensis (Mt. Jinyun of Chongqing Municipality, Southwest China).

Figure 2

Bayesian majority-rule consensus tree with mean branch length based nrITS plus cpDNA rpl16 intron sequences. The numerals on branches are Bayesian posterior probabilities (PP, left) and bootstrap percentages (BP, right) in the MP analysis. Section designation is indicated in parentheses (Diploclinium–DIP; Platycentrum–PLA; Reichenheimia–REI; Sphenanthera–SPH). Scale bar shows the number of expected substitutions per site.

Figure 3

Somatic chromosomes at metaphase of Begonia jinyunensis (2 n = 22, Ching-I Peng 24110, HAST).

Figure 4

Begonia jinyunensis C.-I Peng, B. Ding & Q. Wang. A, Habit; B, Leaf adaxial surface; B', Leaf abaxial surface; C, Stipule; D, Staminate flower, ventral view; D', Staminate flower, lateral view; E, Stamens; F, Pistillate flower, ventral view; F', Pistillate flower, lateral view; G, Styles and stigmas; H-a,b,c, Transverse sections of developing capsule; I, Capsule. [Drawn from Ching-I Peng 24108, 24109, 24110 (HAST)].

Figure 5

Begonia jinyunensis C.-I Peng, B. Ding & Q. Wang. A, Habitat (B. jinyunensis indicated by an arrow); B, Habit; C, Rhizome; D, Staminate flower; E, Pistillate flower; F, Capsule. Scale bars are 5 cm for B, 1 cm for C and F, 5 mm for D and E. [A and C from Ching-I Peng 24109 (HAST); B, D, E, and F from Ching-I Peng 24108 (HAST)].