Persicaria rotunda (Z.Z.Zhou & Q.Y.Sun) Bo Li, comb. &, 2019

Guo, Yue-Ning, Chen, Shao-Feng, Chen, Ming-Lin & Li, Bo, 2019, Persicaria jucunda var. rotunda (Polygonaceae, Persicarieae), a distinct distylous taxa raised to specific rank, PhytoKeys 126, pp. 127-138 : 129-134

Persicaria rotunda (Z.Z.Zhou & Q.Y.Sun) Bo Li, comb. & stat. nov. Figures 1 , 2

Persicaria rotunda ≡ Polygonum jucundum Meisn. var. rotundum Z.Z.Zhou & Q.Y.Sun, Acta Phytotax. Sin. 45(5): 714 (713-718; figs.). 2007. Type: CHINA. Anhui Province, Dongzhi County, Shengjin Lake, on riparian plains, Alt. 6-20 m, 4 October 2006, Z.Z.Zhou 0602 (holotype: PE!, isotype: ANU).

Persicaria rotunda ≡ Persicaria jucunda (Meisn.) Migo var. rotunda (Z.Z.Zhou & Q.Y.Sun) Bo Li, Phytotaxa 91 (1): 24. 2013.

Diagnosis.

This species is easily distinguished from other Persicaria taxa by its completely decumbent leafless basal branches, almost sessile leaves, truncate, linear-lanceolate leaf blades, spicate, short and dense inflorescences, pedicels longer than bracts and dimorphic flowers and achenes. It occurs as one of the dominant species of some lakeshore plant communities in several large wetlands of northern Jiangxi and south-western Anhui provinces, eastern China.

Description.

Annual herbs. Stems slender, glabrous, basal branches 6-26, completely decumbent, 3-15 cm long, leafless, dark brown, producing numerous fibrous roots at each node; 3-12 additional flowering shoots branched from the upper nodes of each basal branch, 6-65 cm high, prostrate to erect, green to purplish-red, nodes inflated, purple. Leaves nearly sessile; leaf blades narrowly lanceolate to linear-lanceolate, 1.5-12.5 cm long, 0.3-1.3 cm wide, lateral veins 9-16 pairs, both surfaces glabrous, base round, apex acuminate, margin entire, shortly ciliate. Ocrea tubular, 4.5-11.5 mm long, membranous, sparsely appressed pubescent, apex truncate, fimbriate, cilia 2.2-5.3 mm long. Inflorescence terminal, erect, spicate, dense, 0.5-3.8 cm long; peduncle 3.5-6.5 cm long, glabrous; bracts purplish-red, funnel-shaped, sparsely pubescent, margin submembranous, shortly ciliate, each bract contains 4-7-flowers. Pedicel longer than bracts, 1.5-2.5 mm. Flowers dimorphic; perianth 5-parted, pinkish-white; long-styled flowers (called as L-morph) 3.9-4.4 mm long, stamens 8, 2.6-3.2 mm, styles 3, connate to below middle, 4.3-5.1 mm, exserted; short-styled flowers (called as S-morph) 3.7-4.2 mm long, stamens 8, 3.8-4.9 mm, exserted, styles 3, connate to below middle, 2.4-2.9 mm; stigmas capitate; nectaries 8, arranged at the base of ovary. Achenes included in persistent perianth, dimorphic; L-morph dark brown, ellipsoid, trigonous, base rounded to broadly cuneate, apex acuminate, surface opaque, densely reticular - pitted, 3.6-4.2 mm long, 2.1-2.3 mm wide; S-morph black, ovoid, trigonous, base broadly cuneate, apex acute, surface opaque, densely pitted, 2.9-3.3 mm long, 1.8-2.1 mm wide.

Phenology.

Flowering was observed from July to December and fruiting from late July to January.

Distribution and habitat.

Persicaira rotunda is currently known only from several wetlands in north of Jiangxi Province and southwest of Anhui Province, eastern China and mainly grows in marshy and grassy areas around Daguan Lake, Lihu Lake, Longgan Lake, Poyang Lake Qingcao Lake, Shengjin Lake, Shimeng Lake and Wuchang Lake, which are several small to large lakes located near the Yangtze River. It usually occurs as one of the dominant species of some lakeshore plant communities (Fig. 1A ).

Specimen examined.

CHINA. Jiangxi Province, Xingzi County, Shenling Lake, on grassy lakeside, Alt. 10 m, 29.270044N, 116.040173E, 16 July 2008, B.Li JX046 (IBSC); Jiangxi Province, Yongxiu County, Wucheng Town, Poyang Lake, in wet meadow, Alt. 14 m, 29.114364N, 116.032021E, 11 December 2017, B.Li LB0778 (JXAU); Jiangxi Province, Yongxiu County, Wucheng Town, Poyang Lake, in wetland marsh, Alt. 6 m, 29.133935N, 116.053571E, 15 October 2018, B.Li LB0901 (JXAU).

Notes.

As noted by Zhou et al. (2007), P. rotunda is most similar to P. jucunda (Fig. 3 ) in gross morphology, particularly in having uninterrupted spicate inflorescences with dense flowers and slender pedicels longer than bracts. However, the authors did not notice that both of the species are distylous, which is another important similarity between the two taxa. The distyly of P. jucunda was firstly observed and confirmed by Chen and Zhang (2010). In the present study, we confirmed that P. rotunda is also a typical distylous species. The heights of the stigmas (4.63 ± 0.191 mm vs. 2.61 ± 0.056 mm, L-morph vs. S-morph) and anthers (2.74 ± 0.092 mm vs. 4.68 ± 0.178 mm, L-morph vs. S-morph) are reciprocal in the two morphs. However, P. rotunda is clearly different from P. jucunda , not only in some morphological traits (Fig. 4 ), but also in several micro-morphological characters (Table 1 ).

Besides the differences summarised by Zhou et al. (2007), such as leaf shape, leaf width, petiole length and stem diameter, we observed several additional morphological traits that are clearly distinct between P. rotunda and P. jucunda . The stems of P. rotunda have 6-26 basal branches which are leafless and completely decumbent with numerous fibrous roots at each node. On the upper nodes of each basal branch, there are 3-12 flowering shoots which are prostrate to erect and normally bearing leaves and inflorescences (Fig. 1C ). However, the stems of P. jucunda are mostly erect or only prostrate at the base and the number of its branches are much fewer than those of P. rotunda . Persicaria rotunda also has more pairs of leaf lateral veins and much shorter inflorescences than P. jucunda (Fig. 4 ).

Though both of P. rotunda and P. jucunda have dimorphic flowers, the achenes of P. rotunda are also dimorphic, with the L-morph ellipsoid in shape and dark brown in colour, whereas the S-morph achene is ovoid in shape and black in colour (Fig. 5A ). Additionally, the L-morph achenes of P. rotunda have larger size and more raised reticulate epidermal ornamentations than those of the S-morph (Figs 5B-E ). In contrast, the achenes of P. jucunda are homomorphic with the same smooth surfaces in both morphs ( Chen and Zhang 2010). Amongst the distylous taxa reported in Persicaria , P. rotunda is, so far, the only species that shows dimorphic features on achenes.

Leaf epidermis characters have been tested to be of important taxonomic significance in Persicaria ( Hou 2006, Zhu et al. 2007, Yasmin et al. 2010). When observing the leaf epidermis of P. rotunda and P. jucunda , we found that there are significant differences in the leaf epidermal micro-morphology of the two taxa (Fig. 6 ). In P. rotunda , the adaxial leaf epidermal cells are polygonal in shape with the straight anticlinal walls and no stomatal apparatus or gland occurs on the surface (Fig. 6A ). However, the adaxial leaf epidermis of P. jucunda is covered by irregular epidermal cells with the anticlinal walls straight to curved and has mostly anisocytic or occasionally paracytic stomata and sparsely two-celled peltate glands (Fig. 6C ). On the abaxial leaf epidermis, plenty of four-celled peltate and spheroidal glands, anisocytic stomata and irregular epidermal cells with the anticlinal walls curved to sinuolate were observed for P. rotunda (Fig. 6B ), while in P. jucunda , no glands have been found, the stomata are paracytic and the anticlinal walls of epidermal cells are sinuolate to sinuate (Fig. 6D ).

In the protologue, Zhou et al. (2007) also investigated the tepal micro-characteristics of P. rotunda and P. jucunda and listed their differences: the anticlinal walls of epidermal cells are curved to sinuolate in P. rotunda , while sinuolate to sinuate in P. jucunda ; the cuticular layer has longitudinally 10-14 of sinuate striates in P. rotunda , while 12-18 straight to sinuolate striates in P. jucunda . Taking all the above morphological and micro-morphological evidence together, we think that P. rotunda represents a distinct species in Persicaria and it should not be placed under P. jucunda as a variety, but be treated as a separate species.

Figures

Figure 1. Persicaria rotunda (Z. Z. Zhou & Q. Y. Sun) Bo Li A plant community with P. rotunda B close-up view of an individual in situ C an individual showing branches D leaves E leaf base F ocrea G inflorescences. Scale bars: 1 cm (E, F, G).

Figure 2. Line drawing of Persicaria rotunda (Z. Z. Zhou & Q. Y. Sun) Bo Li A branches and inflorescences B ocrea and leaf C inflorescence D S-morph flower and its pistil E L-morph flower and its pistil F S-morph achene G L-morph achene.

Figure 3. Persicaria jucunda (Meisn.) Migo A habit B leaves C S-morph inflorescences D L-morph inflorescences. Scale bars: 1 cm (C, D).

Figure 4. Box plots of four quantitative characters, leaf length (A) leaf width (B) number of leaf lateral vein pairs (C) and inflorescence length (D) of Persicaria rotunda and P. jucunda. The boxes (rectangle region) represent the interquartile range and the whiskers (vertical line) represent the range excluding the outliers (circles). The three upper, middle and lower lines on the boxes represent the 75 %, 50 % and 25 % of the variables, respectively. The upper and lower ends of the whiskers represent the maximum and minimum values of the variable, respectively. The circles represent the single value, where the variable value exceeds 1.5 times the difference between the 75 % and 25 %.

Figure 5. Achene morphology of Persicaria rotunda A dimorphic achenes under a stereoscope B-C SEM micrograph of L-morph achene B whole view C partial view showing its epidermis sculpture D-E SEM micrograph of S-morph achene D whole view E partial view showing its epidermis sculpture. Scale bars: 500 μm (B, D); 50 μm (C, E).

Figure 6. LM micrographs of leaf epidermis of Persicaria rotunda (A, B) and P. jucunda (C, D). A, C upper epidermis B, D lower epidermis. Arrow in B shows the four-celled peltate and spheroidal glands of P. rotunda and in C indicates the two-celled peltate glands of P. jucunda. Scale bars: 500 μm.