Cucumis sativus L. var. xishuangbannanensis Qi & Yuan ex S.S.Renner, 2017

Renner, Susanne S., 2017, A valid name for the Xishuangbanna gourd, a cucumber with carotene-rich fruits, PhytoKeys 85, pp. 87-94 : 88-90

Cucumis sativus L. var. xishuangbannanensis Qi & Yuan ex S.S.Renner var. nov.

Notes.

Differs from all other forms of C. sativus in producing thick-cylindric fruits that have ≥ 5 carpels and at maturity a non-bitter orange pulp (Fig. 2 ), while var. hardwickii and var. sativus both have 3 carpels and green pulp, which in var. hardwickii is bitter, in var. sativus non-bitter.

Molecular diagnosis.

Verifiable DNA differences (characters): On chromosome 3, within the physical interval that spans the ore gene, Xishuangbanna cucumbers carry asparagine, whereas all other C. sativus (37 from East Asia, 29 from Eurasia, 30 from India) and homologous proteins from ten other species of flowering plants carry alanine at this site. This amino acid change at residue 257 (p.Ala257Asp) in Csa3G183920, affects a gene encoding a putative β-carotene hydroxylase, designated CsaBCH1 by Qi et al. (2013; Fig. 3 ).

Type.

CHINA, Yunnan Province, Xishuangbanna region, Menglun, Mengla county . Farmland of the Jinuo people at 1200 m, collected in flower on 18 July 2017; young fruits photographed on 20 July 2017 to show the pulp just beginning to turn orange; Chang Yanfen 1141 (holotype: PE; isotypes; IBSC, K, KUN, L, M, MO, US, XTBG).

Distribution.

China (Yunnan), Laos, Vietnam, probably also Myanmar/Burma.

Flowering in July, mature fruits from the end of August onward (personal observation by Chang Yanfen).

Habitat, cultivation, and use.

Growing in a tropical warm, humid climate above 1000 m alt. This form of cucumber has long been cultivated by the Jinuo, Hani, and Aini ethnic groups of China, Laos, and Vietnam, who call it ‘shihuo’ ( Chen et al. 1994; Chang Yanfen, personal communication, July 2017) or 'da huang gua’ (big cucumber) and 'shan huang gua’ (mountain cucumber; Yang et al. 1991). Local farmers intercrop gourd plants with dry rice, and cultivate three regional types, called Cattle shihuo, Ivory shihuo, and Round shihuo ( Chen et al. 1994). They sow the seeds in April and harvest fruits from August to October/November. The Xishuangbanna gourd has primary stems 6-7 meters long and 20-40 lateral branches; plants are monoecious, and nodes often bear one female and one male flower ( Chen et al. 1994). A single plant can bear about 10 mature fruits with a yield of 10-20 kilograms per plant ( Chen et al. 1994). Like other cucumbers in China, the fruits are eaten raw or boiled, sliced, and spiced ( Yang et al. 1991; Chen et al. 1994).

Etymology.

The epithet was proposed by Qi et al. (1983) and refers to the geographic occurrence.

Specimens examined.

The monograph of Cucumis by Kirkbride (1993) mentions Qi et al.'s (1983) paper on the Xishuangbanna cucumber in the discussion following C. sativus (with the erroneous spelling ' xishuangbannanesis ' of the original paper), but does not formally treat the name because Kirkbride, of course, knew that the name was not valid for lack of a type and a Latin diagnosis or description. KUN has three specimens from Yunnan of which Kirkbride in 1991 annotated one as ' C. sativus ', while the other two are annotated by Chinese taxonomists as var. hardwickii . Without mature fruits (whose carpel number could be determined) or DNA sequencing, it cannot be decided whether any of these specimen might represent the orange cucumber. I have not found any herbarium specimens annotated as ' var. xishuangbannanensis ' despite numerous emails (cf. Acknowledgements).

Figures

Figure 2. Section of a mature fruit of Cucumis sativus var. xishuangbannanensis. Reproduced from Staub et al. (2011).

Figure 3. Physical position of the ore gene on Cucumis sativus chromosome 3. Blue diamonds below the seven chromosomes indicate the positions of 43 SNPs c Mutation at residue 257 changing the conserved amino acid of a putative β-carotene hydroxylase (CsaBCH 1). Xishuangbanna group cucumbers carry asparagine, whereas all other cucumbers and homologous proteins from ten other species carry alanine d CsaBCH 1 mRNA levels in Xishuangbanna cucumbers that accumulate β-carotene. Reproduced from Qi et al. (2013).