Jasminum parceflorum (Oleaceae), a new species from tropical limestone habitats in Yunnan, China, is described and illustrated here. The new species is similar to J. pierreanum and J. rarum, but can be distinguished by its linear calyx lobes, dry calyces without ridges, terminal 1 (or 3)-flowered cymes and axillary solitary flowers.

Jasminum, limestone forest, Xishuangbanna

Jasminum L. (Linnaeus 1753), with about 200 species of woody climbers and erect shrubs (Green 2004), is the largest genus of the olive family. The genus is distributed throughout the Old World tropics and warm temperate regions (Green 1969, 2004), with the specific diversity center suited in tropical Asia. Within Jasminum, De Candolle (1844) divided the genus into four sections based on leaf arrangement and leaf organization, i.e., sect. Unifoliolata DC., sect. Trifoliolata DC., sect. Alternifolia DC., and sect. Jasminum (sect. Pinnatifolia DC.). Green (2001) followed De Candolle’s infrageneric classification and further added another section, i.e., sect. Primulina P. S. Green, which is characterized by the combination of opposite leaves and yellow flowers. In China, more than 40 species of Jasminum have been recorded (Chang et al. 1996, Zhang et al. 2019), of which at least 26 species can be found in limestone forests.

During a botanical expedition to Yinchang Mountain, Jinghong City, Yunnan Province, China in February 2018, we encountered an unusual species lacking flower and fruit, which possesses the most typical character states of the genus Jasminum such as opposite leaves, entire leaf margin, articulated petiole, abaxial vein axils with tufted hairs and abaxial leaf surface with glandular dots. However, based on some other vegetative characters such as laminar size, shape and vein characters, etc., the species was distinctly different from any described jasmine species in China and neighboring countries. In order to know more about its habitat and characters of its flowering and fruiting, we revisited Yinchang Mountain and adjacent areas in July 2018, July and November 2019, and collected more specimens. Subsequent detailed morphological comparisons with the similar species revealed that it represents an undescribed Jasminum species, belonging to J. sect. Unifoliolata DC. (De Candolle 1844) by having simple, opposite leaves and white flowers.

Observations and measurements of morphological characters of the new species were carried out in the field and at the herbarium, based on living individuals and specimens. Glandular dots, hairs and other tiny morphological characters were observed by using a stereomicroscope (LEICA EZ4W). Morphological comparisons with related species based on the specimens from the JSTOR Global Plants (http://plants.jstor.org/), IBK, IBSC, KUN and SYS herbaria.

Some reproductive characters, such as shape of bracts and calyx lobes, inflorescence type and position are the key taxonomic characters in distinguishing infrageneric taxa of Jasminum. The basic inflorescence type of Jasminum species is a cyme, which could form a panicle, raceme, corymb, umbel, or head. Most jasmine species have both axillary and terminal cymes, while some species only have terminal cymes, e.g., J. sambac (L.) Ait., some species usually only have axillary solitary flowers, e.g., J. nudiflorum Lindl., and other species have both axillary solitary flowers and terminal cymes, e.g., J. rehderianum Kobuski, although the terminal cymes usually reduce into solitary flowers in this new species. By having terminal 1 (or 3)-flowered cymes and axillary solitary flowers, J. parceflorum can be easily distinguished from most jasmine species. It seems to be similar to J. rarum in leaf aspect, which was treated as synonym of J. pierreanum (Green 2000). Since J. rarum differs from J. pierreanum in the shape of the leaf base (cuneate to rounded vs. more or less subcordate), and is currently known only from the type collected from Baw Re, Kanchanaburi, Thailand, further studies, particularly observations on living individuals and more specimens of J. rarum from the type locality, are needed to reconsider its taxonomic status. Here J. pierreanum and J. rarum were considered as putative closest allies, and a detailed morphological comparison between them is given in Table 1.

The authors are grateful to Mr Yuming Wang for field assistance. Thanks also go to Ms Yunxiao Liu for the line drawings. The research was funded by the National Natural Science Foundation of China (Grant Nos. U1603231, 31970206).