﻿Lagerstroemiastenophylla (Lythraceae), a new species from China

﻿Abstract Lagerstroemiastenophylla, a new species from southeastern Shaanxi Province and northwestern Hubei Province of China is described. Morphologically, L.stenophylla resembles L.subcostata, but it differs in having 4-angular, subalate branchlets, elliptic-lanceolate, or narrowly elliptic leaves, and relatively larger flowers.


Introduction
Lagerstroemia L. (Lythraceae) is a genus of trees or shrubs with simple leaves, terminal panicles of showy flowers, and woody capsule fruits (Qin andGraham 2007, De Wilde andDuyfjes 2014).Lagerstroemia is one of the most popular ornamental flowering trees in China, producing showy flowers in summer.One such is the Lagerstroemia indica L., also known as Bairihong (百日红) in Chinese, which can bloom for up to 100 days, and is widely cultivated in China (Wang et al. 2022).In taxonomy, the monograph of this genus was completed by Koehne (1903) and fully revised by Furtado and Srisuko (1969), accepting 53 species.Thereafter, regional taxonomic revisions (Lee and Lau 1983;Hewson 1990;Qin and Graham 2007;De Wilde and Duyfjes 2013, 2014, 2016) and some sporadic taxonomic works (Zhou et al. 2004;Gu et al. 2012;Gu et al. 2015;Deepu and Pandurangan 2017;Pham et al. 2017;De Wilde and Duyfjes 2019) were published successively.In these works, many species were reduced to synonyms, and many new species were described.According to our statistics, the genus Lagerstroemia currently comprises about 51 species (excluding subspecies and varieties).
In China, there are 15 Lagerstroemia species that have been documented in "Flora of China" (Qin and Graham 2007).Lagerstroemia parviflora Roxb.was recorded in Yingjiang County of southern Yunnan Province (Yuan 1983), and L. minuticarpa Debberm.ex P.C.Kanjilal was recorded in Motuo County of Tibet Autonomous Region (Tang 1986), but neither of them was included in "Flora of China".Recently, two new species of China were discovered, including L. densa C.H. Gu & D.D.Ma (Gu et al. 2015) (Koehne 1903;Furtado and Srisuko 1969;Ho 1974;Lee and Lau 1983;Fu 2002;Zhou et al. 2004;Qin and Graham 2007;Gu et al. 2012;De Wilde and Duyfjes 2013, 2014, 2016;Li and Li 2013;Gu et al. 2015;Liu et al. 2022) were therefore conducted.Field investigation was also conducted, and more specimens were collected.The result of these studies confirmed a new Lagerstroemia species from Shaanxi and Hubei Provinces of China, which is described below, bringing the total numbers of species of Lagerstroemia to 52.

Material and methods
Morphological descriptions were based on observations of the living plants in the field and dried specimens in herbaria.Measurements were conducted manually with rulers or using Digimizer version 4.6.0(MedCalc Software, Mariakerke, Belgium), and a total of 53 collections were measured.The voucher specimens were deposited in Guangzhou Institute of Forestry and Landscape Architecture, and the herbarium of South China Botanical Garden (IBSC).Diagnosis.Lagerstroemia stenophylla is morphologically similar to L. subcostata Koehne, but distinguished by its branchlets 4-angular, sometimes subalate, leaves elliptic-lanceolate, narrowly elliptic, leaf apex acute, leaf base cuneate, flowers 2.5-3 cm in diameter.
Phenology.Flowering from May to June, and fruiting after July and fruits persist through winter.
Distribution and habitat.Lagerstroemia stenophylla is hitherto known from Baihe County, Danfeng County, Shanyang County, Shangnan County, Xunyang County, Zhashui County, Zhen'an County of south-eastern Shaanxi Province and Baokang County, Fang County and Shiyan City of north-western Hubei Province (Fig. 2).It grows on rocky slopes in ravine, at 290-770 m elevation.
Etymology.The epithet of the new species refers to its narrow leaf blade.Vernacular name.The Chinese name of the new species is here given as 狭叶紫薇 (xiá yè zǐ wēi).Note.Lagerstroemia stenophylla is formerly misidentified as L. subcostata (Li and Li 2013).Morphologically, L. stenophylla and L. subcostata share many similar characters, including calyx tubes cup-shaped, with ca. 12 ribs or darkened veins, epicalyx absent, and sepals adaxially glabrous, stamens less than 30, leading to misidentify L. stenophylla as L. subcostata, using the Keys of "Flora Reipublicae Popularis Sinicae" (Lee and Lau 1983) and "Flora of China" (Qin and Graham 2007).However, L. stenophylla is a shrub or small tree with conspicuously smaller, narrower leaves and larger flowers, differing distinctly from L. subcostata.Detailed morphological comparisons among L. stenophylla and its relatives are presented in Table 1.

Figure 1 .
Figure 1.Plate of Lagerstroemia stenophylla A habitat B flowering individuals C stems D flowering branch E fruiting branch F leaves G flower buds H flowers I petals J capsules and seeds.
from Guangxi Zhuang Autonomous Region and L. menglaensis C.H.Gu, M.C.Ji & D.D.Ma (Gu et al. 2012) from Yunnan Province.PhytoKeys 234: 127-133 (2023), DOI: 10.3897/phytokeys.234.111861Bao-Huan Wu et al.: New species of Lagerstroemia L. During our examination of Lagerstroemia specimens, some collections from south-eastern Shaanxi Province of China, such as Z.B. Wang 16543 from Shanyang County and B.Z. Guo 2225 from Xunyang County, were found likely misidentified as L. subcostata Koehne.While morphologically similar, these specimens have conspicuously smaller, narrower leaves.A more extensive examination of specimens and literature survey