Re-instatement of Sorbus harrowiana (Rosaceae), based on morphometric analysis

Abstract Sorbus harrowiana (≡Pyrus harrowiana), previously considered a synonym of Sorbus insignis (≡Pyrus insignis) in the Flora of China, is re-instated here and shown to be distinct from S. insignis, based on morphometric analysis, coupled with herbarium and field investigation. We also present for the first-time full descriptions, distributional records and notes for S. harrowiana and S. insignis.

aforementioned genera by their pinnately compound-leaves and are mainly distributed in the Northern Hemisphere: one or two species in Europe, seven species in North America and ca. 70 species throughout Asia (Hooker 1878;Warburg and Kárpáti 1968;Phipps et al. 1990;Lu and Spongberg 2003;McAllister 2005;Zika and Bailleul 2015 Sorbus insignis was first published by J. D. Hooker and C B. Clarke (Hooker 1878) in the genus Pyrus (≡Pyrus insignis Hook. f.), based on the collections from the Sikkim Himalaya. In the protologue, Hooker (1878) described S. insignis as a small, very robust tree with 4-6 paired leaflets per compound leaf and leaflet blades 3-4 inches (ca. 7-10 cm) long. Then, Hedlund (1901) transferred it to the genus Sorbus, based on its pinnately compound-leaves.
Sorbus harrowiana was described on a single George Forrest collection from the Yunnan, south-western China. In the protologue, Rehder (1920) emphasised the large leaflets which often exceed 8 inches (ca. 20 cm) in length and stated that S. harrowiana is markedly different from S. insignis, although the exact differences were not mentioned. Most taxonomists followed his opinion and considered the two to be distinct species (Yü and Lu 1974;Long 1987;Phipps et al. 1990;Kress et al. 2003;McAllister 2005;Watson and Manandhar 2012). Gabrielian (1978), however, treated S. harrowiana as a synonym of S. insignis in the taxonomic and nomenclatural works of the genus Sorbus in western Asia and the Himalayas, but gave no detailed explanation. This treatment was subsequently adopted in the Flora of China (Lu and Spongberg 2003) and Tropicos (https://www.tropicos. org). During our taxonomic research on Sorbus, we found that these two species are easily identified and distinguishable in terms of morphological characteristics and geographical distribution. Herein, we evaluate the morphological variation between S. insignis and S. harrowiana through a morphometric study of herbarium specimens to establish the delimitation and validity of the two species and to produce a taxonomic treatment including descriptions and distributional notes.

Plant material and characters scored
Herbarium specimens were studied at A, CAS, CDBI, GH, E, IBSC, K, KATH, KUN, LBG, MO, P, PE, TI and WU (abbreviations according to Thiers 2019). Leaflet length, width and length/width ratio (l/w ratio) were chosen as the morphometric variables to be measured amongst 133 specimen sheets (17 of Sorbus insignis and 116 of S. harrowiana) in 56 collections from across the range of their geographic distribution (Suppl. material 1: Table S1). Two to four compound leaves were randomly selected from each specimen. Two middle leaflets from each compound leaf were selected for measurement. A total of 1323 leaflets were measured (141 of S. insignis and 1128 of S. harrowiana).

Statistical analyses
Normality of the QN standardised variables was tested using the Shapiro and Wilk test (Mahibbur and Govindarajulu 1997), with statistically-significant differences set by the p value < 0.05. Length and width data did not fit a normal distribution, even after log 10 -or square root-transformation, with only l/w data fitting a normal distribution after log 10 transformation. As such, we performed analyses using both non-parametric Wilcoxon signed-rank tests on untransformed data and parametric Welch Two Sample T-tests on log 10 transformed data as T-tests are considered robust to non-normality when large sample sizes are used. The analyses were performed in R version 4.0.2 (R Foundation for Statistical Computing, Vienna, AT). The data matrix for analysis was prepared in Microsoft Excel 2011 and is available on request.
Phenology. Flowering May-July; fruiting Sep-Oct. Distribution and habitat. Sorbus harrowiana is distributed in China and Myanmar (Fig. 3). It grows in broad-leaved forests with an altitudinal range between 2100 and 3300 m. (Fig. 4).  Key to species in Sorbus Ser. Insignes Yü.
Note. George Forrest made seven major expeditions to western China and north-eastern Myanmar during 1917 and1931, with over 30,000 collections being made. In these expeditions, G. Forrest collected at least 23 specimens of Sorbus harrowiana, of which 15 lacked locality information. However, from limited collection information, we are able to broadly georeference these 15 specimens to four different regions (as he mentioned in the collection record), i.e. (1)