Tilia saxatilis Z. C. Lu & W. B. Xu, 2025

Tilia saxatilis Z. C. Lu & W. B. Xu sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 Chinese name: shí shān duàn (石山椴 View Figure 3 )

Diagnosis.

This new species is similar to Tilia tuan Szyszyl. , but differs in having leaf blades that are oblong or ovate-oblong (vs. narrowly ovate or ovate-oblong to ovate-orbicular), margins entire (vs. entire or with a few minute teeth near apex or prominently dentate); fruit ellipsoid (vs. globose or obovoid-globose), 5 - angled (vs. not ridged), apex acute (vs. rounded).

Type.

China • Guangxi: Hechi City, Du’an County, Bao’an Town, Shangzhen Village , Nongwen , around the point 24.07999417 ° N, 107.82876 ° E, limestone slope, alt. 769 m, 28 September 2023, W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17323 (holotype: IBK 00464802 ; isotypes: IBK 00464803 , IBK 00464804 , IBSC, PE) GoogleMaps .

Description.

Trees 5–15 m tall, DBH 10–80 cm. Bark dark grey; branchlets glabrous; winter buds ovoid, glabrous or slightly hairy at tip. Petiole 0.8–2 cm long, glabrous; leaf blades oblong or ovate-oblong, (3.5 –) 4.5–10 (– 14.4) cm long, 2–5.5 (– 6.2) cm wide, thickly papery, glabrous on both sides, with brown tuft domatia in vein axils of abaxial surface, lateral veins 7–8 pairs, raised on abaxial surface, reticulate veins distinct abaxially, base oblique, truncate or cordate, margins entire, apex acuminate. Cymes 5–16 - flowered, 3.5–6 cm long, peduncles glabrous. Bracts narrowly oblong, 3.8–9 cm long, 1–2 cm wide, adnate to peduncle for 1 / 3–2 / 5 of its length, glabrous or adaxially slightly hairy along mid-vein, apex obtuse, sessile. Pedicels 2–4 mm long, glabrous. Sepals 5, ovate, 4.5–5 mm long, abaxially tomentose, adaxially tomentose or with long tomentose at base. Petals oblong, 5–6 mm long, glabrous. Stamens ca. 2 mm long, glabrous; staminodes 5, slightly smaller than petals, glabrous. Ovary densely tomentose; style 1–2 mm long, glabrous. Fruit ellipsoid, 5 - angled, 8–12 mm long, 5–6 mm wide, densely appressed tomentose, apex acute; exocarp woody, hard, indehiscent. Seed ellipsoid, ca. 5 mm long.

Etymology.

The specific epithet ‘ saxatilis ’ refers to the limestone habitats of this new species.

Phenology.

Flowering July and fruiting from September to October.

Distribution and habitat.

Tilia saxatilis has only been collected from five localities restricted to central Guangxi of China. It grows sporadically in forests on limestone slopes, rare on peaks, at an elevation of 700– 950 m. The type localities are typical limestone karst landform and belong to the southern subtropical monsoon climate areas, the average annual temperature being 18–21 ° C; the annual sunshine duration is 1220–1590 hours and the annual accumulated temperature is about 6300 ° C; the annual average relative humidity is 74–80 %; the average annual rainfall is 1250–1680 mm and the evaporation is 1210–1650 mm.

Conservation status.

The new species has been found in two localities in Du’an County and three localities in Dahua County, Guangxi, China. These five localities are in the assessment area of Southwest Karst National Park, which is currently being prepared. The extent of occurrence is about 960 km 2 (<5000 km 2) and its occupancy area is predicted to continuously decline in the future due to grazing and firewood collection by local people. Therefore, according to the IUCN Red List Categories and Criteria ( IUCN Standards and Petitions Committee 2022), Tilia saxatilis should be considered in the Endangered (EN) [B 1 ab (iii)] category at present.

Additional specimens examined (paratypes).

China • Guangxi: Dahua County, Qibainong Town, Nonghe Village , Nongge , around the point 24.121001 ° N, 107.727671 ° E, limestone slope; alt. 880 m; 19 July 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 16285 ( IBK, KUN, PE) GoogleMaps • ibid.; 19 July 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 16312 ( IBK, CSH, IBSC) GoogleMaps • Du’an County, Bao’an Town, Shangzhen Village , Nongwen , around the point 24.07999417 ° N, 107.82876 ° E, limestone slope; alt. 769 m; 28 September 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17300 ( IBK) GoogleMaps • ibid.; 28 September 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17301 ( IBK, GXMG, GXMI) GoogleMaps • ibid.; 28 September 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17302 ( IBK, GXMI) GoogleMaps • ibid.; 28 September 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17303 ( IBK, GXMG, CSH) GoogleMaps • ibid.; 28 September 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17322 ( IBK, PE, KUN) GoogleMaps • Du’an County, Bao’an Town, Yuanli Village , Nongkou , around the point 24.10944 ° N, 107.811669 ° E, limestone slope; alt. 860 m; 30 September 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17367 ( IBK) GoogleMaps • ibid.; 30 September 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17368 ( IBK) GoogleMaps • Dahua County, Bansheng Town, Nongcong Village , Nongji , around the point 24 ° 13 ′ 21.75 ″ N, 107 ° 45 ′ 25.99 ″ E, limestone slope; alt. 936 m; 1 October 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17403 ( IBK) GoogleMaps • Dahua County, Qibainong Town, Nongjing Village , Baxiang , around the point 24.088763 ° N, 107.773282 ° E, limestone peak; alt. 920 m; 4 October 2023; W. B. Xu, Z. C. Lu, M. L Mo, S. L. Chang & J. Q. Huang 17503 ( IBK) GoogleMaps .

Notes.

Tilia saxatilis has glabrous branchlets, leaf blades base oblique, truncate or cordate, abaxially hairy only in vein axils, bracts narrowly oblong, adnate to inflorescence peduncle, sessile, staminodes 5 and fruits indehiscent. Based on these morphological characters, T. saxatilis is similar to T. tuan ( Tang et al. 2007) , but differs from the latter in having leaf blades that are oblong or ovate-oblong, margin entire, fruit ellipsoid, 5 - angled, apex acute. The morphological differences between T. saxatilis and T. tuan are shown in Table 1 View Table 1 .

In addition, several schemes for subdividing the genus Tilia have been described ( Chang 1989; Zhuge and Tang 1995; Pigott 2012) and, according to the different morphological characteristics, T. saxatilis would be placed in different position. Chang (1989) gave two sections for Tilia in the " Flora Republicae Popularis Sinicae "; T. saxatilis would be placed in the sect. Tilia L. based on the fruit indehiscent when dry. Zhuge and Tang (1995) divided Tilia into three sections; T. saxatilis would be placed in the sect. Lindnera Reichb. based on the woody fruit exocarp. In Pigott’s (2012) monograph, the genus Tilia was divided into four sections; T. saxatilis would be placed in the section Astrophilyra V. Engler based on the leaf blades upper surface green, glabrous, lower surface pale green, hairy only in vein axils, fruits not splitting, flowers with staminodes.