Gleditsia saxatilis Z.C.Lu, Y.S.Huang & Yan Liu, 2021

Lu, Zhao-Cen, Huang, Zhang-Ping, Yang, Ping, Huang, Yu-Song & Liu, Yan, 2021, Gleditsia saxatilis (Fabaceae), a new species from limestone areas of Guangxi, China based on morphological and molecular evidence, Phytotaxa 508 (2), pp. 213-220 : 215-219

Gleditsia saxatilis Z.C.Lu, Y.S.Huang & Yan Liu , sp. nov. ( Figs. 2 & 3 )

Diagnosis: — Gleditsia saxatilis is similar to Gleditsia sinensis Lam. , but differs from the latter species in its habit indeciduous, winter buds globose or subglobose, apex round, petiolules glabrescent to glabrous, leaflets 2–4 pairs, leathery, both sides glabrous, racemes shorter, 2.5–7 cm long, ovary glabrous, legume slightly falcate, stipe 3–8 mm long.

Type:— CHINA. Guangxi: Liuzhou City, Liujiang County, Baipeng Township , Bie Village , in limestone evergreen broad-leaved forests, elevation ca. 130 m, 8 August 2018, Liujiang Exped. 450221180808024 LY (holotype: IBK00430264 ; isotype: IBK00430265 ) .

Description:—Trees or small trees, indeciduous, to 15 m tall. Branches grayish to light brown, glabrous, with scattered whitish lenticels. Winter buds globose or subglobose, apex round; scales few to many, light brown, imbricate. Spines robust, terete, conical, to 10 cm long, often branched. Leaves pinnate, 10–17(25) cm long; petiolules 3–5 mm long, glabrescent to glabrous; leaflets 2–4 pairs, ovate-elliptic, oblong to obovate-elliptic, 3.3–11.5 × 1.8–6 cm, leathery, both sides glabrous, reticulate veinlets conspicuously raised on both surfaces, base rounded or cuneate, margin serrate, apex acute or acuminate, mucronate. Flowers polygamous, greenish white, in axillary or terminal, puberulent racemes 2.5–7 cm long. Male flowers: 8–9 mm in diam.; pedicels 2–3 mm long; receptacle light brown, 2–3 mm long, outside pubescent; sepals 4, triangular or triangular-lanceolate, 1.5–2 mm long, both sides pubescent; petals 4, oblong, 3–4 mm long, both sides pubescent; stamens 6–8(9), 3–4 mm long, densely lanate at the middle to lower part; rudimentary pistil 1–1.5 mm long. Bisexual flowers: 9–10 mm in diam.; pedicels 2–3 mm long; sepals and petals similar to those of male flowers but longer; stamens 6–8, densely lanate at the middle to lower part; ovary glabrous; ovules numerous; stigma inflated, slightly 2-lobed. Legume compressed, 11–23 × 3.5–4 cm, slightly falcate, with slightly thick pulp, slightly swollen on both surfaces; becoming deep brown to blackish brown when dry, apex without beak, stipe 3–8 mm long; valves leathery, often farinose. Seeds numerous, brown, shiny, oblong or elliptic, 10–13 × 8–9 mm.

Distribution and Habitat: — Gleditsia saxatilis has only been collected from limestone areas of Guangxi, China ( Fig. 4). It grows sporadically in broad-leaved forests or shrubs on limestone hills, at an elevation of 120– 800 m.

Phenology: —Flowering March to May; fruiting May to October.

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

Additional specimens examined (paratypes):— CHINA. Guangxi: Longzhou County, Banbi Village , 10 November 1956, Z. J . Li 3150 ( IBK!); Longzhou County, Nonggang National Nature Reserve , 4 October 1979, Nonggang Exped. 10750 ( IBK!); ibid., 5 October 1979, Nonggang Exped. 10803 ( IBK!); ibid., 24 May 2008, Zhongzhilian-Guangxi Exped. 1041 ( IBK!); ibid., 13 November 2009, Y. S . Huang & W. B . Xu 516 ( IBK!); ibid., 18 January 2010, Y. S . Huang & W. B . Xu 529 ( IBK!). Jingxi County, Longbang District , Longla Village , 11 December 1956, Z. J . Li 3570 ( IBK!); Jingxi County, Yuexu Township , Siming Village , 17 November 1962, Z. J . Li & Q. F . Yang 1562 ( IBK!). Huanjiang County, Mulun National Nature Reserve , 21 October 1991, Dianqiangui Exped. 70009 ( IBK!); ibid., 29 August 1994, F. N . Wei & Y . Liu M0436 ( IBK!); ibid., 19 April 2012, Y. S . Huang & al. Y1296 ( IBK!); ibid., 20 April 2012, W. B . Xu & al. ML1147 ( IBK!); ibid., 21 April 2012, Y. S . Huang & al. Y1360 ( IBK!); ibid., 25 April 2012, W. B . Xu & al. ML1275 ( IBK!); ibid., 24 August 2018, Y. L . Jiang & al. 20180824001 ( IBK!). Chongzuo City, White-headed Langur Nature Reserve , 27 May 2014, W. B . Xu & Y. S . Huang CZ0909 ( IBK!). Pingguo County, Matou Township , 13 April 2018, D. R . Peng & al. 201804036 ( GXF!); ibid., 24 July 2018, K. W . Luo 201807065 ( GXF!). Bama County, Jiazhuan Township , Poyue Village , 29 May 2019, D. X. Nong & al. 451227190529011 LY ( GXMG!). Liujiang County , Baipeng Township , Bie Village , 4 April 2019, Liujiang Exped. 450221190404041 LY ( IBK!); ibid., 14 April 2020, Liujiang Exped. 450221200414015 LY ( IBK!). Yizhou City, Xizhu Temple, 13 September 2020, P . Yang LZC219 ( IBK!) .

Discussion: — Gleditsia saxatilis can easily distinguished from the other species of Gleditsia in its habit indeciduous, leaflets pairs less, only 2–4 pairs, leathery and the shape of the leaflets. Phylogenetic analyses show that Gleditsia saxatilis closely related with Gleditsia sinensis and Gleditsia rolfei ( Fig. 1 ), but Gleditsia saxatilis differs the latters from some special characters. The morphological differences of these three species are summarized in Table 2. The identification key to the species of Gleditsia in China is provided below.

1a. Leaflets 6–24 mm long, margin entire, upper leaflets smaller than those in lower part; legume 3–6 cm long, with 1–3 seeds.......... ..................................................................................................................................................................................... G. microphylla

1b. Leaflets more than 25 mm long, margin irregularly serrate; legume more than 6 cm long, with numerous seeds.

2a. Leaflets obliquely oblong or rhombic-lanceolate, midvein conspicuously inclined at base.

3a. Leaves pinnate or bipinnate; racemes often comprising panicles; legume 6–12 cm long ................................................ G. australis

3b. Leaves pinnate; racemes simple; legume 13.5–26 cm long.

4a. Leaflets obliquely elliptic to rhombic-oblong, 2–7(12) × 1–3(5) cm; legume 13.5–26 cm long, straight or slightly curved, occasionally twisted.................................................................................................................................................................. G. fera

4b. Leaflets obliquely oblong, 2.5–3 × 1–1.5 cm; legume 18–20 cm long, slightly falcate ........................................................ G. rolfei

2b. Leaflets ovate, ovate-lanceolate or oblong, midvein at middle or slightly oblique.

5a. Leaflets 11–18 pairs, elliptic-lanceolate; ovary tomentose .......................................................................................... G. triacanthos

5b. Leaflets 2–10 pairs, elliptic, ovate or ovate-lanceolate to oblong; ovary glabrous or only sutures and base pubescent.

6a. Spines flat at least at base; leaflets with reticulate veinlets obscure, margin entire or sparsely shallowly crenate; ovary glabrous; legume flat, irregularly twisted or curved, falcate............................................................................................................. G. japonica

6b. Spines terete; leaflets with reticulate veinlets adaxially conspicuously raised, margin serrate; ovary pubescent at base and along sutures or glabrous; legume thick, not twisted, straight, curved or slightly falcate.

7a. Deciduous; winter buds conical, apex acute; leaflets (2 or) 3–9 pairs, ovate-lanceolate to oblong, papery, abaxially slightly pubescent on midvein, adaxially puberulent; racemes 5–14 cm long; legume straight or twisted .................................... G. sinensis

7b. Indeciduous; winter buds globose or subglobose, apex round; leaflets 2–4 pairs, ovate-elliptic, oblong to obovate-elliptic, leathery, both sides glabrous; racemes 2.5–7 cm long; legume slightly falcate .............................................................................. G. saxatilis

Figures

FIGURE 1. The best ML tree from the analyses of combined ITS and chloroplast trnL-F region. BI posterior probability/ML bootstrap support values (>0.5 or 50%) are shown below or above the branch around the corresponding node. G. saxatilis is highlighted in bold and red.

FIGURE 2. Gleditsia saxatilis A. Habit. B. Flowering branches. C. Fruiting branches. D. Winter buds. E. Branch. F. Spines. G. Leaves in adaxial view. H. Leaves in abaxial view. I. Trunk (shows where the spines grow).

FIGURE 3. Gleditsia saxatilis A. Male racemes. B. Bisexual racemes. C. Male flower in frontal view. D. Bisexual flower in frontal view. E. Male flower removed stamens in ventral view. F. Male flower removed stamens in abaxial view. G. Male flower in ventral view. H. The stamens from a male flower. I. Legume. J. Opened legume show seeds. K. Seeds.