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Research Article
Indigofera jintongpenensis (Fabaceae, Papilionoideae, Indigofereae), a new species from Yunnan, southwest China
expand article infoLan Yao‡, Yan Yang‡, Xue-Li Zhao§, Qiu-Ping Wang‡, Huan-Chong Wang‡|
‡ Yunnan University, Kunming, China
§ Southwest Forestry University, Kunming, China
| Herbarium of Yunnan University, Kunming, China

Corresponding author: Huan-Chong Wang ( hchwang@ynu.edu.cn )

Academic editor: Clifford Morden
© 2024 Lan Yao, Yan Yang, Xue-Li Zhao, Qiu-Ping Wang, Huan-Chong Wang.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Yao L, Yang Y, Zhao X-L, Wang Q-P, Wang H-C (2024) Indigofera jintongpenensis (Fabaceae, Papilionoideae, Indigofereae), a new species from Yunnan, southwest China. PhytoKeys 241: 91-101. https://doi.org/10.3897/phytokeys.241.120230
Open Access

Abstract

Indigofera jintongpenensis, a new species of the subfamily Papilionoideae of Fabaceae, is described and illustrated from Yunnan, southwest China. The new species is characterised by having a prostrate habit, flexible stems and branches, as well as spreading, sub-basifixed, asymmetrically 2-branched trichomes covering the entire plant, discoid calyx, and racemose inflorescences 6–8-flowered, short, 1–2 (–3.5) cm in length, apparently shorter than the leaf. A distribution map and comparison of morphological diagnostic characters with its morphologically similar species are provided. Additionally, a preliminary conservation assessment of I. jintongpenensis is proposed following IUCN criteria.

Key words

Endemism, Indigofereae, Jintongpen Mountain, mat-forming, short inflorescence, taxonomy

Introduction

Indigofera L. is a legume genus belonging to the tribe Indigofereae of the subfamily Papilionoideae (Schrire et al. 2005; Azani et al. 2017). With approximately 750 species (Schrire et al. 2009), it is the third largest genus in Fabaceae. The genus is mainly distributed in tropical and subtropical regions worldwide with centres of species diversity primarily occurring in Africa (ca. 550 species), the Sino-Himalayan region (ca. 105 species), Australia (ca. 50 species) and the New World (ca. 45 species) (Schrire et al. 2009). Species of Indigofera are typically shrubs, but some are small trees, herbaceous perennials or annuals. The genus is characterised by a combination of the presence of medifixed 2-branched trichomes, pulvinate leaves, axillary simple racemes, anthers with appendiculate connective and flowers with an explosive pollen display (Hutchinson 1964; De Kort and Thijsse 1984). The genus includes economically important species with a variety of uses (Gerometta et al. 2020). Notably, I. tinctoria L. and I. suffruticosa Mill. are the principal sources for production of natural indigo (Zhang et al. 2019).

China harbours a high level of diversity for Indigofera species, including many endemics, with the highest species diversity found in the south-western China (Yin et al. 1992; Gao and Schrire 2010). The first comprehensive revision for Chinese Indigofera was proposed by Craib (1913), recognising 57 species with 31 newly named. In the Flora Reipublicae Popularis Sinicae, Fang and Zheng (1994) recognised 81 species and nine varieties. In the latest treatment by Gao and Schrire (2010) in the Flora of China, 79 species and nine varieties were accepted, 45 of which are endemic. Recently, Zhao and Gao (2015), Zhao et al. (2020) and Liu et al. (2022) described three additional species of Indigofera in southwest China, highlighting the need for continued field exploration and taxonomical research of the genus in this area.

During our recent field surveys in preparation for a taxonomic revision of the genus Indigofera of Yunnan Province in southwest China, we collected an intriguing prostrate plant with a densely spreading indumentum on Jintongpen Mountain of Fumin County. Its racemose inflorescences are relatively short, bearing few flowers. After conducting extensive literature surveys and comparison with related specimens, we concluded this plant does not match with any of the previously described species. Therefore, it is described herein as a new species.

Materials and methods

The study followed the normal practice of plant taxonomic survey and herbarium taxonomy. Morphological studies of the new species were based on observation of living plants and specimens collected from the type locality. Digital images available at the JSTOR Global Plants (http://plants.jstor.org/) and at the Chinese Virtual Herbarium (http://www.cvh.ac.cn/), as well the collections housed at CDBI, KUN, PE, PYU, XTBG and YUKU were examined and compared with the new species. Relevant taxonomic literature (e.g. Craib (1913); Fang and Zheng (1994); Sun (2006); Gao and Schrire (2009, 2010); Chauhan et al. (2013); Clark et al. (2015); Pignal and De Queiroz (2019)) was consulted. Morphological studies were carried out on dried material under a stereomicroscope (Olympus SZX2, Tokyo, Japan) and measurements were made using a ruler and a metric vernier caliper. Terminology followed Gao and Schrire (2010).

Taxonomy

Indigofera jintongpenensis Huan C.Wang, L.Yao & X.L.Zhao, sp. nov.

urn:lsid:ipni.org:names:77339921-1
Figs 1, 2, 3, 4

Type

China. Yunnan Province: Fumin County, Jintongpen Mountain, alt. 2,730 m, in the scrub of the limestone mountains, 10 June 2022, H. C. Wang et al. FM16943 (Holotype: YUKU!; isotypes: YUKU!)

Figure 1. 

Indigofera jintongpenensis sp. nov. A habit B fruit branch C flower (side view) D legume E style F standard G wing H keel I calyx (glabrous inside) J calyx (outside with spreading sub-basifixed 2-branched trichomes).

Diagnosis

Indigofera jintongpenensis is most morphologically similar to I. balfouriana Craib, but it clearly differs from the latter by its habit being prostrate (vs. erect), much-branched stems and branches flexible, leaves usually 7–13-foliolate (vs. 5–9-foliolate), stipules usually 5–7 mm (vs. 3–6 mm) long, inflorescences racemose, 1–2 (–3.5) cm (vs. 2–6 cm) long, 6–8-flowered, legumes 1.5–2.5 cm (vs. 2.5–4.0 cm) long, endocarp not blotched (vs. blotched).

Figure 2. 

Indigofera jintongpenensis sp. nov. A habit B a portion of branchlet showing adaxial surface of leaflets C leaves (abaxial) D branchlet E stipules F leaves and inflorescence G inflorescence H legume.

Description

Shrubs, prostrate, 10–20 (–30) cm in height. Stems much-branched, terete, slightly 4-angled when young, flexible, usually 1.0–2.5 mm in diameter. Branchlets nearly terete, flexible, 10–20 cm long, with dense spreading white and brown sub-basifixed curly and asymmetrically 2-branched trichomes. Leaves imparipinnate, 2–7 cm × 1.0–2.5 cm, 7–13-foliolate. Stipules narrowly triangular to linear, 5–7 mm long, purple when young, turning brown when old, with spreading, brown, curled and asymmetrically 2-branched trichomes. Petioles 0.2–1.0 cm long, rachis adaxially grooved, with spreading, curled, sub-basifixed, brownish-black, 2-branched trichomes. Leaflets opposite, 0.5–1.5 cm × 0.4–0.8 cm, adaxial surface green, covered with short, spreading, white, 2-branched trichomes, abaxial surface pale green, covered with long, spreading, sub-medifixed, white, 2-branched trichomes and brown, 2-branched trichomes along primary venation; mid-vein abaxially prominent and adaxially impressed, secondary veins inconspicuous; terminal leaflets obovate, apex rounded or retuse, base broadly cuneate; lateral leaflets oblong or elliptic, apex rounded, with a mucro ca. 1 mm long, base rounded or shallowly cordate; petiolules ca. 1 mm long. Inflorescences racemose, 6–8-flowered, axillary, obviously shorter than their subtending leaf, 1–2 (–3.5) cm long. Peduncles 0.2–0.5 cm long; peduncle and rachis densely covered with spreading, white and brown, sub-basifixed, curly and asymmetrically 2-branched trichomes. Bracts narrowly lanceolate to linear, revolute, ca. 2 mm long, caducous. Pedicels ca. 2 mm long, slightly curved, with densely spreading, sub-basifixed, white and brown, 2-branched trichomes. Calyx discoid, spreading, outside with spreading brown and white, sub-basifixed, asymmetrically 2-branched trichomes, glabrous inside; tube ca. 1 mm long; lobes 5, unequal, triangular-lanceolate, ca. 1.5–2.0 mm long, apex long acuminate. Corolla pink; standard obovate-elliptic, 7–9 mm × 4–6 mm, apex rounded, base broadly cuneate, outside with white, soft, 2-branched trichomes, margin ciliate; wings narrowly oblong, ca. 8 mm long, ca. 2 mm wide, base bristly, margin ciliate; keel petals 7–9 mm × ca. 1.5 mm, outside covered with spreading white trichomes towards apex, with spur ca. 1 mm long. Stamens 10, diadelphous, 9 stamens fused and the vexillary one free, 5–6 mm long; anthers ovoid, apically convex. Ovary hairy; style glabrous. Legume cylindrical, sutures thickened, 1.5–2.5 cm × ca. 0.2 cm, apex beaked, with white and brown, medifixed, symmetrically 2-branched trichomes, endocarp not blotched. Seeds 5–7 per legume, oblong to rectangle, 1–2 mm × ca. 1 mm, transverse septa present between seeds.

Figure 3. 

Holotype of Indigofera jintongpenensis (YUKU-05008413).

Phenology

Flowering from June to September, fruiting from August to December.

Figure 4. 

Indigofera jintongpenensis sp. nov. A flower (lateral view) B calyx C standard D wing E keel F pistil and stamens G stamen H seeds.

Etymology

The specific epithet “jintongpenensis” is derived from the type locality of the new species, the Jintongpen Mountain and the Latin suffix -ensis, indicating the place of origin or growth.

Distribution and ecology

According to the present investigations, Indigofera jintongpenensis is only found in its type locality, the Jintongpen Mountain of Fuming County, located in central Yunnan Province, southwest China (Fig. 5). With a maximum altitude of 2,817 m, the Jintongpen Mountain is the highest peak in Fuming County. I. jintongpenensis has been observed at elevations ranging from 2600–2817 m in the summit region of the mountain. It usually grows in the limestone scrub and its association includes Allium wallichii Kunth (Amaryllidaceae), Asparagus filicinus Buch.-Ham. ex D.Don (Asparagaceae), Berberis wilsoniae Hemsley (Berberidaceae), Buddleja myriantha Diels (Scrophulariaceae), Impatiens yaoshanensis K.M.Liu & Y.Y.Cong (Balsaminaceae), Lolium perenne Linn. (Poaceae), Quercus pannosa Hand.-Mazz. (Fagaceae), Quercus rehderiana Handel-Mazzetti (Fagaceae), Silene gracilicaulis C.L.Tang (Caryophyllaceae) and so on. It can also be found occasionally under the thickets predominated by Quercus pannosa Hand.-Mazz. (Fagaceae).

Figure 5. 

Geographical distribution of Indigofera jintongpenensis sp. nov. (red dot).

Conservation status

Indigofera jintongpenensis is a rare species with a restricted distribution and small population size. It is only known from a single locality on the Jintongpen Mountain in the Fumin County, southwest China, which is not within any protected area. The estimated area of occupancy (AOO) is less than 20 km2. The total population size is estimated to be fewer than 250 mature individuals. Following the IUCN criteria (IUCN 2022), this new species should be classified as Endangered [EN (B2abiii, D)].

Taxonomic notes

Indigofera jintongpenensis is mainly characterised by having a prostrate habit, 2-branched trichomes that are spreading and asymmetrical, and racemose inflorescences that are 6–8-flowered and relatively short (mostly 1–2 cm in length). It is most morphologically similar to I. balfouriana Craib in terms of indumentum on various parts of the plant, as well as flower shape and size, but is clearly distinguished by the features pointed out in the diagnosis as well as others (Table 1).

Table 1.
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Morphological comparison amongst Indigofera jintongpenensis and the related species.

Character I. jintongpenensis I. balfouriana I. szechuensis
Habit prostrate shrub erect shrub erect shrub
Plant height (m) 0.1–0.2 (–0.3) 0.6–2.0 0.8–2.5
Stems prostrate erect erect
Stem indumentum spreading, sub-basifixed curly and asymmetrical spreading or subspreading appressed or 2-branched appressed mixed and medifixed symmetrically
Leaf length (cm) 2–7 3–9 4–10
Stipule size (mm) 5–7 3–6 up to 2.5
No. of leaflets 7–13 5–9 (5–) 7–13
Leaflet size (mm) 5–15 × 4–8 6–20 × 4–13 5–20 × 4–9
Raceme length (cm) 1–2 (–3.5) 2–6 10–19
Peduncle size (cm) 0.2–0.5 0.5–1.5 0.8–2.7
Calyx shape discoid bell-shaped cup-shaped
Colour of corolla pink red to purple crimson-red
Standard size (mm) 7–9 × 4–6 6.0–9.5 × 5.0–6.0 7.5–9.5 × 5.0–6.5
Legume length (cm) 1.5–2.5 2.5–4.0 3.5–4.0

Indigofera jintongpenensis is also similar to Indigofera szechuensis Craib in overlapping leaf length, the number of leaflets and overlapping standard size (Table 1). However, I. szechuensis differs from I. jintongpenensis in having an erect habit, 2-branched trichomes appressed, symmetrical and medifixed, stipules 2.5 mm long, inflorescences 10–19 cm long, peduncles 8–27 mm long (Table 1).

Additional specimens examined

(Paratypes). China. Yunnan: Fumin County, Jintongpen Mountain, alt. 2770 m, 6 September 2023, H. C. Wang et al. FM22978, FM22988, FM23008 (YUKU); Fumin County, Jintongpen Mountain, alt. 2710 m, 2 November 2023, H. C. Wang et al. FM23540 (YUKU).

Acknowledgements

We sincerely thank the editor and the reviewer for their extensive suggestions to improve the manuscript.

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Funding

This research was supported by the Second Tibetan Plateau Scientific Expedition and Research (STEP) programme (2019QZKK0502) and the National Natural Science Foundation of China (NSFC) (Grant No.31960040).

Author contributions

Investigation: HCW, LY, QPW, XLZ, YY. Writing – original draft: LY. Writing – review and editing: HCW, LY.

Author ORCIDs

Lan Yao https://orcid.org/0009-0001-4326-2663

Yan Yang https://orcid.org/0009-0001-0764-8745

Xue-Li Zhao https://orcid.org/0000-0002-8773-5602

Qiu-Ping Wang https://orcid.org/0000-0001-7765-4174

Huan-Chong Wang https://orcid.org/0000-0001-8562-8849

Data availability

All of the data that support the findings of this study are available in the main text.

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