Taxonomic notes on the genus Itea (Iteaceae)

Zhu-Qiu Song; Bu-Yun Zhang

doi:10.3897/phytokeys.239.117851

Abstract

The genus Itea (Iteaceae) is recognised as a genus with about 21 extant species of shrubs and trees. Within the genus, most species have oblong to elliptical leaves. The lanceolate and obolanceolate leaves are only found in three species, vix Itea amoena Chun, Itea riparia Collett & Hemsl. and Itea tenuinervia S. Y. Liu. The results of our examination of literature, specimens and living plants in the wild have shown that Itea tenuinervia is conspecific with Itea riparia and is here reduced to a synonym of the latter species. The morphological description, colour pictures, voucher specimens, distribution map of Itea riparia and its related Itea amoena, together with the morphological comparisons between the two species, are provided in this study.

Key words

China, lectotypification, synonym, taxonomy

Introduction

Itea L. (Iteaceae) was first described based on the species I. virginica L. from eastern North America (Linnaeus 1753) and later it was reported in Asia, for example, I. macrophylla Wall. from tropical Asia (Wallich 1824), I. nutans Royle from western Himalaya (Royle 1835) and I. japonica Oliv. from Japan (Oliver 1865). Itea was previously divided into two sections based on its deciduous character, i.e. sect. Deciduae Engl. (= sect. Itea) and sect. Sempervirentes Engl. (Engler 1891). The former section comprises only two species with deciduous leaves, I. virginica and I. japonica, and the latter includes the other species with evergreen leaves. Recently, Choristylis rhamnoides Harv. (Harvey 1842) from southeastern Africa was transferred to Itea as the third section, i.e. sect. Choristylis (Harv.) Jordaan (Kubitzki 2007; Jordaan 2012). Thus, Itea was considered as an unusual genus with an East Asian-eastern North American-southeastern African disjunction pattern (Kubitzki 2007; Tian et al. 2021). The genus comprises about 21 extant species of shrubs and trees, including one in Africa, one in North America and 19 species in temperate, subtropical and tropical Asia (Tian et al. 2021; POWO 2023).

The leaf shapes of the genus Itea are usually oblong to elliptical, while the lanceolate and oblanceolate leaves only appear in three species, including I. riparia Collett & Hemsl. (Collett and Hemsley 1890), I. amoena Chun (Chun 1934) and I. tenuinervia S.Y. Liu (Liu 2001; Tian et al. 2021). Itea riparia was first published based on specimens collected on river-banks from Shan Hills, southern Shan States, Myanmar and it was characterised by narrow leaves, straight branches and erect racemes (Collett and Hemsley 1890). Gagnepain (1916) originally described I. thorelii based two gatherings from Vietnam and Laos and considered that it is very similar to I. riparia, but is different from the latter in the leaf width, the shape of anthers and the length of inflorescence, flower, stamen and ovary. Craib (1931) observed that some specimens of I. riparia from Thailand match I. thorelii in some respects. In China, I. riparia was recorded in Yunnan and I. thorelii was reported in Yunnan and Guangxi (Wu 1977; Fang and Qin 1985; Jin 1995), but the two species were merged in the Flora of China due to absence of obvious different characters (Jin and Ohba 2001). The earlier name I. riparia was adopted as its accepted name (Jin and Ohba 2001; Esser 2005; Chen and Liu 2015). The species grows on river-banks or near streams.

Chun (1934) described another Itea species with narrow leaves, Itea amoena, based on specimens from southern Guangxi, China and noted that it is well characterised by narrow, long-acuminate leaves and by long lanceolate calyx lobes. The species was previously identified as “Itea riparia var. auminata Hu var. nov.”, based on Ren-Chang Ching 8059 (Chun 1934) and recognised as “Itea lanceolata Merr. n. sp.” based on Kuan-Kwang Tsoong 1868 (Jin 1995). However, the latter two names have never been validly published. This species grows near streams, just like I. riparia (Fig. 5). Besides the habitat, I. amoena and I. riparia are also similar in the habit of evergreen shrubs, the lanceolate leaves and terminal inflorescences. Liu (2001) described Itea tenuinervia on the basis of a flowering collection found near streams in Shuolong Town, Daxin County, southwestern Guangxi, i.e. Shou-Yang Liu 2893 (Fig. 1A) and it was morphologically compared with I. riparia and I. thorelii in the protologue. However, our examination of literature and specimens showed that there are no obvious differences between I. tenuinervia and I. riparia (including I. thorelii). Thus, this study treats Itea tenuinervia as a new synonym of I. riparia and discusses the morphological differences between I. riparia and I. amoena.

Figure 1.

Itea riparia A isotype of Itea tenuinervia (Shou-Yang Liu 2893, IBK00190789, https://www.cvh.ac.cn/spms/detail.php?id=c1cf1dd4) B topotype of Itea tenuinervia (Shou-Yang Liu F000749, GXMI014126), showing two divergent carpels per fruit C specimen of Itea riparia from Myanmar (J. H. Lace s.n., E00397667, https://data.rbge.org.uk/herb/E00397667), showing two divergent carpels per fruit D lectotype of Itea thorelii (Thorel 3474, P00709632, https://science.mnhn.fr/institution/mnhn/collection/p/item/p00709632), showing two divergent carpels per fruit.

Materials and methods

The specimens of the genus Itea kept in the Herbaria HITBC, IBSC and KUN have been examined by visiting these Herbaria and the images of Itea specimens deposited in the Herbaria E, GXMG, GXMI, IBK, IMDY, L, MW, N, NAS, NF, P, PE, SZ, TCD and US were also studied through the databases of specimens, such as Chinese Virtual Herbarium (CVH, https://www.cvh.ac.cn), Global Biodiversity Information Facility (GBIF, https://www.gbif.org), RBGE Herbarium Catalogue (https://data.rbge.org.uk/search/herbarium/), Naturalis BioPortal (https://bioportal.naturalis.nl/), Muséum National D'Histoire Naturelle (https://science.mnhn.fr/all/search) and Smithsonian National Museum of Natural History (https://collections.nmnh.si.edu/search/botany). Acronyms for the herbaria follow the Index Herbariorum (Thiers 2023). We also observed the living plants of the relevant species in the wild, including in the type localities of I. tenuinervia and I. amoea, as well as multiple localities of I. riparia.

Taxonomic treatment

1. Itea riparia Collett & Hemsl., J. Linn. Soc., Bot. 28: 57. 1890.

Figs 1, 2, 3, 4

= Itea thorelii Gagnep., Notul. Syst. (Paris) 3: 222.1916. Type. Laos. Luang-prabang, 1866–1868, Thorel 3474 (lectotype: P00709632, photo!, designated by Lecompte 1965: 40; isolectotypes: P00709633 photo!, P00709634 photo!).

= Itea tenuinervia S. Y. Liu, Guihaia 21(1): 35. 2001. Type. China. Guangxi Province, Daxin County, Shuolong Town, by stream, 14 Jan 2000, Shou-Yang Liu 2893 (holotype: GXCM; isotype: IBK00190789!), syn. nov.

Type

Myanmar. Southern Shan States, Shan hills, on river-banks, 2000–4000 feet (ca. 700–1400 m) elev., H. Collett s.n. (holotype, K).

Description

Shrub, evergreen, usually 0.5–2 m tall, sometimes up to 7 m. Stipules subulate, 0.2–0.7 mm long, caducous. Leaves alternate, both surfaces glabrous, chartaceous, lanceolate or oblanceolate, 3.5–13 cm long, 1–5 cm wide, length/width ratio is 2.6–5.2 (mean = 3.6), acute or slightly acuminate at apex, cuneate at base, distantly shallowly subglandular crenate-serrate along upper margin; mid-vein raised on both surfaces, lateral veins in 4–7 pairs, arcuate ascending, lateral and reticulate veins visible and impressed above surface; petiole 0.4–1.2 cm long, raised above. Pseudoracemes, terminal or sometimes also axillary, usually solitary, sometimes with short branches at base, 4–18 cm long, rachis puberulous, usually 2- or 3-flowered per node; bracts at base of pedicel, subulate, 2–3 mm long, 0.3–0.5 mm wide, deciduous. Flowers white; pedicel erect, puberulous, 3–11 mm long; calyx shallowly cupular; calyx lobes 5, triangular, green, 1.5–2 mm long, 1.2–1.5 mm wide at base, puberulous; petals 5, white, triangular-lanceolate, acute at apex, widest at base, ca. 5 mm long, 1.5–1.9 mm wide at base, glabrous, erect-spreading at anthesis, becoming green and thickened at fruiting; stamens 5, alternating with the petals, shorter than petals, 3.3–3.6 mm long; filaments glabrous, ca. 0.8 mm wide; anthers oblong, ca. 0.6 mm long, 0.4 mm wide; floral disc annular, fleshy, slightly yellow; ovary semi-inferior, consisting of two carpels diverging in the middle and united at the top; stigma capitate. Capsule glabrous, 5–8 mm long, consisting of two obviously divergent carpels, with persistent sepals and petals, turning brown and dehiscing along the ventral suture at mature. Seed numerous, white at immature and brown at mature, 1–1.7 mm across; testa slightly granular.

Distribution

The species is distributed in China, Laos, Myanmar, Thailand and Vietnam (Fig. 6). It usually occurs near streams under forests, with elevation range from 200 to 1400 m.

Specimens examined

China. Guangxi: Daxin, 15 May 2008, Guangxi Exped. Inst. Bot. 498 (IBK00278403), 17 Sept 2004, Shou-Yang Liu F000749 (GXMI014126), 400 m elev., 9 Jun 2023, 22.854261°N, 106.725634°E, Zhu-Qiu Song et al. JZ20230549 (IBSC); Jingxi, 457 m elev., 30 June 2013, En-De Liu 3996 (KUN1241727), 500 m elev., 10 May 2023, 22.991658°N, 106.674116°E, Bu-Yun Zhang et al. JZ20230371 (IBSC), 500 m elev., 9 Jun 2023, 23.009193°N, 106.659319°E, Zhu-Qiu Song et al. JZ20230553 (IBSC); Napo, 450 m elev., 18 May 1943, Pu-Chin Tsoong & Ko-Zen Kuang 356 (PE00865551, PE00865552), 15 Apr 1977, Yuan Lin et al. 3-5104 (GXMI014127, GXMI014128). Yunnan: Cangyuan, 700 m elev., 29 May 1974, Yan-Hui Li 11737 (HITBC015745, HITBC015750, IBSC0273493, KUN0477791, KUN0540565, KUN0540567), 790 m elev., 15 May 1979, Yan-Hui Li 20907 (HITBC015744, HITBC015751, KUN0540559, KUN0540568); Jinghong, 540 m elev., 7 May 1955, Kuo-Mei Feng 20754 (IBSC0273491, KUN0477788, KUN0477789, PE00865549, SZ00179768), 30 Aug 2019, Yun-Hong Tan ML56 (XSBN002276); Malipo, 1100 m elev., 21 Jun 1940, Chi-Wu Wang 86321 (KUN0477792, PE00865553), 1000 m elev., 3 Feb 1940, Chi-Wu Wang 86599 (KUN0477790); Mengla, 17 Jan 1976, Lai-Yun Xiao 11269 (HITBC099861, IBSC0273492), 680 m elev., 18 Dec 1986, Shao-Rong Guo 592 (IMDY0008066), 850 m elev., 11 Feb 1960, Yan-Hui Li 2813 (HITBC015743, IBK00170997, IBSC0273495, KUN0477787), 560 m elev., 14 Apr 1961, Yan-Hui Li 3049 (HITBC015746), 11 May 1961, Yan-Hui Li 3222 (HITBC015747, IBSC0273494, KUN0477785), Jun 1967, Yunnan First Section 138 (PE00865550), 600 m elev., 2 Sept 2023, 21.989364°N, 101.368001°E, Zhu-Qiu Song et al. JZ20231022 (IBSC); Zhenkang, 12 Apr 1976, Yan-Hui Li 20116 (HITBC015748, HITBC015749, KUN0477786). Laos. Champasak: Paksong, 29 Apr 2013, Hang Sun et al. sunhang16056 (KUN1256568, KUN1256569); Luang Namtha: Nateuy, 1130 m elev., 21 Apr 2006, En-De Liu 1686 (KUN1204594); Luang Prabang: 1866–1868, Thorel 3474 (P00709632, P00709633, P00709634); Phongsal: 30 Apr 1993, Guo-Da Tao et al. 930162 (HITBC059236, HITBC059244); Vientiane: Mt. Phu Kao Kwai, 700–800 m elev., 31 Dec 1993, N. Fukuoka & H. Koyama L-65039 (L4134635); Without precise locality, H. Bon s.n. (P03179260). Myanmar. Maymyo: 760 m elev., 21 Apr 1916, A. Rodger 510 (NAS00337458), 1066 m elev., 8 May 1912, J. H. Lace 5802 (E00397666), 1066 m elev., 4 May 1912, J. H. Lace s.n. (E00397667); Taunggyi: 1219 m elev., Apr 1939, F. G. Dickason 8273 (E01033109). Thailand. Chaiyaphum: Phu Khieo, 600–700 m elev., 1972, K. Larsen et al. 31288 (L1861211), Ban Nam Phrom, 600 m elev., 24 May 1974, R. Geesink et al. 6886 (L1861215, P00392452); Chiang Mai: Thawatchai, Kasem, 700 m elev., 7 May 1991, Guo-Da Tao et al. 653 (KUN0540552), Me Ka Pak Bank, 1300 m elev., 21 Apr 1928, H. B. Garret 505 (L1861224, L1861225, P03179261), Mae Rim District, 600 m elev., 12 Jun 2009, J. F. Maxwell 09-162 (L2058714, P00911865), Doi Sutep, Mae Sa Falls, 10 Apr 1989, J. F. Maxwell 89-446 (L1861217), Doi Intson National Park, 650 m elev., 4 May 1997, J. F. Maxwell 97-443 (L4160466), Doi Inthanon, 1400 m elev., 3 Jan 1975, R. Geesink et al. 8048 (L1861214, P03371228), Doi Inthanon, 920–960 m elev., 21 Jul 1988, S. Tsugaru T-61686 (L4161221), 18 Aug 1970, Voravut 8 (L1861218); Kanchanaburi: Sangklaburi, Toong Yai Narssuan Wildlife Reserve, 200 m elev., 12 Jan 1994, J. F. Maxwell 94-10 (L4134592), near Khwae Noi River, Pompee Village, 250 m elev., 25 Mar 1968, C. F. van Beusekom & C. Phengkhlai 108 (L1861220), 800 m elev., 30 Apr 2004, M. van de Bult 796 (L4160559); Nakhon Ratchasima: Khao Yai, 800 m elev., 25 Mar 1968, B. Hansen et al. 11340 (L1861219, L1861221); Phrae: Mae Bhaem stream, 440 m elev., 5 Jan 1972, C. F. van Beusekom et al. 4661 (L1861223); Tak: Pha Charoen Waterfall National Park, 20 June 2005, Pooma et al. 5329 (L4160075), Lansang National Park, 600 m elev., 21 Jul 1973, G. Murata et al. 16617 (L1861212, P03179258), Lan Sang National Park, 250–400 m elev., 30 Aug 1967, M. Tagawa et al. 8558 (L1861213), Larn Sarng Nat. Park, 350 m elev., 29 May 1973, R. Geesink et al. 5532 (L1861222, P03179259); Without precise locality, Apr 1921, A. F. G. Kerr 5273 (TCD0016587), Mar 1924, A. F. G. Kerr 8763 (TCD0016588). Vietnam. Dak Lak: Lak, Chu Yang Sin National Park, 900 m elev., 23 Mar 2013, M.S. Nuraliev 724 (MW0738997); Hoa Binh: Yen Thuy, Cuc Phuong National Park, 12 Sept 2002, M. V. Xinh MVX 241 (L1861216), Barrage de Cho-bo (Rivière Noire), sur les roches calcaires atteintes par les hautes eaux, 18 Oct 1888, Balansa 3152 (P00709635).

Taxonomic notes

In the protologue, Liu (2001) considered that I. tenuinervia is distinguished from I. riparia in the height (1–2 m vs. 6 m), leaf shape (long elliptical, rarely oblanceolate vs. oblong, elliptical to lanceolate), pedicel length (10 mm vs. 3–5 mm) and petal length (6 mm vs. 4 mm) and it is distinguished from I. thorelii in the leaf shape (long elliptical, rarely oblanceolate vs. oblanceolate), inflorescence type (racemes vs. racemose panicles), bract shape (triangular-lanceolate vs. linear-lanceolate), petal shape (narrowly lanceolate var. oblong-triangular) and pedicel length (10 mm vs. 4–6 mm). Subsequently, the species was accepted by Chen and Liu (2015). However, our examination of literature and specimens showed that there are no obvious differences between I. tenuinervia and I. riparia (including I. thorelii) in the characters above (see Table 1, Fig. 1). In the protologue, Liu (2001) did not describe the fruits of I. tenuinervia, but he collected a fruiting gathering at the type locality in 2004, i.e. Shou-Yang Liu F000749, which shows two obviously divergent carpels per fruit (Fig. 1B). The fruits with two obviously divergent carpels are very special in the genus Itea, because most species bear two partly or completely fused carpels before dehiscence (Jordaan 2012) and only Itea riparia (including I. thorelii) was found to have two obviously divergent carpels (see Lecompte (1965: Pl. IV 8–10); Wu (1977: Pl. 26)). Thus, in the fruit character, I. tenuinervia is very similar to I. riparia as well. Furthermore, our observations of living plants in the wild, including in the type locality of I. tenuinervia, also showed that I. tenuinervia is consistent with I. riparia in the morphological characters and habit (Figs 2–4).

Table 1.

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Comparison between Itea tenuinervia and Itea riparia.

Characters	Itea tenuinervia	Itea riparia
Habit	shrubs 1–2 m	shrubs 1–6 m tall
Branchlet	green, striate, glabrous	yellow-green, striate, glabrous
Leaf arrangement	alternate, usually crowded at upper and lower parts of branchlets	alternate, usually crowded at apex of branchlets, subclustered
Leaf texture	thinly leathery	thinly leathery
Leaf hairiness	glabrous	both surfaces glabrous
Leaf shape	long elliptic, rarely oblanceolate, base cuneate, apex acuminate, margin incurved glandular dentate	elliptic to lanceolate or obovate-elliptic, base cuneate, apex acute or acuminate, margin curved cartilaginous glandular dentate
Leaf size	5–9 × 1.7–2.2 cm	5–13 × 1.5–5 cm
Lateral veins	4–5 pairs, confluent near margin, raised abaxially, slightly sunken adaxially	4–7 pairs, arcuate, confluent near margin, slightly raised abaxially, obscure adaxially
Tertiary veins	invisible above and visible below	reticulate, invisible above
Petiole	5 mm, glabrous	4–12 mm, glabrous
Stipules	ca. 1.5 mm long, caducous	0.2–0.7 mm long
Inflorescence	racemes terminal, 8–14 cm; rachis puberulous; flowers numerous, rather crowded, often 2–3-clustered	racemes terminal, 4–18 cm; rachis puberulous; flowers numerous, rather crowded, often 3-clustered
Bracts and bracteoles	bracts triangular-lanceolate, 3–5 mm; bracteoles 1–1.5 mm long	bracts ca. 3 by 0.5 mm, caducous, bracteoles to 1 mm long, similar
Pedicels	(6–) 10 mm	3–6 mm, puberulous
Calyx	shallowly cupular; lobes triangular, ca. 2 mm	shallowly cupular; lobes erect at anthesis, triangular-lanceolate, 1.5–4 mm
Petals	5, white, sometimes slightly pink, narrowly lanceolate, ca. 6 mm long, erect at anthesis	5, white, distinctly larger than the sepals, 4–5 by 1.5–2 mm, erect
Stamens	5, situated opposite the calyx lobes; filaments 5 mm long, slightly wider below the middle, glabrous; anthers ovoid, dorsifixed.	5, situated opposite the calyx lobes; filaments 2.5–3 mm long, glabrous; anthers ca. 1 mm long, dorsifixed, ovoid.
Disc	Ring-like, yellow	Ring-like
Ovary	semi-inferior, consisting of two carpels diverging above the base at the end of flowering, with a capitate stigma	superior or semi-inferior, glabrous, consisting of two carpels diverging in the middle and united at the top in a short style, surmounted by a capitate stigma
Fruit	capsules ovoid-conical, with very divergent carpels, except at the base; dehiscence by a slit corresponding to the ventral suture (based on a topotype, Shou-Yang Liu F000749, Fig. 1B)	capsules ovoid-conical, ca. 5 mm, glabrous, with very divergent carpels, except at the base; dehiscence by a slit corresponding to the ventral suture
Phenology	Fl. Jan., fr. Sept.	Fl. and fr. May–Feb.
Distribution	Guangxi, China	Myanmar, Thailand, Laos, Vietnam, China (Guangxi, Yunnan)
References	Liu (2001)	Lecompte (1965), Jin and Ohba (2001), Esser (2005)

Figure 2.

Itea riparia from Jingxi County, Guangxi, China A habitat B–C terminal inflorescences D leaves in adaxial and abaxial views E inflorescences F flowers with the different parts separated G infructescence, showing two divergent carpels per fruit and persistent sepals and petals H fruits and seeds. Voucher specimens: Bu-Yun Zhang et al. JZ20230371 (fl., IBSC), Zhu-Qiu Song et al. JZ20230553 (fr., IBSC). Scale bars: 2 cm (B, D); 5 mm (F); 1 cm (H).

Figure 3.

Itea riparia from Daxin County, Guangxi, China A habitat B leaves in adaxial and abaxial views C fruiting branchlets D infructescence E fruits, showing two divergent carpels per fruit and becoming green and thickened petals and persistent sepals and petals. Voucher specimens: Zhu-Qiu Song et al. JZ20230549 (IBSC). Scale bar: 2 cm (B).

Figure 4.

Itea riparia from Mengla County, Yunnan, China A habitat B habit C leaves D fruiting branchlet E part of infructescence F fruits and seeds, showing two divergent carpels per fruit. Voucher specimens: Zhu-Qiu Song et al. JZ20231022 (IBSC). Scale bars: 2 cm (C); 5 mm (F).

2. Itea amoena Chun, Sunyatsenia 1(4): 238. 1934.

Fig. 5

Type

China. Guangxi Province, Shangsi County, Shup-man-tai Shan [Shi Wan Da Shan], in shaded ravine, about 1200 ft. (ca. 400 m), 29 Jul 1933, Ching-Lieh Tso 23439 (lectotype, designated here: IBSC0004326, isolectotypes: IBSC0004324, IBSC0004325, PE00864804).