Stellaria bengalensis Sindhu Arya & Harsh Singh, 2024

Sindhu, Arya & Singh, Harsh, 2024, A new species of Stellaria (Caryophyllaceae, Alsinoideae, Alsineae) from Eastern Himalaya, India, Phytotaxa 668 (2), pp. 177-185 : 178-183

Stellaria bengalensis Sindhu Arya & Harsh Singh sp. nov. ( Figs. 1–5 ).

Type: — INDIA. West Bengal: Kalimpong district, Sangsera forest range 27.1282526 N, 88.5065675 E, 20 th October 2022, Arya & Harsh Singh 2723 (Holotype: UCBD!, isotypes: RO!, UCBD!).

Diagnosis: — Stellaria bengalensis is similar to S. media from which it differs by the bract (absent vs. present in S. media ), shape and length of sepal (broadly ovate, 1.5 mm vs. ovate to lanceolate, 4 mm), flowers (zygomorphic vs. actinomorphic), petals (fused till the apex vs. fused till the half of the petal length), number of stamens and colour of anthers (4 stamens, anthers pink vs. 8–10 stamens, anthers creamy-yellow), shape and size of capsule (ellipsoid, up to 3 mm vs. ovoid, up to 8 mm), seed surface architecture (tubercles pointed with less papillae vs. tubercles short flat topped with abundant papillae), pollen morphology (frequency of pores 4–5, pore margin depressed, ektexinous body 4–5 fused vs. visible frequency of pores 8–9, pore margin elevated, ektexinous bodies numerous, free).

Description:—Annual herbs, 8.0– 10.5 cm; roots tuberous, fusiform, thick. Stem 7.5–9.6 cm tall, prostrate to ascending or erect, terete, basally branched, sparsely pubescent towards the base, nodes prominent, roots arises from the nodes, internodes ca. 2 cm long, with a single line of trichome. Leaves petioled (petiole 2.0– 3.5 cm long), median leaves cauline larger, oblanceolate or elliptic, the upper-most ones forming a rosette narrowly oblanceolate or ovate; blade (1.2–1.8 × 1.1–1.5 cm), margin entire, often wavy, apex acuminate, base obliquely cordate to reniform, abaxially midvein prominent, adaxially midvein impressed, margin shortly ciliate; stipules caducous. Inflorescence (cymes) terminal or axillary solitary flowers. Flowers white, 5-merous, 2–3 mm in diameter, 1–2 in pair, peduncles glandularciliate; bracteoles lanceolate to elliptic 1.0– 1.5 mm long, acute apex, ciliate along margins; peduncle slender, erect to spreading, up to 5 mm long, bracts absent; sepal lanceolate-oblong-ovate (2.0–2.5 × 0.7–0.8 mm), outer surface densely pubescent, green; petal 5, shorter than the sepals; stamen 4–5 shorter than petals, 1.5–2.5 mm long with filaments 1.0– 1.2 mm long, gradually narrowed upwards, not fused at base, and anthers oblong to orbicular-oblong, 0.3–0.4 mm long; ovary broadly ellipsoid-ovoid, 0.8–1.0 × 0.6–0.7 mm; styles 3, linear, stigmas curved trifid. Capsule ellipsoid, 1.2–1.6 × 0.4–0.6 mm, dehiscing with 5 valves, double the persistent sepals. Seed 2–6 per capsule,reniform, 0.7–0.9 × 0.5–0.6 mm, black-brown.

Pollen morphology (micro-morphology): —Pollen grains are spheroidal (10.77–12.26 µm in diameter), pantoporate with 4–6 visible frequency of pores. Pore margin or aperture is faintly demarcated or depressed and the diameter of each pore is 1.5–2.6 µm. The surface of the pollen is micro-echinate where as echines scattered throughout the surface often fused. Ektexinous bodies present inside the pore, minute, 4 or 5, fused ( Fig. 3 ).

Seed morphology (micro-morphology): —Seeds are reniform in shape with base circular (0.722 –0.957 × 0.520 – 0.665 mm) and margin with tubercles pointed and circular papillae concentrated on the arms of the tubercles. Densely scattered mammillate ornamentation is observed throughout the tubercles ( Fig. 4 ).

Etymology:— The specific epithet ‘ bengalensis’ corresponds to the state West Bengal which is the type locality of the new species.

Distribution and habitat:— Stellaria bengalensis is known only from Sangsera forest range, Kalinpong district of West Bengal where it grows in muddy soil slopes at 2245–2450 m a.s.l.

Flowering and fruiting times: May to September.

Conservation status:— The plant propagates mainly vegetatively. Number of individuals are very few and prone to severe grazing and human activities. We counted 20–40 scattered individuals per population (5 populations). Each population occupies an small area (less than 1 m 2). Since only a few seasons were observed and the chances of occurrence of population in other parts of western Himalayas are possible, therefore we decided for the moment to assess Stellaria bengalensis as DD (Data Deficient) following the IUCN Red list criteria (IUCN 2024).

Notes:— The new species of Stellaria bengalensis shows a morphology agreeing with that of the taxa belonging to the S. media aggregate (see e.g., El Mokni et al. 2023, Arya et al. 2024). However, it has no bracts (bracts caducous), a unique character among the members of the group. Further S. bengalensis diplays zygomorphic flowers [as S. mcclintokiae , the other species having actinomorphic flower), ellipsoid gynoecium (as S. mcclintokiae ), and capsules ellipsoid-elongated ( S. mcclintokiae ). The SEM studies of seeds and pollens suggested that the tubercles pointed with less papillae as well as pollen (as in S. mcclintokiae and S. media ). This group is usually characterized by leaves ovate to elliptical or broadly lanceolate, the basal and middle cauline leaves being petiolate; five sepals and five usually bifid petals (the latter sometimes reduced or even absent). So far, the group includes six species namely, Stellaria cupaniana ( Jordan & Fourreau 1868:19) Béguinot (1908: 552), S. mcclintockiae , S. media (L.) Vill., S. neglecta Weihe & Bluff , S. pallida ( Dumortier 1827: 109) Crépin (1866: 19) and S. ruderalis M.Lepší, P.Lepší, Z.Kaplan & P.Koutecký (2019: 405) are known from native to Eurasia and North Africa ( Lepší et al. 2019) and now, this new species stands its identity into this S. media group.

The new species can be distinguished from other species of media group like S. cupaniana with respect to bract (absent vs. present in S. cupaniana ), petal (shorter or included within sepal vs. equaling the length of sepal) seeds (sharp pointed with less papillae vs. conical flat tubercles and gynoecium (ellipsoidal vs. ovoid). Furthermore, from S. neglecta by absence of bract, capsule (double the length of persistent calyx vs. shorter than the length of the persistent calyx) and seed (tubercles sharp pointed with vs. tubercles blunt). It is also differs from S. pallida (Dumort.) Crép. with respect to absence of bract, petal (unimorphic present vs. absent) and capsule shape (ellipsoidal vs. ovoid). Also, from S. ruderalis (2019: 405) by absence of bracts vs. present and seeds (tubercles sharp pointed vs. tubercles conical and wide). The recently described S. mcclintockiae is also easily differentiated by the absence of bract, unimorphic petals, seed morphology and pollen characters.

A Key to the species of Stellaria media aggregate (with S. bengalensis reaching to 7 in number), modified from El Mokni et al. (2023), follows:

1. Petals absent or very short (less than half of the sepal length), seeds ≤ 0.8 mm in diameter, pale yellowish to light brown, stamens 1–3(–5) ................................................................................................................................................................................. S. pallida

1. Petals usually present (longer than half of the sepal length, sometimes equaling the calyx length), seeds> 0.8 mm in diameter, brown to dark-reddish-brown, stamens usually more than 3 (up to 10).............................................................................................2

2. Petals as long or slightly longer than the sepals; stamens (8–)10 ...................................................................................... S. neglecta

2. Petals usually shorter than the sepals; stamens usually 3–5(–10) in S. ruderalis ..............................................................................3

3. Seeds with conical tubercles about 0.14 mm long; flowers usually arranged in dense inflorescences............................. S. ruderalis

3. Seeds with flat-topped or rounded tubercles or conical tubercles less than 0.10 mm long; flowers arranged in lax inflorescences.4

4. Stems pubescent all round; seeds 1.3–1.5 mm in diameter............................................................................................. S. cupaniana

4. Stems with 1(–2) lines of hairs (alternate in successive nodes) or rarely glabrous; seeds 0.8–1.3 mm in diameter..........................5

5. Seeds with usually flat-topped or rounded tubercles; capsule ovoid as long as the persistent calyx..................................... S. media

5. Seed with tubercles pointed and spinulose with less papillae; capsule ellipsoidal exceeding the length of the persistent calyx ......6

6. Bract absent; petal unimorphic; capsule 1/4 the length of persistent calyx .................................................................. S. bengalensis

6. Bract present; petal dimorphic; capsule double the length of persistent calyx ......................................................... S. mcclintockiae

Figures

FIGURE 1. Stellaria bengalensis: a. habit; b. flowering twig; c. flower; d. sepal; e. petal lobe; f. petal; g. stamen; h. gynoecium; i. & j. capsule; k. seed.

FIGURE 2. Stellaria bengalensis: a. flowering twig; b. flower; c. sepal; d. peal lobe; e. petals; f.gynoecium; g. & h. capsule; i. seed.

FIGURE 3. Stellaria media: a. pollen; c. pollen pore; Stellaria bengalensis: b. pollen; d. pollen pore.

FIGURE 4. Stellaria media: a. seed; c. seed surface; e. enlarged surface showing single epidermal pattern; Stellaria bengalensis: b. seed; d. seed surface; f. enlarged surface showing single epidermal pattern.

FIGURE 5. Distribution map of Stellaria bengalensis.