Impatiens darachuensis P.Gyeltshen, W.Adamowski & Phuntsho, 2023

Gyeltshen, Phub, Adamowski, Wojciech, Phuntsho, Tashi & Thinley, Kinga, 2023, IMPATIENS DARACHUENSIS (BALSAMINACEAE), A NEW SPECIES FROM BHUTAN HIMALAYA, Edinburgh Journal of Botany 80 (1939), pp. 1-12 : 2-8

publication ID	https://doi.org/ 10.24823/EJB.2023.1939
persistent identifier	https://treatment.plazi.org/id/724C6505-E72E-FFA4-7978-FC83C7CAFB3E
treatment provided by	Felipe
scientific name	Impatiens darachuensis P.Gyeltshen, W.Adamowski & Phuntsho
status	sp. nov.

Treatment

Impatiens darachuensis P.Gyeltshen, W.Adamowski & Phuntsho View in CoL , sp. nov.

Impatiens darachuensis is most similar to I. duclouxii and I. cathcartii in having scorpioid cyme, but it is distinguished from I. duclouxii by its larger habit, longer peduncle

(30–50 mm vs 25 mm), 3–9 flowers per inflorescence (vs 3–6), crenate leaf margins (vs coarsely serrate), longer capsule (30–36 mm vs 15–25 mm), 4 lateral sepals (vs 2 lateral sepals), and inner lateral sepals oblong (vs absent) with a prominent crest on the basal part. It differs from Impatiens cathcartii in its hairy leaf surface especially on veins (vs glabrous), 4 lateral sepals (vs 2), shorter peduncle (30–50 mm vs 40–60(–100) mm), and subfusiform capsule (vs cylindrical). It is also similar to Impatiens jurpia and I. discolor in having a bucciniform lower sepal but differs from those species by its subscorpioid cyme, 4 lateral sepals, subfusiform capsule, and oblong inner lateral sepals. – Type: Bhutan, Sarpang, Darachu area, 1700–1950 m elevation, 20 ii 2020, P. Gyeltshen 35 (holotype THIM!, isotype THIM!). Figures 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 .

Terrestrial, erect perennial herbs, 30–200 cm tall. Roots densely puberulent, pale green to pale greenish white. Underground stems pale green, glabrous, nodes swollen. Aerial stems single, branched at base to halfway up the stem, terete, woody at base, not winged, green, pale green or pale purplish at distal portions, glabrous, nodes swollen. Leaves alternate, laxly arranged on the upper half of the stem; petioles slender, 1.5–7 cm long, sometimes with a pair of glands just below the lamina, pale green, glabrous; lamina ovate-lanceolate to ovate-elliptic, 8–19 × 3.5–7.5 cm, base oblique, obtuse or rounded, apex acuminate or caudate-acuminate, margin crenate with thick setae, abaxially pale green, glabrous with sparse hairs on midrib and lateral veins, adaxially dark green sparsely hairy, midvein and lateral veins prominent ventrally, dorsally depressed, with 8–10 veins on each side of the midvein. Inflorescence subscorpioid cyme, terminal or axillary, 3- to 9-flowered; peduncle 3–5 cm long, green, glabrous, with 2–5 surperfluous bracts below the lowest flower;

bracts flat, deltoid, 2.5–4 × 3.5–4 mm, glabrous, green, margins entire, apex mucronate, swollen. Flowers 4–4.2 cm deep, 5.4–5.6 cm long, yellow or creamy, bud tinged with reddish striations; pedicel 10–23 mm long, green, glabrous. Lateral sepals 4, outer lateral sepals obliquely suborbicular, 10–11 × 9–10 mm, apex swollen mucronate, margin entire, semitransparent, pale greenish white, glabrous, midrib at extreme inner position, prominent, thick; inner lateral sepals minute, oblong, with prominent crest in basal part, pale greenish yellow, glabrous, 1.8–2 × 0.8–1 mm, apex rounded. Lower sepal bucciniform, 22–25 mm long, tube 12–15 mm wide (excluding spur), abruptly constricted into short deep incurved spur, yellow with or without red nerves inside, spur deeply incurved at apex, 13–17 mm

long, apex obtuse, pale yellow, glabrous. Dorsal petal slightly cucullate, suborbicular,

12–15 × 15–16 mm when flattened, base rounded, apex retuse, margins entire, yellow with reddish nerves ventrally, glabrous horn-like keel on adaxial side, 12–13 mm long, apex acute. Lateral united petals 30–36 mm long, 2-lobed; basal lobe obovate or suborbicular, 17–18 × 17–18 mm, apex emarginate to obtuse, yellow with reddish streaks, glabrous;

distal lobe dolabriform, 19–21 × 9–10 mm, apex obtuse to abruptly lobed, yellow with reddish nerves; dorsal auricle triangular, 3.5 × 3 mm, apex broadly acute, yellow. Androecium c.5–10 × 2.5–3 mm, curved towards the apex, stamens 5, connate, surrounding the gynoecium, filaments c. 5–10 mm long, narrow at the base and broader at the apex, free in the middle, anthers c. 3.8–5 mm long, apex cuspidate, white. Pistil c. 1 cm long. Capsule long, subfusiform, 30–36 × 4.5–5 mm, slightly curved, green, glabrous, seeds numerous, spherical, c.2 × 1.5 mm, surface warted, brown.

Distribution. Darachu, Sarpang district, Bhutan (known only from the type locality).

Habitat and ecology. Impatiens darachuensis grows in semi-moist areas along the roadside at elevations ranging from 1700 to 1920 m in the warm broadleaved forest. Flowering and fruiting from October to November. The associated species are Aster verticillatus (Reinw.) Brouillet, Semple & Y.L.Chen , Begonia annulata K.Koch , Craniotome furcate (Link) Kuntze , Diplazium javanicum Makino , Girardinia diversifolia (Link) Friis , Gonostegia triandra (Blume) Miq. , Hydrangea febrifuga (Lour.) Y.De Smet & C.Granados , Hydrocotyle himalaica P.K.Mukh. , Impatiens stenantha Hook.f. , Koenigia mollis (D.Don) T.M.Schust. & Reveal , Lobelia montana Reinw. ex Blume , Melissa axillaris (Benth.) Bakh.f. , Persicaria chinensis (L.) H.Gross, Ranunculus cantoniensis DC. , Rubus acuminatus Sm. , Rubus paniculatus Sm. , Strobilanthes helicta T.Anderson , Carex sp. , Dennstaedtia sp. , Elatostema spp. Microlepia sp. and Pilea spp. (see Figure 1 A View Figure 1 ).

Etymology. The specific epithet, darachuensis , refers the type locality in Darachu forest, Sarpang.

Proposed IUCN conservation category. Impatiens darachuensis is known only from Darachu in the Sarpang district of Bhutan. We observed fewer than 60 mature individuals at two locations, and the area of occupancy is approximately less than 10 km 2. It is expected that this species may occur in intermediate areas, but so far, no more populations have been observed. The species is under serious threat of extinction due to road maintenance and clearing of plants within the road buffers. The widening of the roads in the near future may lead to loss of its natural habitat. Following IUCN guidelines ( IUCN Standards and Petitions Committee, 2022), we assess Impatiens darachuensis as Endangered [EN B2ab(iii,iv,v); C2a(i); D].

Notes. The key morphological differences between the new species, Impatiens darachuensis , and I. cathcartii , I. discolor , I. duclouxii and I. jurpia are summarised in the Table. The terminology followed in the species description follows Ruchisansakun et al. (2018).

Based on the results of molecular and morphological analyses of the genus, Yu et al. (2015) recognised a subclade ‘F’ (sect. Scorpioidae) characterised by subscorpioid cymes, concave bracts, long and bent (sub)fusiform capsules, and a minutely warted seed coat ornamentation. Impatiens darachuensis shares the majority of these features ( Figures 1 F View Figure 1 , 2 Q View Figure 2 ; Table). The other known species in sect. Scorpioidae are Impatiens conchibracteata Y.L.Chen & Y.Q.Lu , I. duclouxii , I. hunanensis Y.L.Chen and I. rubro-striata Hook.f. , which occur further to the east in Northeast India, Myanmar, southern China and Thailand ( Chen et al., 2007; Gogoi et al., 2018; Ruchisansakun et al., 2018).

Impatiens cathcartii View in CoL is similar to I. darachuensis View in CoL in being a glabrous plant, but it has a much thinner, not involute spur, as well as a short and obtuse crest on the dorsal petal (Gogoi & Sherpa, 2020; Gogoi et al., 2021). In the original description ( Hooker, 1875), the inflorescence is given as a raceme; however, the images in Gogoi & Sherpa (2020, figure 1E) and Gogoi et al. (2021, p. 85–87) clearly show a subscorpioid inflorescence. In Gogoi et al. (2022, p. 86), a subfusiform capsule is also shown for this species.

The recently described species Impatiens bakthangensis (Gogoi et al., 2020) View in CoL shares a subfusiform capsule with I. darachuensis View in CoL and other members of sect. Scorpioidae sensu

Yu et al. (2015) but has, however, a racemose inflorescence. Impatiens cyclosepala Hook.f. ex W.W.Sm. has similar shape of lower sepal and spur as I. darachuensis but differs by its inflorescence subscorpioid cyme, four lateral sepals, and outer sepals obliquely suborbicular with prominent thick green midrib at the inner position. Impatiens bakthangensis is also similar to I. laevigata and I. pseudolaevigata ( Gogoi et al., 2013, 2017) in having four lateral sepals but differs by its larger habit, much longer peduncle, inner lateral oblong sepals with a prominent crest in the basal part, and larger size subfusiform capsule.

Impatiens jurpia View in CoL has a long and pointed appendage on the dorsal petal that is similar to that of the new species ( Grey-Wilson, 1989, 1991; Akiyama & Ohba, 2015; Gogoi et al., 2018), but it has a racemose inflorescence ( Figure 4 View Figure 4 ) and is described as pubescent and has a curved, not involute, spur.

A more detailed study of the inflorescence types, seed-coat micromorphology, and molecular genetics of the species mentioned above is clearly required to reveal their relationship with other species from sect. Scorpioidae.

Additional specimen examined. BHUTAN. Sarpang district : Darachu area, 1700–1920 m, 20 xi 2020, P. Gyeltshen & T. Phuntsho 36 ( THIM) .