Impatiens tanintharyiensis Ruchisansakun, Suksathan & Saw-Lwin, 2017

Ruchisansakun, Saroj, Suksathan, Piyakaset, Niet, Timotheüs Van Der & Janssens, Steven B., 2017, Impatiens tanintharyiensis (Balsaminaceae), a new species from Southern Myanmar, Phytotaxa 296 (2), pp. 171-179 : 172-177

Impatiens tanintharyiensis Ruchisansakun, Suksathan & Saw-Lwin , sp. nov. ( Figs. 1 , 2 )

Impatiens tanintharyiensis Ruchisansakun, Suksathan & Saw-Lwin is morphologically similar to I. spectabilis Triboun & Suksathan but can be distinguished by having asymmetric flowers due to anticlockwise distorted lateral united petals, a saccate-bucciniform lower sepal, and a shorter, slightly incurved spur.

Type: — MYANMAR. Tanintharyi Region: Dawei, Thet Kal Kwet Village, Hawang falls, ca. 146 m elevation, 17 August 2015, Ruchisansakun & Thet Yu Nwe 707 (holotype L!, isotypes L!, RAF!, RANG!).

Terrestrial to lithophytic, annual, glabrous herb, 15–25 cm high. Stems erect, cylindrical with small ridges near the nodes, 3–7 mm in diam., simple to sparsely branched, upper part slightly zig-zagged, purplish red with dark purple dots. Leaves spirally arranged; petioles 10–30 mm long, 1–1.5 mm in diam., green to red with dark red dots; laminas 40–65 mm × 15–25 mm, elliptic to ovate to lanceolate, apex acute, base obtuse to attenuate, margin shallowly serrate, adaxial green, abaxial pale green; lateral veins 4–5 on each side of midrib; extra-floral nectaries present as a stalked short glands on each side of the base of the leaf margin. Flowers axillary, solitary, highly asymmetric due to anticlockwise distorted lateral united petals, 35–40 mm, purplish pink, centre white with two yellow marks. Bracts minute, ca. 2 × 1 mm, narrowly triangular, apex acute, base cuneate, green. Pedicels slender, 20–30 mm long, ca. 1 mm in diam., the same colour as stems. Sepals 3. Lateral sepals 2, 5–7 × 5–6 mm, ovate to broadly ovate, sometimes slightly oblique, apex acute to acuminate and mucronate, base obtuse to cordate, purplish pink with green tips. Lower sepal 13–16 mm long, 8–10 mm wide, 14–15 mm deep, saccate-bucciniform, purplish pink outside, whitish inside with dark pink veins and yellow marks at the throat, distal part gradually constricted into a long, slightly incurved spur, 19–22 mm long, pink with dark pink dots. Petals 5. Dorsal petal strongly reflexed, 12–13 × 15–17 mm, broadly ovate to broadly elliptic to broadly obovate, purplish pink with a green tip, apex cordate and mucronate, base cuneate with a basal triangular crest. Lateral united petals connate, asymmetric due to distorted lateral united petals; upper petals 12–15 × 18–22 mm, broadly depressed obovate, apex round to truncate, purplish pink with white base; lower petals connate, 23–30 × 9–13 mm, obovate in outline, anticlockwise distorted, apex round to shallowly bilobed, purplish pink, the base white with a yellow mark. Stamens 5; filaments ca. 4 mm long, flat, white; anthers white. Ovary ca. 4 mm long, 1 mm in diam., 4- carpellate, green, glabrous. Fruits loculicidal dehiscent capsules, 4-lobed, 15–17 mm long, ca. 3 mm in diam., clavate. Seeds ca. 2.5 mm long, 14–16 per capsule, brown.

Phenology:— Flowering period August–September.

Distribution:— Endemic to Southern Myanmar (Tanintharyi Region), only known from two localities.

Ecology:— Growing among decaying organic material on low granular metamorphic rock of granitic schist facies (Phongphat Prasong, pers. comm), along a waterfall at 146–155 m above sea level.

Common name:— Tanintharyi Dan Pan, Tanintharyi balsam.

Proposed IUCN conservation assessment:— Endangered (ENB2 ab(iii,v)) based on a preliminary risk of extinction assessment using the IUCN red list categories and criteria ( IUCN 2012). This species is only known from 2 localities, 2 km apart on the same mountain range. The Hawang Falls locality is under severe pressure from local tourism. Since there are fewer than 100 individuals at each locality, it is assumed that human activities in the region could lead them to rapid extinction ( IUCN 2012).

Etymology:— The specific epithet refers to its locality, the Tanintharyi region of Myanmar.

Additional specimens examined (paratypes):— MYANMAR. Tanintharyi division: Dawei, Thet Kal Kwet Village, Rachaung falls, 155 m above sea level, growing on rocks in a shady area along a waterfall, 17 August 2015, Ruchisansakun & Thet Yu Nwe 708 (L, RAF, RANG).

Note:— Based on the presence of connate lateral united petals and a 4-locular ovary, Impatiens tanintharyiensis is a member of Impatiens sect. Semeiocardium (Zoll.) S.X. Yu & Wei Wang (2015: 13) ( Ruchisansakun et al. 2015, Yu et al. 2015). The species can be distinguished from closely related species due to the presence of asymmetric flowers (caused by distorted lateral united petals), a saccate-bucciniform lower sepal, and a slightly incurved long spur. An additional comparison to its closest relatives is shown in Table 1.

Phylogenetic analysis:— Bayesian phylogenetic analyses of the ITS and atpB-rbcL datasets also recovered I. tanintharyiensis as part of Impatiens sect. Semeiocardium ( Fig. 3 ), although some incongruence between the nuclear and plastid topologies was observed (cf. Janssens et al. 2006, Ruchisansakun et al. 2015). According to the majority rule consensus tree based on analysis of ITS sequences, the new species is strongly supported (Bayesian Posterior Probability (BPP): 1.0) as part of a clade in which it is sister to a clade containing I. spectabilis Triboun & Suksathan , I. larsenii T. Shimizu (1977: 33) , I. siamensis T. Shimizu (1977: 34) , I. suksathanii Ruchisansakun & Triboun (2014: 237) , I. nalampoonii T. Shimizu (1969: 39) , I. ruthiae Suksathan & Triboun (2009: 172) , I. daraneenae Suksathan & Triboun (2009: 164) , I. namkatensis T. Shimizu (2000: 37) , and I. psittacina Hook.f. (1901: 7809) ( Fig. 3 ). In contrast, the majority rule consensus tree of the plastid sequences shows that I. tanintharyiensis is part of relatively weakly supported polytomy (BPP: 0.83) consisting of I. suksathanii , a clade containing I. siamensis and I. nalampoonii , and a clade containing I. larsenii , I. ruthiae , I. daraneenae , I. namkatensis and I. psittacina , but without I. spectabilis ( Fig. 3 ). Topological incongruence between two gene trees, in particular those based on plastid versus nuclear loci, may be the result of ancient hybridization ( Alvarez & Wendel 2003, Wang et al. 2016); yet, more data is required to understand the exact evolutionary history of the new species.

Pollination ecology:— A recent comparative study of floral morphology and pollination ecology demonstrated that the closely related and morphologically similar I. daraneenae , is pollinated by bees ( Ruchisansakun et al. 2016). The presence of a large floral chamber with a wide entrance are traits associated with bee pollination in Southeast Asian Impatiens ( Ruchisansakun et al. 2016) . Based on the traits of the new species, we hypothesize that the new species is also bee-pollinated.

Figures

FIGURE 1. Impatiens tanintharyiensis. A. Lateral view of flower; B. Front view of flower; C. Habit in situ. Photographs by Saroj Ruchisansakun.

FIGURE 2. Impatiens tanintharyiensis. A. Habit; B. Fruit; C. Front view of flower; D. Lateral view of flower; E. Outer lateral sepals; F. Lower sepal; G. Dorsal petal; H. Lateral united petals. Drawn by Saroj Ruchisansakun.

FIGURE 3. Majority rule consensus trees from Bayesian analyses of nuclear ITS (left) and plastid atpB-rbcL (right) DNA sequences. Impatiens tanintharyiensis is highlighted in bold font and with an asterisk. Bayesian posterior probabilities are indicated at each node.