Impatiens rostrata Souvann. & Lanors.

Souvannakhoummane, K., Newman, M. F., Lanorsavanh, S. & Suksathan, P., 2021, Impatiens rostrata (Balsaminaceae), a new species from Khammouane Province, Laos, and nine new records, Edinburgh Journal of Botany 78 (362), pp. 1-15 : 2-5

Impatiens rostrata Souvann. & Lanors. , sp. nov.

Impatiens sect. Semeiocardium (Zoll.) S.X.Yu & Wei Wang , Cladistics 32, 2: 191 (2015). Similar to Impatiens bonii Hook.f. in having connate lateral united petals and 4-carpellate ovary, and in overall flower shape, but differs in having leaf bases cordate to cuneate (not rounded), flower yellow with white lobe apex, red spots inside (not red patch inside with violet lobe apex), lateral sepals 4 (not 2), simple spur (not bifid), dorsal petals oblong-elliptic (not obcordate), seeds ovoid-oblong (not globose).

– Type: Laos, Khammouane Province, Mahaxay District, Natoung village , Phou Hin Poun National Protected Area , humid deciduous forest on limestone, 17°30′23.4′′N 105°10′06.5′′E, 200 m, 21 vii 2019, Lanorsavanh, S., Souvannakhoummane, K. & Xaiyyavong, K. SL 1782 (holotype HNL; isotypes E, FOF, QBG, Biology herbarium, Faculty of Natural Science, National University of Laos). Figures 1 , 2 .

Annual, glabrous herb, up to 50 cm tall. Stems erect, succulent, 20–30 cm long, 0.4–1 cm in diameter, smooth, often becoming decumbent and rooting at the base, branched at top of stem, thin, slender, 3–25(–30) cm tall, with conspicuous leaf scars. Leaves spirally arranged, crowded at top of main stem and alternate at branches; petioles red to green, 0.5–9.5 cm long on lower leaves, 0.5–3 cm long on upper leaves, with a pair of glands adjacent to leaf base; lamina broadly ovate to cordate, 4–9.5(–12) × 3.5–6.5 cm, base cordate to cuneate, margin crenate, apex acuminate, adaxial surface dull green, puberulent, abaxial surface light green, verrucose, secondary veins 10–16 pairs. Inflorescences axillary, solitary or fascicled, below the leaves; pedicels erect to slightly curved, 4–6 mm, puberulent. Bracts conspicuous, ovate-linear, 1–2 × 0.5–1.5 mm, verrucose, persistent. Flowers white with deep yellow to red-brown cross-stripes inside; lateral sepals 4, yellowish green, outer sepal pair ovate-orbicular, 4–6 × 3.5–4 mm, puberulent, apex with a thick blunt mucro, inner sepal pair narrowly linear, 0.4–0.6 mm long; lower sepal navicular, yellow, with reddish spots inside, 2–4 mm deep, 8–10 mm long, outer verrucose, pale green with brown spot, apex with a thick blunt mucro, incurved with a stout spur, 4–5 mm long, apex narrow-beaked; dorsal petal oblong-elliptic, 5–6 mm long, 2.7–3 mm wide, puberulent, crest thick, prominent at centre with mucro near apex, apex emarginate, yellow outside with green crest, yellow inside with red patch; lateral united petals connate, 12–15 × 8–10 mm; upper petals semi-orbiculate, 3–4 × 5–6 mm, yellow with red patch inside; lower petals orbiculate, 7–1 × 10–12 mm, yellowish to white, apex bifid; basal auricles orbiculate, c. 1 mm long; filaments and anthers pale cream to yellow, apex rounded. Ovary ellipsoid, 4-carpellate, pale green, glabrous, axile placentation, ovules numerous, ovoid, white. Capsules clavate, 15–25 mm long, verrucose to puberulent. Seeds 4–12(–15), oblongoid, yellowish-brown, c.2 × 1 mm, rugose.

Distribution. Central Laos, Khammouane Province, Mahaxay District, Phou Hin Poun National Protected Area.

Habitat and ecology. Growing in sandy soil in clefts in rock in deciduous forest, associated with Calanthe cardioglossa Schltr. and Bulbophyllum sp. ( Orchidaceae ), Microchirita sp. ( Gesneriaceae ) and Begonia sp. ( Begoniaceae ).

Phenology. Flowering during the rainy season, from July to September; fruiting late July to October.

Etymology. The epithet is from the Latin, rostratus, meaning ‘beaked’, referring to the beak-shaped spur.

Proposed IUCN category. Least Concern (LC). Impatiens rostrata is currently known only from the type locality within Phou Hin Poun National Protected Area, restricted to a single locality where the population comprises c.30 individuals. Phou Hin Poun National Protected Area measures 1690 km 2, and this can be taken as the extent of occurrence. The area of occupancy is 4 km 2, but this is likely to be an underestimate. Because the whole distribution of Impatiens rostrata is within a National Protected Area, it must be assessed as LC at present. It should be noted, however, that this is a limestone area and mining for cement manufacture may be tolerated, even if it is not strictly legal. For this reason, the locality should be frequently monitored for damage.

The new species belongs to Impatiens sect. Semeiocardium , a large group that includes c.70 species in Southeast Asia ( Yu et al., 2015), all with connate lateral united petals.

Figures

Figure 1. Impatiens rostrata Souvann. & Lanors., sp. nov. A, Plant with flower from above; B, flower, lateral view; C, flower, front view; D, outer lateral sepals; E, inner lateral sepals; F, lower sepal; G, dorsal petal; H, lateral united petals; I, ovary and stamens; J, fruits. Scale bars: A, 5 cm; B–H and J, 1 cm; I, 5 mm. Drawn from Lanorsavanh et al. SL 1782 (A–C, from living plant; D–I, from spirit material) by K. Souvannakhoummane.

Figure 2. A–F, Impatiens rostrata Souvann. & Lanors., sp. nov.: A, plant with flowers; B, flowers at branch apex; C, partial front view of flower; D, lateral view of flower; E, fruit; F, seed. G and H, Impatiens bonii: G, plant with flower; H, front view of flower. Scale bars: A–E, G and H, 1 cm; F, 1 mm. Photographs: A–E, S. Lanorsavanh; F, K. Souvannakhoummane; G and H, T. N. Bon.