Platanthera australis L. Wu, X. L. Yu, H. Z. Tian & J. L. Luo, 2017

Wu, Lei, Luo, Jin-Long, Tian, Huai-Zhen & Yu, Xun-Lin, 2017, Platanthera australis, a new species of Orchidaceae from southern China, Phytotaxa 308 (1), pp. 131-136 : 131-134

Platanthera australis L. Wu, X. L. Yu, H. Z. Tian & J. L. Luo , sp. nov., Figs 1 & 2

Type: — CHINA. Hunan Province: Chenzhou City, Yizhang County, Mangshan National Nature Reserve , elevation ca. 1350 m, 22 June 2016, L. Wu and J. L. Luo 5481 (holotype CSFI!; isotype PE!)

Diagnoses: —This species is similar to P. longicalcarata and P. tipuloides but differs from the former mainly by its much shorter lip and longer spur, and from the latter by its strongly upward-curvedlip.

Description:—Herb, terrestrial, 25 ‒ 45 cm tall. Rootstock fusiform, fleshy, 1.5 ‒ 5 cm long. Stem slender, erect, with 1 ‒ 2 tubular sheaths at the base. Leaves 3 ‒ 5, cauline, scattered, sessile, glabrous, the largest at the base, 6.4 ‒ 9.5 × 2.1 ‒ 2.8 cm, oblong-elliptic to elliptic, apex obtuse to acute; grading into 3 ‒ 4 sterile bracts, 2.2 ‒ 7.7 × 0.4 ‒ 1.4 cm, lanceolate to linear-lanceolate. Inflorescence racemose, 11.5 ‒ 23.5 cm long, laxly 13 ‒ 30-flowered. Floral bracts lanceolate to linear-lanceolate, 4.5 ‒ 17.4 × 1.2 ‒ 5.5 mm, apex acuminate, mostly shorter than ovary. Flowers yellowish-green; pedicel and ovary cylindric, glabrous, 9.5 ‒ 12.8 mm long; dorsal sepal nearly orbicular, 2.5 ‒ 3 mm in diam., 3-veined, margin entire, apex acute or obtuse; lateral sepals reflexed, obliquely elliptic, ca. 3 × 1 mm, apex obtuse; petals obliquely ovate-elliptic, ca. 3 × 1.5 mm, apex obtuse, erect, forming a hood with dorsal sepal; lip ovate-lanceolate, fleshy, 3 ‒ 3.5 × 1.5 ‒ 2 mm, upward-curved, apex connivent with petals; spur slender cylindrical, much longer than pedicel and ovary, 13 ‒ 18mm long, clavate, slightly curved forward; column short, ca. 1.5 mm long; anther locules parallel,connective narrow, ca. 0.5 mm wide; pollinarium ca. 0.6 mm long, with caudicle and viscidium, caudicle ca. 0.4 mm long, slender, viscidium ca. 0.4 × 0.3 mm long, reniform; staminodes ellipsoidal, 0.5 ‒ 0.6 mm long, obvious; rostellum elliptic, developed; stigma forming a concavity under the rostellum.

Distribution and Ecology: —Until now, only three populations of the new species have been found and all are known from Nanling Mountains ( Fig. 3 .), which cross from east to west in southern China. The plants of the new species prefer to grow on humid mountain slopes or along streams in evergreen broad-leaved forest at elevation range of 840 ‒ 1500 m, with the dominant forest including tree species of Fagaceae , Lauraceae , Theaceae , Styracaceae and Magnoliaceae .

Phenology:—Flowering from May to July.

Etymology: —The specific epithet refers to the geographical distribution of the species which grows in southern China.

Conservation status: —Although three populations of the new species were found in Nanling and Mangshan National Nature Reserves, the area of occupancy is estimated to be less than 12 km 2 in total and the population size at each site is less than 40 individuals. All populations are located near hiking trails and thus subjected to disturbances from hikers. According to the IUCN (2016) Red List Categories and Citeria, the status of Platanthera australis is here assessed as Endangered [B2ab (iii,iv,v); D].

Taxonomic notes: — Platanthera australis is similar to P. longicalcarata Hayata (1911: 350) by having a dorsal sepal that forms a hood with the petals and by its upward-curved lip, but it differs in its dorsal sepal which is nearly orbicular and 2.5 ‒ 3 mm in diam. (vs. ovate-triangular and 3 ‒ 3.5 × 2.8 ‒ 3.3 mm), the lateral sepals obliquely elliptic and ca. 3 × 1 mm (vs. ovate-lanceolate and 4.5 ‒ 5.5 × 2 ‒ 3 mm), the lip ovate-lanceolate and 3 ‒ 3.5 × 1.5 ‒ 2 mm (vs. ovate-triangular and 4.5 ‒ 5 × 1.8 ‒ 2.5 mm), and the spur 13 ‒ 18 mm long (vs. 6 ‒ 8 mm long). A further difference is the flowering period from May to July (vs. July to September). It also resembles P. tipuloides (Linnaeus f. 1781: 401) Lindley (1835: 295) by having a similar habit, but differs by its leaves 6.4 ‒ 9.5 × 2.1 ‒ 2.8 cm (vs. 5 ‒ 11 × 0.8 ‒ 2 cm), the petals obliquely ovate-elliptic and ca. 3 × 1.5 mm (vs. ovate to narrowly ovate, oblique and 2.5 ‒ 3 × 1 ‒ 1.5 mm), and the lip ovate-lanceolate, curved upwards and 3 ‒ 3.5 × 1.5 ‒ 2 mm with the apex long acuminate and connivent with the petals (vs. spreading horizontally to pendulous, broadly linear and 5 ‒ 6 × 1.2 ‒ 1.5 mm).

Figures

FIGURE 1. Platanthera australis. A: Habit. B: Flower (front view). C: Flower (side view). D: Ovary, column and lip (side view). E: Sepals, petals and lip. F: Column. (Drawn by Jing Tian after the holotype).

FIGURE 2. Platanthera australis.A: Habit. B: Inflorescence. C: Flower in face view. D: Flower in side view. E: Flower in back view. F: Column. (scale: B 1 cm; C & D 5 mm; E 3 mm; F 1 mm.)

FIGURE 3. Geographical distribution of Platanthera australis.