Argostemma tortilobum K.Y.Fang, K.S.Nguyen & Y.H.Tong, 2022

Fang, Ke-Yi, Tong, Yi-Hua, Vu, Tien-Chin, Nguyen, Khang-Sinh & Xia, Nian-He, 2022, Argostemma tortilobum (Rubiaceae), a new species from Vietnam, Phytotaxa 567 (1), pp. 105-109 : 106-107

Argostemma tortilobum K.Y.Fang, K.S.Nguyen & Y.H.Tong , sp. nov. ( Figs. 1 , 2 ).

Similar to A. sarmentosum in having opposite and anisophyllous leaves, 4-merous flowers, deeply lobed calyx and free yellow anthers, but differs in having erect (vs. creeping at the base) stem without runners (vs. with long filiform runners), densely pilose (vs. glabrous) peduncle and twisted (vs. flat) corolla lobes with ciliate (vs. glabrous) margins. A more detailed comparison between the two species is provided in Table 1 .

Type:— VIETNAM. Ha Giang Province: Yen Minh District, Du Gia Nature Reserve , N 22°42’53’’, E 105°11’46’’, 244 m a.s.l., 24 May 2018, N.H. Xia, J.B. Ni, Y.H. Tong, Y.Y. Zhang & V.D. Nguyen TYH-1565 (holotype IBSC0886643, isotypes IBSC0886642, VNMN) .

Herb, perennial. Roots fibrous. Raphides linear, less than 0.5 mm long, present throughout the plant, especially on the abaxial surface of foliaceous scales, stipules, leaf blades, bracts and calyx and corolla lobes. Stem 1 to several borne from a sub-globose tuber, erect, unbranched, 2.3‒9.1 cm long, with stipules, petioles, leaf blades, peduncles, pedicels and calyx more or less white-pilose, trichomes multicellular, with one or two pairs of opposite foliaceous scales inserted at 1.3‒6 cm from the base, scales ovate, 1.5‒5 × 1‒3.5 mm, margin ciliate. Stipules large, leaf-like, lanceolate to ovate, 6‒11 × 2‒7 mm, acuminate at apex, margin ciliate. Petiole short, 0.2‒0.7 mm long. Leaves opposite, in one pair, anisophyllous, green adaxially, usually with white veins; blades thinly papery to membranaceous in sicco, broadly lanceolate, ovate to suborbicular, larger ones 4.5‒10.2 × 2.2‒7.7 cm, smaller ones 2.3‒5.3 × 1.7‒4.2 cm, acute, attenuate to acuminate at apex, asymmetrical or oblique at base, sometimes truncate, margin slightly undulate and densely ciliate; midvein distinct, with secondary veins slightly impressed adaxially and slightly raised abaxially, secondary veins 5‒9pairs, brochidodromous and reticulate.Inflorescence scorpioid-cymose, with 3‒8 flowers, terminal, unbranched or sometimes with a smaller branch at base; peduncle 1.8‒3.6 cm long; pedicel 2.5‒10 mm long; bracts 4, broadly lanceolate, bright green, 1.5‒2 × 1.1‒1.5 mm, margin ciliate; calyx deeply 4-lobed, lobes ovate, white, 2‒4 × 1‒2 mm, persistent, margin ciliate, with conspicuous veins; corolla with 4 pilose edges (sutures of lobes) when in buds, star-shaped when opened, tube very short, 1‒2 mm long, green, lobes 4, oblong-lanceolate, white, twisted, 5‒8.2 × 1.2‒1.8 mm, glabrous on both surfaces, margin ciliate, with conspicuous veins; stamens 4, inserted at the base of corolla tube; filaments free, less than 1 mm long, white, glabrous; anthers free, slightly furcate at the base, narrowed upwards, bright yellow, 4‒5 mm long, appressed to style, opened by apical pores; style glabrous, equal to or slightly longer than stamen, 4.5‒5.5 mm long, white; stigma globose, ca. 0.1 mm in diam.; ovary inferior, hemispherical, 1.5‒2 mm in diam. Fruit and seed unknown.

Distribution and ecology: — Argostemma tortilobum is only known from the type locality in Ha Giang. It grows on wet limestone rocks covered by dense mosses.

Phenology: —Flowering in May.

Etymology: —The specific epithet refers to the twisted corolla lobes of this new species.

Conservation status: —We only found two small populations with ca. 100 individuals of Argostemma tortilobum in Du Gia Nature Reserve. Due to limited time, population assessment of this species in the field was not made. Thus, it is best assigned a status of ‘Data Deficient’ (DD) at present ( IUCN Standards and Petitions Committee 2022).

Additional specimens examined: — Argostemma tortilobum (paratype): Vietnam: Ha Giang Province: Yen Minh District, Du Gia Nature Reserve, on limestone mountain along Gam River , N 22°41’52’’, E 105°13’26’’, 209 m a.s.l., 22 May 2018, N.H. Xia, J.B. Ni, Y.H. Tong, Y.Y. Zhang & V.D. Nguyen TYH-1543 (IBSC0886641) .

Argostemma sarmentosum : Nepal: Gosain Than, without date, B. Singh 8396.B (syntypes: K000030999 (photo), K000031002 (photo), K000031003 (photo), K001125386 (photo); isosyntypes: BM000945061 (photo), L0043125 (photo)); Morang, 29 July 1820, without collector 8396.D (syntype, K001125730 (photo)) . India: Kumaon, without date, R. Blinkworth 8396.C (syntypes, K000030998 (photo), K000031001 (photo), K001125387 (photo), isosyntypes E00438132 (photo), BM000945062 (photo), S14-36657 (photo)) .

Figures

FIGURE 1. Argostemma tortilobum. A. Habitat and habit; B. Flowering plants with white veins on leaf blades; C. A flowering plant with green veins on leaf blades and an inflorescence with a small branch at the base; D. Distal part of an inflorescence, showing young flowers with four pilose edges (sutures of corolla lobes) and one opened-flower with marginally ciliate calyx, star-shaped corolla, twisted corolla lobes and four free yellow anthers. Photographed by Yi-Hua Tong.

FIGURE 2. Argostemma tortilobum. A. Habit, arrow showing the detail of the adaxial (up) and abaxial surface of leaf blade; B. Flower; C. pedicel and calyx; D. Calyx lobe; E. Corolla lobe; F. Anthers, ventral (left) and dorsal (right) view; G. Style and stigma. Scale bars: A 2 cm, B 5 mm, C, D, E, F and G 2 mm. Drawn by Mr. Ding-Han Cui.