Leptomischus multiflorus Nuraliev, K.S.Nguyen & L.Wu, 2022

Nuraliev, Maxim S., Nguyen, Khang Sinh, Pham, Thoa Kim Thi, Nguyen, Cuong Huu, Quang, Bui Hong, Lyskov, Dmitry F., Kuznetsov, Andrey N., Kuznetsova, Svetlana P. & Wu, Lei, 2022, Leptomischus multiflorus (Argostemmateae: Rubiaceae), a new species from southern Vietnam, Phytotaxa 574 (1), pp. 83-90 : 84-88

Leptomischus multiflorus Nuraliev, K.S.Nguyen & L.Wu , sp. nov. ( Figs. 1–3 )

Diagnosis: —The new species differs from all its congeners by the following combination of morphological features: leaf blades up to 23 cm long with up to 25 pairs of secondary veins, many-flowered inflorescences (with up to 32 flowers), and corolla tube less than 10 mm long and hairy outside. It is morphologically closest to L. anisophyllus T.P.Anh, B.H. Quang, Nuraliev & L.Wu in Tran et al. (2021a: 199), differing in weakly anisophyllous (to nearly isophyllous) leaves, many-flowered inflorescences, shorter calyx lobes (ca. 2–2.5 mm long, about 1/3 length of corolla tube), shorter corolla tube (ca. 7–8 mm long), presence of horn-like corolla appendages, shorter anthers (ca. 1–1.3 mm long), style hairy in distal half, pin flowers with filaments adnate at middle of corolla tube and with shorter stigma lobes (ca. 1 mm long), and thrum flowers with shorter style (ca. 2.5–3 mm long).

Contrasting features for L. anisophyllus are listed in Table 1 .

Type: — VIETNAM. Quang Nam Province: Tay Giang District , A Xan Municipality, Lang Po Mu homestay area, forest, in ravine near small stream, 15°49’03’’N 107°19’24’’E, elev. 1450 m, 20 March 2022, Nuraliev M. S., Lyskov D. F. NUR 3486 (holotype: MW: MW0595776 ; isotypes: MW: MW0595777 , MW0595778 ) .

Additional specimens examined (paratypes): — VIETNAM. Quang Nam Province: Tay Giang District , A Xan Municipality, Lang Po Mu homestay area, primary evergreen mixed forest with Fokienia hodginsii , common along stream bank, around point 15°48’18’’N 107°19’52’’E, elev. 1300 m, 19 April 2022, Pham T. K. T., Nguyen C. H., Nguyen K. S., Cao H.X. CKH 2022041911 ( HN; VNF); same location, around point 15°48’58’’N 107°19’46’’E, elev. 1275 m, 20 April 2022, Pham T. K. T., Nguyen C. H., Nguyen K. S., Cao H.X. CKH 2022042072 ( HN; VNF) .

Etymology: —The specific epithet “ multiflorus ” means “many-flowered” and refers to the large number of flowers per inflorescence which distinguishes the new species from most of its congeners.

Description:—Herb perennial, terrestrial, ca. 10–30 cm high, with plagiotropic hypogeous rhizome; plant almost entirely covered with white spreading hairs. Raphides present (visible in corolla). Stem seldom branched, terete, densely covered with hairs ca. 0.5–1 mm long, green; internodes (0.5–) 1–5 cm long, but sometimes much shorter towards apex, up to 4 (rarely to 7) mm in diameter. Stipules interpetiolar, persistent, narrowly to broadly ovate, (8–) 10–19 mm long, ca. 2–6(–12) mm wide, densely hairy on both sides, adaxially dark green and abaxially pale green, with entire to slightly erose margins, acute at apex, with several parallel veins. Leaves opposite, weakly anisophyllous to nearly isophyllous with larger leaf of a pair usually 1.2–2.3(–4) times longer than smaller leaf; petiole stout, from nearly absent to 1.7 cm long, densely hairy; blade oblanceolate to obovate, sometimes slightly falcate, (4–) 6–23 cm long (blades longer than 15 cm usually present on each shoot), (1.0–)2.0– 7.3 cm wide, 2.4–3.7(–4.3) times as long as wide, with entire margins, acuminate to attenuate at apex, cuneate at base, chartaceous in sicco, densely hairy on both sides especially along veins, dark green adaxially and pale green (whitish) abaxially; midvein more or less flat adaxially and strongly raised abaxially; secondary veins 9–25 pairs, alternate or subopposite, slender, nearly flat adaxially and raised abaxially. Inflorescence terminal (rarely with additional axillary inflorescences), cymose, with up to 32 (or probably more) flowers. Peduncle ca. 3–15 mm long, densely hairy similar to stem, greenish white; axes of higher orders densely hairy, white; primary branches up to ca. 20 mm long. Two basal bracts of inflorescence leaf-like, narrowly ovate to lanceolate, up to 20 mm long, up to 4 mm wide, with entire margins, acuminate at apex, densely hairy on both sides, green adaxially, pale green abaxially. Stipules between basal bracts similar to them but broadly ovate and sometimes apically deeply 2-lobed, up to 10 mm long, up to 6 mm wide. Flower-subtending bracts narrowly triangular, ca. 1–1.5(–2.5) mm long, ca. 0.2 mm wide, more or less glabrous adaxially, densely hairy abaxially, white and sometimes with greenish apex, without stipules. Other bracts of intermediate morphology between basal bracts and flower-subtending bracts (gradually becoming smaller and whiter towards higher orders of branching). Flowers actinomorphic, 5(or 6)-merous (except for gynoecium), distylous. Pedicel ca. 1–4 mm long, densely hairy, white. Calyx campanulate, externally (abaxially) densely hairy, internally (adaxially) glabrous, white; tube vanishingly short; calyx lobes narrowly triangular, ca. 2–2.5 mm long, 0.5–1.3 mm wide at base, acuminate at apex, hairy along margin. Corolla tubular (sometimes narrowly funnel-shaped, especially at apex) with rotate limb, indistinctly clavate in bud, ca. 8–9 mm long when fully open, white, turning pale yellow with age, with slightly darker veins on limb; tube ca. 7–8 mm long, 1.5–2 mm in diameter (when flattened) in the middle, outside with dense very short hairs, inside glabrous in proximal 1/3 and with dense long interlacing hairs in distal 2/3 (at throat hairs confined to petal midveins); corolla lobes lanceolate to oblong, more or less curved backwards, ca. 2–4 mm long, ca. 0.5–1.5 mm wide, acute at apex, externally (abaxially) hairy, internally (adaxially) glabrous; each lobe abaxially with prominent horn-like appendage ca. 0.5 mm long (hence flower bud star-shaped at top). Stamens glabrous; filaments filiform, white; anthers dorsifixed, 2-locular, narrowly oblong, ca. 1.0– 1.3 mm long, ca. 0.2–0.4 mm wide, pale brownish. Ovary inferior, cup-shaped, ca. 0.5 mm long, ca. 0.8 mm in diameter, outside densely hairy, white to greenish white, 2-locular; disk concave, ca. 0.3 mm high, very minutely puberulent (visible with magnification), white; placentas axile, attached approximately at middle of ovary septum, bearing numerous ovules; style filiform, white, glabrous in proximal half and hairy in distal half; stigma densely papillate to apparently hairy, white. Pin (long-styled) flowers: filaments adnate at middle of corolla tube, vanishingly short (anthers nearly sessile); anthers deeply included in corolla tube (placed at level of ca. 2/3 of tube); style ca. 7 mm long; stigma 2-lobed, ca. 1 mm long, slightly to evidently exserted from corolla tube. Thrum (short-styled) flowers: filaments adnate at level of 2/3 of corolla tube, ca. 1.5–2(–2.5) mm long; anthers occupying level of corolla throat; style ca. 2.5–3 mm long; stigma tortuous, entire, flat with a central furrow (rarely shortly 2-lobed with lobes tightly appressed to each other), ca. 0.5 mm long, deeply included in corolla tube (placed at middle of tube). Fruit and seeds unknown.

Phenology: —Flowering from March to April.

In March, the species was observed to mainly have postanthetic inflorescences, with corollas largely abscised. Nevertheless, individuals with flowers and flower buds were found a month later in April.

Distribution and ecology: — Leptomischus multiflorus is currently only known from a single forest area in Tay Giang District (Quang Nam Province, Vietnam). The area is locally famous since it is covered by a pristine primary mixed forest with a dense population of the conifer Fokienia hodginsii that is mainly found on ridges and slopes. The known population of L. multiflorus is located about 6 km from the Vietnam-Laos border, not far from Xe Xap National Bio-Diversity Conservation Area in Laos, where the species can potentially also occur.

The new species is common within this forest, inhabiting wet shady banks of small streams at elevations of 1250–1450 m a.s.l.

Taxonomic relationships: —The generic placement of the newly described species is not straightforward due to the general uncertainty of delimitation between Leptomischus and Mouretia , which has been pointed out by Chen et al. (2011) and Tran et al. (2021b). Mouretia is also a member of the tribe Argostemmateae ( Razafimandimbison & Rydin 2019) . In the key provided by Chen et al. (2011), Leptomischus and Mouretia are distinguished solely by the structure of placentas (stipitate, arranged near base of septum vs. peltate, arranged near middle of septum, respectively). With respect to placentation, the species described here seems to fit Mouretia better. However, the characters of placentas appear to be hardly reliable (see also Wu et al. 2020): they are difficult to assess in the herbarium material due to the small size of ovaries in this lineage and poor quality of preservation of ovary structure. In fact, these characters have never been evaluated for many species of the genera in question. At the same time, Leptomischus and Mouretia differ significantly in flower size: for example, the corolla tube in all species of Leptomischus known to date is 6 mm long or longer (often drastically so), whereas in Mouretia it is 2.5–5 mm long ( Tange 1997, Tran et al. 2021b). Based on the flower size, and also on the general similarity of the new species with known species of Leptomischus (especially with L. anisophyllus ), we assign the new species to this genus. Preliminary molecular phylogenetic studies (Lei Wu, unpublished) demonstrated that Leptomischus in its current circumscription is not monophyletic, which possibly indicates the need for redefinition of the limits of genera within Argostemmateae .

Leptomischus multiflorus is readily distinguishable from all the other species of Leptomischus (as summarized by Chen et al. 2011, Hareesh et al. 2017, Wu et al. 2020, Tran et al. 2021a) by the following combination of characteristics: leaf blades up to 23 cm long with up to 25 pairs of secondary veins, and corolla tube less than 10 mm long and hairy outside. In addition, L. multiflorus is remarkable for its many-flowered inflorescences, whereas several-flowered inflorescences are most common in the genus.

The new species is most similar to L. anisophyllus described recently from Pu Mat National Park in northern Vietnam. The main morphological differences between L. multiflorus and L. anisophyllus are summarized in Table 1 . The more important of them are leaf dimorphism (weak vs. strong anisophylly), number of flowers per inflorescence (up to 32 vs. 6–10), absolute and relative length of calyx lobes (2–2.5 mm, about 1/3 length of corolla tube vs. 6–8 mm, more than 1/2 length of corolla tube), length of corolla tube (7–8 mm vs. 10–15 mm), presence of corolla appendages (appendage horn-like, 0.5 mm long vs. absent), anther length (1–1.3 mm vs. 2–2.5 mm), style indumentum (hairy in distal half vs. entirely glabrous), structure of pin flowers (filaments adnate at middle of corolla tube vs. to base of corolla tube; stigma lobes 1 mm vs. 6–8 mm long), and structure of thrum flowers (style 2.5–3 mm vs. 4–6 mm long; stigma 0.5 mm vs. 3–4 mm long).

Figures

FIGURE 1. Leptomischus multiflorus, vegetative morphology. A, B. Habit (note weak anisophylly). C. Stem node with stipule and bases of two leaves. From Nuraliev, Lyskov NUR 3486. Photos by M.S. Nuraliev.

FIGURE 2. Leptomischus multiflorus, shoot and inflorescence structure. A. Shoot viewed from below, showing abaxial sides of leaves. B, C. Inflorescences with long-styled flowers. D. Inflorescence with short-styled flowers. From Nuraliev, Lyskov NUR 3486. Photos by M.S. Nuraliev.

FIGURE 3. Leptomischus multiflorus, floral morphology. A, B. Long-styled flower; top and oblique views. C. Short-styled flower; oblique view. D. Postanthetic short-styled flower (corolla abscised), showing style and stigma. E, F. Long-styled flower; side view and longitudinal section. G, H. Short-styled flower; side view and longitudinal section. From Nuraliev, Lyskov NUR 3486. Photos by M.S. Nuraliev.