Argostemma sawmlianae Lalhlupuii, Tlanhlui, S. D. Khomdram & S. D. Yumkham, 2025

Lalhlupuii, Margaret, Tlanhlui, Lal, Khomdram, Sandhyarani Devi & Yumkham, Sanatombi Devi, 2025, Argostemma sawmlianae (Rubiaceae, Argostemmateae), a new species from Northeast India under the Indo-Burma Hotspot, PhytoKeys 266, pp. 317-328 : 317-328

Argostemma sawmlianae Lalhlupuii, Tlanhlui, S. D. Khomdram & S. D. Yumkham sp. nov.

Figs 1 , 2 , 3

Type.

India. • Mizoram, Aizawl district, Lungleng village , 23.66581, 92.66353, 1003 m alt., 05 July 2022, Lalhlupuii 128870 ( holotype: ASSAM!; isotype: MZUH!, MUMP!) .

Diagnosis.

It is similar to Argostemma courtallense Arn. and A. sarmentosum Wall. , but differs from the two in having one pair of larger sessile leaves ( 11.5–18.5 cm long), longer peduncle ( 4–6.5 cm long), more flowers per cyme (8–33), and campanulate corolla with falcate petals which are reflexed and strongly rolled backwards (Fig. 3 , Table 1 ).

Description.

Epilithic, perennial herb, 7–17 cm tall, attached to substratum with dense, much-branched, non-tuberous matted roots. Stem semi-erect, terete, unbranched, 1.5–7 cm long, greenish white, pubescent. Leaves opposite, strongly anisophyllous, paired, sessile, reticulate eucamptodromous, secondary veins 6, ovate, 11.5–18.5 × 10–13.3 cm, base cordate, margin entire, apex acute, pubescent on both sides; small pair of rudimentary leaves, sessile, broadly ovate to elliptic, 3–7 × 3–4 mm, green, pubescent. Stipule sessile, ovate, 5–7 × 3–4 mm, base cordate, apex acute, green, margin pubescent. Inflorescence umbelliform, flowers basipetal, single, rarely 2–4, 8–33 flowered. Bracts foliaceous, 4–6, fused, unequal size, whorled, elliptic to ovate, 8–11 × 4–6 mm, green, margin pubescent, whorled, isomorphic with number of inflorescences (1–4); peduncle 4–6.5 cm long, greenish white, glabrous. Flowers pedicellate, 4 - merous, actinomorphic, 1.8–2.2 cm, pedicel 7–10 mm long, white, pubescent. Calyx 4 - lobed, lobes basally connate, ovate, 6–10 × 4–5 mm, petaloid, white, calyx teeth tip green, become completely green after anthesis, glabrous. Corolla 4, white, falcate, 6–8 × 2–3 mm; ¾ lobes reflexed, tube green blotched, 1–2 × 1–3 mm, tuff haired at tip of corolla lobe. Stamens 4, equal, anthers free, loosely arranged, basifixed, 6 mm long, yellow, exserted from the corolla tube, glabrous; filaments 2–3 mm, free, S-like curvature, white.

Style 1–1.2 cm long, white, glabrous; stigma club shaped, yellow; ovary inferior, bilocular, axile placentation, hairy; ovule numerous, yellow. Seeds numerous, minute, triangular, 600 × 300 μm, black, testa reticulate, central mamilla in each cavity (Fig. 2 D, E ).

Pollen grains.

Monad, heteropolar, very small 8–9 × 8–9 µm, triangular amb, isodiametric (P / E ratio 1), triradiate colpi (dry) (Fig. 2 F ).

Phenology.

Flowering from June – July and fruiting from July – August.

Distribution and ecology.

The plant was found growing on a damp rock-wall along a stream with mosses, pteridophytes ( Selaginella sp. , Asplenium sp. ) and Begonia spp. ( Begoniaceae ). The plant was collected from Lungleng village in Aizawl District of Mizoram, India which is located at 23°39'57"N, 92°39'41"E, south of Aizawl city. Positioned at an elevation of 1011 m above sea level, Lungleng receives an average annual rainfall of about 2500 mm, with temperature ranging from 26 ° C – 31 ° C. The settlement lies atop a hill and is encircled by a narrow belt of dense community reserve forest comprising subtropical broad-leaved evergreen mixed forest and with patches of secondary forest surrounding the reserved area.

Conservation status.

The newly described species was found growing as a lithophyte at its type locality only, represented by a single population of 39 mature individuals which are less than 50. The habitat which is situated along a roadside faces significant threats from frequent landslides and ongoing developmental activities such as road construction and expansion. The estimated area of occupancy ( AOO) is less than 10 km 2. Based on current field observations, the species is provisionally assessed as Critically Endangered [ CR B 2 ab (ii, iii, v) c (ii, iii, iv) D] according to the IUCN Red List Categories and Criteria ( IUCN 2024). Further research is necessary for thorough and long-term population assessment to yield a more precise conservation evaluation.

Etymology.

The specific epithet sawmlianae is to honour Mal Sawmliana, a forest conservator and naturalist, as a recognition of his efforts and contribution in exploring the flora and fauna for conservation measures in Mizoram.

Suggested common name.

Sawmliana par (Mizo)

Molecular studies of Argostemma sawmlianae

After analysis of the matK and ITS 2 sequences from Argostemma sawmlianae , it was observed that the consensus length of the matK sequence is 766 bp with 29.51 % G: C content and that of ITS 2 is 438 bp with 52.69 % G: C content. A Maximum Likelihood ( ML) tree was constructed using matK and ITS 2 sequences in MEGA X (Molecular Evolutionary Genetics Analysis, X) to analyze the placement of A. sawmlianae among different members of Rubiaceae with Cinchona officinalis as an outgroup species (Figs 4 , 5 ).

Phylogenetic analyses based on matK and ITS 2 regions of the newly described species and available database from NCBI (Suppl. material 1: table S 1) confirmed the placement of the newly described species within Argostemma ( Rubiaceae ). These findings align with Bremer (2009), who established the monophyly of the Rubiaceae family. The matK phylogenetic tree shows that A. sawmlianae clusters closely with A. hookeri King and A. yappii King , supported by bootstrap values ranging from 45 to 98. Similarly, in the ITS 2 phylogenetic tree, A. sawmlianae forms a well-supported clade with A. yappii (bootstrap 85), together constituting a distinct Argostemma group. The genomic data for allied taxa Argostemma courtallense Arn. and A. sarmentosum Wall. were not available in the NCBI database, and therefore, these species could not be included in the phylogenetic analysis.

Figures

Figure 1. Argostemma sawmlianae Lalhlupuii, Tlanhlui, S. D. Khomdram & S. D. Yumkham, sp. nov. A, B. Habit; C. Anisophyllous leaves with inflorescence (inverted view); D. Leaf with stipule; E, F. Anisophyllous leaves; G. Flower with bract; H. Inflorescence; I. Foliaceous bracts; J. Rudimentary leaves; K. Petaloid calyx with green tips; L. Corolla with green blotched tubes; M. Corolla with reflexed and backwardly rolled lobes; N. Single falcate shaped corolla lobe; O. Corolla lobes; P. Single stamen with curved filament; Q. Androecium with loosely arranged stamens. (photos by Margaret Lalhlupuii & Lal Tlanhlui).

Figure 2. Argostemma sawmlianae Lalhlupuii, Tlanhlui, S. D. Khomdram & S. D. Yumkham, sp. nov. A. Single flower; B. Pistil; C. Cross section of ovary; D. Seeds (LM image); E. Seed (SEM image); F. Pollen (SEM image); G. A. sawmlianae in type locality; H, I. A. verticillatum from Manipur; J. A. kamjongense from Manipur; K. A. sarmentosum from Meghalaya. (photos by Margaret Lalhlupuii, Lal Tlanhlui & Yumkham).

Figure 3. A. Holotype of Argostemma sawmlianae Lalhlupuii, Tlanhlui, S. D. Khomdram & S. D. Yumkham, sp. nov. (Lalhlupuii 128870, ASSAM!); B. Herbarium Specimen of A. courtallense [K 000030994] (reproduced with permission from http://specimens.kew.org/herbarium/K000030994); C. Herbarium specimen of A. sarmentosum [K 000030998] (reproduced with permission from http://specimens.kew.org/herbarium/K000030998); D. Herbarium specimen of A. sarmentosum [MUMP 001591]

Figure 4. Phylogenetic tree of Argostemma sawmlianae reconstructed based on Maximum Likelihood (ML) as a cladistic method comprising 31 matK nucleotide sequences using MEGA X. Red solid circle indicates the placement of A. sawmlianae among A. hookeri, A. yappi and Argostemma sp. in the phylogenetic tree.

Figure 5. Phylogenetic tree of Argostemma sawmlianae reconstructed based on Maximum Likelihood (ML) as a cladistic method comprising of 27 ITS 2 nucleotide sequences using MEGA X. Red solid circle indicates the placement of A. sawmlianae with A. yappi in the phylogenetic tree.