Stellaria xanthophylla Montesinos & Borsch, 2023

Montesinos-Tubée, Daniel B. & Borsch, Thomas, 2023, Molecular phylogenetics and morphology reveal the Plettkea lineage including several members of Arenaria and Pycnophyllopsis to be a clade of 21 South American species nested within Stellaria (Caryophyllaceae, Alsineae), Willdenowia 53 (3), pp. 115-148 : 139-140

21. Stellaria xanthophylla Montesinos & Borsch , sp. nov. – Fig. 1H , 5G, H , 9 ; Supplementary appendix S14 .

Holotype: Peru, Amazonas, Chachapoyas, Leymebamba , construcciones de piedra, restos arqueológicos La Boveda, 3540 m, 20 Jun 2018, D. Montesinos 6970a ( HSP [ HSP-20000 !]; isotype: B [ B 10 1098616! ]) .

Diagnosis — This species is similar to Stellaria laevis , from which it can easily be distinguished by its leaf margin, which is ciliate in the lower-middle part of the leaf, whereas in S. laevis the margin is completely covered by thin trichomes.

Morphological description — Perennial herb, forming dense mats, 6–10 cm high and up to 20 cm in diam.; root woody. Stems decumbent or more commonly curved, 10–18 cm long, branched; internodes 1–5 mm long, glabrous, sometimes bearing a few trichomes at node base, nodes thickened. Leaves involute, opposite, basally fused, lamina ovate-lanceolate to linear-lanceolate, subtruncate at base and mucronate at apex, stiff or spine-like, 6–8 mm long and 1–1.5 mm wide, glabrous, thick, with midrib prominent, densely covered by thin trichomes at base, tending to be glabrous toward apex; trichomes multicellular, straight or curved, 0.2–0.5 mm long, increasing in length toward base of lamina; older foliage usually covering stems, yellowish in colour. Plants bisexual-hermaphrodite. Flowers perigynous, terminal and axillary, on erect or slightly curved, 5–15 mm long peduncles, bearing tiny protuberances on surface as well as minute trichomes, rarely glabrous, old flowers persistent; calyx cylindrical, imbricate, turbinate, slightly wider at base, 8–10 mm long and 1.4– 2.2 mm wide; sepals 5, lanceolate to narrowly ovate-lanceolate, involute, pale green to dark yellow with age, 5–7 mm long and 1.5–2 mm wide, midrib prominent, margins entire, truncate at base, acute at apex, surface glabrous or nearly so; petals 5, strongly reduced, 2–3 mm long and 1–1.8 mm wide, translucent, elliptical, apex obtuse; stamens 5, 1.5–2 mm long; style 3-fid, less than 1 mm high; ovary cylindrical, 0.9–1.1 mm long and 0.8–1 mm wide, stigma aciculate and obtuse. Capsule ovoid, 0.8–1 mm long, glabrous, containing 4–6 seeds, these ovate, compressed, c. 1 mm in diam., testa maroon, densely tuberculate.

Distribution and ecology — The species is recorded in northern and central Peru, in the mountains adjacent to the Alto Marañón river in Huari province, Áncash department, and in the Utcubamba high mountains river basins in southern Amazonas department, near the boundary with La Libertad and San Martín departments. An additional specimen to the one sequenced comes from the department of Áncash in Peru: Huari, San Pedro de Chaná 4410 m, 5 May 2018, D. Montesinos & G. Sancho 6147 (B-101249409!, HCSM!, HSP-12974!, HUT-62033!, USM!). The habitat varies in vegetation cover and floristic composition but not in precipitation, as these environments tend to receive over 800 mm /year. The typical ecosystem is humid puna grasslands, with rocky outcrops and highland subhumid forest patches with species of Hesperomeles Lindl. ( Rosaceae ) and Verbesina L. ( Asteraceae ).

Etymology — The specific epithet derives from the Greek words xanthos, yellow, and phylla, leaves, referring to the persistent, yellow leaves along the stems of the plant.

Notes — Stellaria xanthophylla shows morphological similarities with S. engleriana but can be differentiated by the following characters: bearing thin trichomes at the base of the lamina (vs. dense trichomes at the base in S. engleriana ); sepal form, size and texture (lanceolate to narrowly ovate-lanceolate, 5–7 mm long and 1.5–2 mm wide, surface and margins glabrous or nearly so in S xanthophylla vs. ovate-oblong, 3–4 mm long and 1–1.5 mm wide, with a ciliate lamina surface and margin in S. engleriana ).

Figures

Fig. 1 (p. 120). Habit in natural environment of some species of the Plettkea clade of Stellaria. – A: S. alpamarcae, Huánuco, Huamalies, 4400 m (Montesinos 5487, CAR440); B: S. congesta, Huánuco, Huamalies, 4200 m (Montesinos 4900, CAR661); C: S. galianoi, Cusco, Urubamba, near Malaga pass, 4240 m, shady rocky slopes in moist grasslands (Montesinos & von Mering 4523, CAR677); D: S. macbridei, Huánuco, Lauricocha, 4790 m (Montesinos 4590, CAR630); E: S. pedunculosa, Moquegua, near Ticsani volcano, 4818 m, pumice slopes (Montesinos & Chicalla 5395d, CAR777); F: S. utcubambensis, Amazonas, Chachapoyas, Leymebamba, Tajopampa, 3700 m, rocky summits of recently burnt slopes (Montesinos & Garcia 4979, CAR433); G: S. weberbaueri, Arequipa, 4876 m, forming cushions with eventually elongated stems (Montesinos & von Mering 4496, CAR670); H: S. xanthophylla Amazonas, S Leymebamba, 3540 m, forming dense mats (Montesinos 6970a, CAR691). – All photographs by Daniel B. Montesinos-Tubée.

Fig. 5. SEM images of seeds of Stellaria species described as new species – A, B: S. apurimacensis; C, D: S. galianoi; E, F: S. utcubambensis; G, H: S. xanthophylla. – Scale bars:A, C, E, G = 0.5 mm; B, D, F, H = 50 μm.

Fig. 9. Morphological details of Stellaria xanthophylla – A: flowering stem; B: stem with leaves; C: leaves; D: mature flowers. – From Montesinos 6970a. – Scale bars: A–D = 1 mm.