Stellaria utcubambensis 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 : 137-138

18. Stellaria utcubambensis Montesinos & Borsch , sp. nov. – Fig. 1F , 5E, F , 8 ; Supplementary appendix S13.

Holotype: Peru, Amazonas, Chachapoyas, Leymebamba, Tajopampa Camino Inca , 3696 m, 14 Aug 2016, D. Montesinos 4979 ( HUT [ HUT-60181 !]; isotypes: B [ B 10 0766222 !], O [ O-227246 !], USM!).

Diagnosis — The species can be easily distinguished from the other members of the clade by the stiff linear-lanceolate leaves and the prominent calyx apex that forms a needle-like stiff point, a feature that is not seen in any other species.

Morphological description — Perennial herb, forming mats 2–4 cm high and 10–30 cm in diam.; roots fibrous. Stems suberect or decumbent to prostrate, trailing, densely ramified at base, clothed with older leaves down to base; internodes 2–4 mm long, nodes slightly thickened, glabrous, yellowish. Leaves opposite, narrowly involute or plane, eventually curved with age, lamina linear-lanceolate, stiff and coriaceous, truncate at base and aristulate-acuminate near apex, 4–6 mm long and <1 mm wide, glabrous on both sides, midrib prominent on underside, margins glabrous toward apex, basally with 0.1–0.3 mm long trichomes. Plants bisexual-hermaphrodite. Flowers perigynous, terminal and axillary, always suspended on 2–5 mm long, erect and glabrous peduncles; calyx cylindrical, 4–6 mm long and 0.8–1.1 mm wide; sepals 5, ovate-lanceolate, 4–6 mm long and c. 1 mm wide, involute, glabrous on both sides except at base of margins, where minute c. 0.1 mm long trichomes are present, truncate at base and cuspidate at apex, midrib excurrent as a thin 0.1–0.25 mm long needle, surface greenish-white turning yellowish with age; petals 5, deeply bifid, bright white, ovate-elliptical, in total 7–10 mm long, lobules ovate-lanceolate 0.3–0.6 mm long and 0.3–0.5 mm wide; filaments c. 0.4 mm long, stamens 5–10, episepalous, c. 0.4 mm long, anthers 0.1–0.2 mm long, styles 3-fid, ovary ovoid, 0.2–0.3 mm long and c. 0.3 mm wide. Capsule ovoid or nearly so, 0.6–0.8 mm long and c. 0.5 mm wide, containing 3 seeds, these roundish or nearly so, flattened, 0.4–0.5 mm in diam., testa dark maroon to blackish, covered with rectangular stellate tubercules.

Distribution and ecology — The species inhabits the mountain summits of the tributaries leading to the Utcubamba river in the Amazonas department in N Peru, with an expected growth at altitudes of 3600–3900 m. The species was found in areas where slope burning is an unfortunate practice applied by the local people; such events and climate change could lead to the gradual disappearance of this species. Flowering has been observed during the months of September and November.

Etymology — The specific epithet refers to the Utcubamba river in N Peru that divides Amazonas department from south to north. The new species was found in its uppermost tributaries, and it is very likely that there are further populations on the mountains draining into this river.

Notes — This species is known so far from only one collection, but further populations might be encountered after searching in the field. Stellaria utcubambensis differs from S. apurimacensis by having leaves stiff, linear-lanceolate and with margins glabrous toward apex (vs. weak, elliptical-lanceolate and with margins sparsely pilose in S. apurimacensis ). Moreover, the internodes in S. utcubambensis are 2–4 mm long (vs. 4–10 mm long in S. apurimacensis ) and the calyx is cylindrical (vs. campanulate in S. apurimacensis ).

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. 8. Morphological details of Stellaria utcubambensis – A: ramified stems with flower; B: leaves; C: mature flowers; D: flower capsule; E: tuberculate seeds. – Montesinos 4572. – Scale bars:A–C = 1 mm; D = 0.5 mm; E = 200 μm.