Rhamnidium riograndense Figueira, 2021

Figueira, Maurício & Schindler, Bianca, 2021, Rhamnidium riograndense (Rhamnaceae), a new species from southern Brazil, Phytotaxa 510 (1), pp. 53-60 : 54-57

Rhamnidium riograndense Figueira , sp. nov., ( Figures 1 and 2 )

Type: — BRAZIL. Rio Grande do Sul: São Pedro do Sul, Cerro do Itaquatiá , 29°36’26.90”S, 54°18’09.70”W, 240 m elev., 13 February 2016, M. Figueira & B. Schindler 464 (holotype RB807913!, isotype CEN116279!, ICN202364!, SMDB19702!) .

The new species is similar to Rhamnidium hasslerianum , differing by a higher number of secondary veins (7–10 pairs vs. 5–6(–7)), tertiary veins slightly prominent and perpendicular to the main vein (vs. flat and reticulate), punctiform glands concentrated on the leaf blade margin and scarse in the rest of the abaxial face (vs. punctiform glands regularly spread and densely disposed in the abaxial face), inflorescences congest (vs. lax), peduncles puberulous up to 2.2 mm long (vs. peduncles glabrous ca. 5 mm long) and hypanthium and sepals externally puberulous (vs. glabrous).

Subshrub with xylopodium, up to 1 m tall; mature branches erect, terete, smooth, slightly flexuous, glabrous or puberulous, reddish-brown; younger branches sub-terete to flattened, smooth to striate, with dark longitudinal lines, puberulous with erect trichomes, light brown. Stipules intrapetiolar persistent, bifid in the apex to almost half of its length, externally puberulous or pubescent, striate, cream in vivo, brown in sicco, 2.0– 3.6 mm long, 1.2–2.0 mm wide at the base, lobes 0.7–1.7 mm long, margins ciliate. Leaves simple, alternate, rarely subopposite or opposite, discolors or concolorous in sicco; adaxial surface pruinose; abaxial surface whitish in vivo; petiole 1.4–3.3 mm long., 0.7–1.8 mm wide in the insertion with the blade, canaliculate, puberulous, pruinose; blade 2.7–8.5 × 0.9–2.8 cm, oblong to oblong-elliptic, rarely oblong-lanceolate, lanceolate or elliptic, margin entire, slightly revolute, apex acute, mucronate, base rounded or subcordate, rarely obtuse, symmetrical, glabrous, with dark punctiform glands concentrated on the margin in both surfaces, scarcely in abaxial surface, chartaceous or subcoriaceous; venation eucampdodromous, main and secondary veins sulcate adaxially, prominent abaxially with conspicuous longitudinal dark lines, secondary veins 7–10 pairs, regularly spaced, ca. 45º, tertiary veins perpendicular to the main vein, slightly prominent. Inflorescence axillary, cymes simple or compound, shortly pedunculate, 0.6–2.2 mm long, (1)3–5(8) flowered; bracteoles at the base of pedicels, deltate, persistent, 1–1.9 mm long., puberulous, castaneous. Flowers monoclinous, 5–merous, pedicelate; pedicels 1.1–2.9 mm long, puberulous; hypanthium 1.6 mm long, puberulous, creamy or greenish-cream, with vinaceous punctiform glands; sepals 1.5–2.0 mm long, deltate, apex acute, costate internally, free above the hypanthium, puberulous, creamy or greenish-cream, with conspicuously vinaceous punctiform glands in vivo, dark in sicco externally; petals 0.8–1.2 mm long, obcordate, shorter than the sepals, cucullate, covering the stamens, white, glabrous; stamens 5, included, inserted above the hypanthium, filaments 0.6 mm long, glabrous, anthers 0.6 mm long, oblong, creamy; ovary superior, 1.1–1.3 × 0.8–1 mm, ovoid, glabrous, bilocular, 1-ovulate per locule; style inconspicuous, estigma sessile. Fruit drupaceous, indehiscent, pedunculate, 1–3 per axil, 0.9–1.1 × 0.6–0.7 cm., pericarp glabrous, reddish-vinaceous, slightly fleshy, obovoid, apex apiculate, apiculum 0.8–1.1 mm long, with 1 pyrene; peduncles 2.5–5.4 mm long. Seeds 1(–2), obovoid, sometimes flattened, oleaginous, testa membranous, maculate.

Comments: —During the analysis of the Rhamnidium specimens collected in Rio Grande do Sul state, only two other samples matching the new species were found. Both are from Jari municipality and were included as paratypes. The first one is a collection by Priest Balduíno Rambo, made in 1942 and previously identified as R. glabrum Reissek (1861: 95) , which is a tree species and never has xylopodium. The second one was made by Alberto Knob and Sérgio Bordignon in 2002, previously identified as R. hasslerianum Chodat (1903: 541) . Rhamnidium riograndrense is morphologically related to R. hasslerianum as both share a subshrub habit with xylopodium, and leaves irregularly distributed, often alternate. However, they differ by a combination of characters as venation pattern, and peduncle size (see key). Besides the morphological differences, the species possess different geographic distribution and ecological preferences. R. hasslerianum is endemic to Paraguay and inhabits sandy soils areas ( Cusato & Tortosa 2013), while R. riograndense occurs in Southern Brazil in rupestrian environments. The new species can be recognized from all other South American species of Rhamnidium because it is a subshrub with xylopodium, glabrous and pruinose leaves, secondary veins 7–10 pairs, congested inflorescences and hypanthium and sepals externally puberulous.

Phenology: — Rhamnidium riograndrense was found in flower in November and in fruit from December to April. The species is deciduous during the winter season.

Etimology: —The specific epithet refers to the restricted distribution of the new species. Currently all known collections are from the state of Rio Grande do Sul, southern Brazil.

Distribution and habitat: — Rhamnidium riograndrense is restricted to the central region of Rio Grande do Sul. It has been recorded in the municipalities of Jari, Santa Maria, São Martinho da Serra and São Pedro do Sul ( Fig. 3 ). The known populations are found between the southern plateau and the central depression regions, in the transition between Parana and Pampean provinces ( Morrone 2014). It grows in steep slopes with solar exposure, 240–400 m elevation, in shallow or litolic soils in xeric environments, sympatrically with species of Dyckia Schultes & Schultes (1830: 65 ; Bromeliaceae ), Parodia Spegazzini (1923: 70 ; Cactaceae ) and other shrubby or subshrubby taxa that present xylopodium as Psidium salutare var. sericeum (Cambess.) Landrum (2003: 1467; Myrtaceae ) and Colletia Comm. ex Jussieu (1789: 380 ; Rhamnaceae ). The ecological preference of xeric habitats is common in Rhamnaceae and adaptations such as spines, reduced blades and reduced size are usually present in the family members, in order to endure in such habitats ( Richardson et al. 2000).

Preliminary conservation status:—The new species is known only by four populations with an Extent of Occurrence and Area of Occupancy of 825 km 2 and 16 km 2, respectively. The individuals of the new species are located in areas that are systematically disturbed by human impact, mostly related to livestock, induced fires and land conversion for annual agricultural crops. Additionally, no known population is in a protected area. In view of the above, R. riograndense can be classified as endangered [EN B1ab(i,ii,iii)+B2ab (i,ii,iii)] according to IUCN criteria (2019). To ensure long term survival of the species, conservation and population monitoring actions are extremely needed.

Additional specimens examined: — BRAZIL. Rio Grande do Sul: Jari p. Tupanciretan, in campestribus dumetosis, 26 January 1942 (fr.), B. Rambo s.n. ( PACA9386 ). Jari , estrada para Quevedos , 29°18’11.0”S 54°10’38.0”W, 369 m elev., 12 November 2011 (fl.), A. Knob & S. Bordignon 7304 ( PACA, UNILASALLE); encosta de morro próxima do arroio Toropi-mirim, 29°21’39.2”S 54°11’13.2”W, 17 January 2020 (fr.), H.M. Büneker 916 et al. ( ICN). Santa Maria, distrito de Santo Antão, 29°37’42.70”S, 54°51’26.40”W, 330 m elev., 24 March 2019 (fl., fr.), M.Figueira & B. Schindler 959 ( CEN, RB) . São Pedro do Sul, Cerro do Itaquatiá, 29°36’26.90”S, 54°18’09.70”W, 240 m elev., 14 May 2012 (fr.), M. Figueira et al. 98 ( CEN, HDCF); Cerro do Itaquatiá, 29°36’26.90”S, 54°18’09.70”W, 240 m elev., 29 January 2016 (fl., fr.), M. Figueira et al. 460 ( CEN, RB, SMDB); Cerro do Itaquatiá , 29°36’26.90”S, 54°18’09.70”W, 240 m elev., 29 January 2016 (fr.), M. Figueira et al. 461 ( CEN, RB); Cerro do Itaquatiá , 29°36’26.90”S, 54°18’09.70”W, 240 m elev., 13 February 2016 (fl., fr.), M. Figueira & B. Schindler 465 ( CEN, ICN, RB, SMDB); Cerro do Itaquatiá , 29°36’26.90”S, 54°18’09.70”W, 240 m elev., 13 February 2016 (fl., fr.), M. Figueira & B. Schindler 466 ( CEN, ICN, RB) .

Figures

FIGURE 1. Rhamnidium riograndense. A. Habit. B. Stipule. C. Leaf, abaxial surface. D. Inflorescence, buds and open flower E. Flower close-up showing petals, stamens and ovary. F. Mature fruit. Drawn by Kelen Pureza Soares based on M. Figueira & B. Schindler 464 (RB).

FIGURE 2. Rhamnidium riograndense. A. Habitat (Cerro do Itaquatiá, Rio Grande do Sul, Brazil). B. Leaf. C. Habit and branch with unriped fruits. D. Xylopodium. E. Branch with flowers. F. Branch with fruits. Photos by M. Figueira and B. Schindler.

FIGURE 3. Geographic distribution of Rhamnidium riograndense.