Euphorbia pedersenii Subils (1971: 238)

Külkamp, Josimar, Silva, Otávio Luis Marques Da, Valduga, Eduardo, Iganci, João Ricardo Vieira, Cordeiro, Inês & Baumgratz, José Fernando A., 2018, First record of Euphorbia pedersenii Subils (Euphorbiaceae) for Brazil, Phytotaxa 379 (4), pp. 287-292 : 288-291

Euphorbia pedersenii Subils (1971: 238)

TYPE:— ARGENTINA. Corrientes: Dpto. Mercedes, Justiniano Solar , vegeta [sic!] campos de pastoreo, 8 March 1945, T.S. Ibarrola 2608 (holotype LIL; isotype SI005011!). Figure 1 .

Description: —Perennial hemicryptophyte herb, 10–40 cm tall, erect, mostly glabrous, except for the ovary/fruit; root 3–6.5 × 1–1.7 cm, tuberous, elongated, unbranched; latex milky; branches glabrous; leaves simple, alternate, subsessile, lamina 20–35 × 1.5–3.3 mm, lanceolate, base attenuate, apex acute, margin dentate, glabrous, only the central vein evident and well visible; stipules absent. Cyathia arranged in terminal pseudodichasia; involucre campanulate, 1.8–2 × 1.5–2.1 mm, lobes rectangular, with 3-dentate apex, margin ciliolate; glands 4 per involucre, green, trapezoidal; bracteoles 3-laciniate; staminate flowers 10–15, anthers yellow; pistillate flowers with a 3-partite perianth-like whorl, ovary puberulous, trichomes simple, styles bifid. Fruits with recurved pedicels; capsules 2–2.4 × 2.5–3 mm, subglobose, with sharp angles and scattered simple short (<0.5 mm) trichomes, denser along the ribs; seeds 1.8–2 × 1.4–1.6 mm, 3 per capsule, smooth, ecarunculate.

Notes: —These first records of Euphorbia pedersenii from Brazil expand the geographical range of this species from Corrientes Province, in northern Argentina, to southern Brazil. In Argentina, the earliest collected specimen was made in 1945 by T.S. Ibarrola 2608, followed by additional T.M. Pedersen 1770 (CTES [photo!]), 3909 (CORD [photo!], CTES [photo!], US [photo!]), 5839 (CORD [photo!], CTES [photo!]) and s.n. (CTES [photo!]) each from a distinct location, but still in Corrientes, collected in the 1950s and 1960s. When Subils (1971) analyzed these specimens, they were deposited in the personal herbarium of botanist Troels Myndel Pedersen (TMP). Subsequently, these collections were incorporated into the CTES herbarium, where they are found today. Subils (1971) compared E. pedersenii to E. pampeana and E. stenophylla , stating that it is distinguished by its leaf shape (not supported later, since all of them have lanceolate leaves [ Subils 1971, 1977]) and arrangement of cyathia (pseudodichasia in E. pedersenii and pseudopleiochasia in E. pampeana and E. stenophylla ). However, the indumentum of the ovary and fruit is very useful to distinguish E. pedersenii from these two species.

The first records for Brazil come from the State of Rio Grande do Sul ( Fig. 2 ), approximately 230 km from the northernmost point of the species in Argentina. The specimens were collected in early November with mature fruits, although the plants still had a few flowers. The occurrence of E. pedersenii raises the number of species of E. sect. Nummulariopsis in Brazil to ten, making it one of the most representative lineages of Euphorbia in the country, surpassed only by E. sect. Anisophyllum Roeper (in Duby 1828: 412), with 27 species.

Initially, the specimens collected in Rio Grande do Sul were compared with other Euphorbia species occurring in this state. At first, we observed a close morphological affinity with E. pampeana , as also indicated by Subils (1971). However, analyzing the taxonomic treatment of Subils (1977), the protologues and type specimens, we confirmed that the specimens belong to E. pedersenii , mainly by characteristics of the root, cyathial arrange, glands shape, and ovary and fruit indumentum. Measuring the specimens collected in Brazil, we extended the original description by the presence of individuals smaller than 20 cm in height and with smaller roots and leaves; the remaining measurements are in agreement with the diagnostic characters described in the protologue.

Euphorbia pedersenii is similar to E. pampeana due to habit, tuberous roots, four flat glands in the cyathium and glabrous leaves and branches. However, E. pedersenii has cyathia arranged in pseudodichasia, with 2 lateral branches (vs. pseudopleiochasia, i.e., with 3 or more lateral branches), elongated tuberous root (vs. ovoid tuberous root), trapezoidal glands (vs. semicircular), and puberulous ovary and fruit (vs. glabrous). Another similar species is Euphorbia stenophylla , which shares lanceolate leaves with dentate margins. However, this species may be distinguished by its cyathial arrangement in pseudopleiochasia (vs. pseudodichasia), and ovary and fruit glabrous (vs. puberulous).

Habitat and distribution:—In Brazil, Euphorbia pedersenii occurs in a habitat similar to that found in Argentina, that is, restricted to rocky grassland with shallow soils ( Fig. 1A ). Probably, it is resistant to frost in the winter and fire during dry periods due to the tuberous nature of the roots, which allows it to survive in unfavorable conditions, when likely the aerial parts of plant die off. Specimens were collected in the ecotone between the Pampa and Atlantic Forest domains (Külkamp et al. 414, 416), and in the core area of the Pampa (Queiroz 12499). Due to the environmental and climatic similarities shared by the population sites, we believe that it could be found in other localities of the Província Pampeana and Província del Espinal ( Cabrera & Willink 1973). The small size of E. pedersenii , which makes it hard to find among the grass coverage of the habitats, and the probable fall of the aerial portion during the frozen and dry periods may explain the low number of specimens in herbaria.

Conservation status: —In Brazil, only three collections Euphorbia pedersenii are known, from two municipalities in western Rio Grande do Sul state, which are approximately 230 km apart. Populations from Bossoroca municipality are located on private farms with cattle grazing. This region is undergoing a major advance in the transformation of native fields (Pampas) to monoculture. The areas where the species was found are inappropriate for agricultural mechanization, in this way the conservation of the species is less compromised, however, Eucalyptus forestry and soy beans cultivation have increased rapidly in the region.

The total geographical range of E. pedersenii is severely fragmented due to anthropic pressure, representing a barrier to a possibly more continuous distribution range. We estimated an AOO (Area of Occupancy) of 32 km ², and EOO (Extent of Occurrence) of ca. 66,750 km ². Thus, the species is categorized as Vulnerable (B2ab[iii]) due to an AOO of <500 km ², severely fragmented populations (despite the few known locations) with small number of individuals, habitat specificity, and the continuing decline in the quality of habitat due to conversion of native fields to monoculture.

Specimens examined: — BRAZIL. Rio Grande do Sul, Bossoroca, São Marcos , em campo entre afloramento rochoso, 28°50’36”S, 54°43’33.5”W, 2 November 2017, J. Külkamp et al. 414 (ICN, SP) ; Bossoroca, São Marcos, em lajeado com musgos, 28°52’49”S, 54°56’26.5W, 2 November 2017, J. Külkamp et al. 416 (ICN, RB). Santana do Livramento , ca. 40 km N de Santana do Livramento na estrada para o Passo dos Mineiros, campo com capões de mata ciliar, 30°36’08”S, 55°33’55”W, 15 November 2006, L.P. Queiroz 12499 (HUEFS) .

Figures

FIGURE 1.Euphorbia pedersenii.A, Rocky grasslandwhere the species growsin Rio Grande do Sul, Brazil; B, Habit with its characteristic underground system; C, Detail of stem with cyathium and fruit. Photos by J.Külkamp.

FIGURE 2. Distribution map of Euphorbia pedersenii. Red triangles: new records of E. pedersenii in Brazil; black circles: the known records of E. pedersenii in Corrientes, Argentina.