Two new species of Euphorbia sect . Nummulariopsis ( Euphorbiaceae ) from South America

Carrillo-Reyes, P. & Steinmann, V.W. 2011. Two new species of Euphorbia sect. Nummulariopsis (Euphorbiaceae) from South America. Anales Jard. Bot. Madrid 68(2): 167-173. Two new species of sect. Nummulariopsis, Euphorbia guaraniorum and E. cordeiroae, are described and illustrated. Euphorbia guaraniorum appears to be related to E. portulacoides and is distinguished by its densely arranged ensiform leaves. It is known only from the Yacyretá and Ybycui Islands in southern Paraguay. Euphorbia cordeiroae, occurs in the state of Goiás, Brazil, and is similar to E. stenophylla, from which it differs in its higher stature and very narrow and loosely arranged leaves.


Introduction
Euphorbia L. sect.Nummulariopsis Boiss., as here circumscribed, contains approximately 30 species and has a disjunct distribution between the southeastern United States and South America.The section was initially proposed for Euphorbia peperomioides Boiss., a Brazilian endemic, but molecular phylogenetic results demonstrate that this species is nested within a clade that otherwise corresponds to Euphorbia sect.Tithymalus Boiss.subsect.Inundatae G.L. Webster (Steinmann & Porter, 2002).Nummulariopsis is the oldest legitimate name at the rank of section, and it is here adopted and expanded to include species previously treated with sect.Tithymalus subsect.Inundatae.As discussed by Webster (1967), the species in this group were first treated within Euphorbia sect.Tithymalus subsect.Ipecacuhuanae Boiss.(Boissier, 1862), but they are not closely related to the type of this section, Euphorbia ipecacuhuanae L. It is worth noting that E. peperomioides differs vegetatively from the remainder of the species in the group by possessing a strictly prostrate habit with opposite leaves and stems rooting at the nodes.However, in terms of cyathial morphology, it is indistinguishable from the others.The distinctive feature of this section is the presence of perianthlike lobes that terminate the gynophore.This condition is very rare in Euphorbia and appears to represent a synapomorphy for sect.Nummulariopsis.Other characteristics of this section include the herbaceous habit, involucral glands lacking appendages, and ecarunculate seeds.According to molecular phylogenetic analyses (Steinmann & Porter, 2002), sect.Nummulariopsis is inferred to be the sister clade to E. germainii Phil.(sect.Portulacastrum) and belongs to Euphorbia subg.Euphorbia, sensu Bruyns & al. (2006).
During the course of revisionary studies on sect.Nummulariopsis, as part of the collaborative Planetary Biodiversity Inventory (PBI) Euphorbia project (Esser & al., 2009), two undescribed species were encountered.The purpose of this article is to formally propose them as new and provide comments on their distribution, ecology, and relationships.

Phenology, habitat and distribution
Euphorbia guaraniorum flowers from August to November.It is known from a few collections from Yacyretá and Ybycui Islands in southern Paraguay.The new species has been found on sandy hillocks at approximately 80 m elevation in the transition zone between mesophyllous forest and a community locally known as "pajonal", a mesophyllous grassland dominated by Elyonurus muticus (Sprengel) Kuntze (Fontana, 2008;2010 pers. com.).Yacyretá Island was heavily impacted by the construction of the Yacyretá dam.More than two thirds of its original area was flooded, and some populations of E. guaraniorum have likely been destroyed.However, the type collection was made in the western portion of the island after the initial flooding, and this area now composes the Yacyretá Island Reserve, a compensatory natural protected area (Quintero, 2007).The presence of Euphorbia guaraniorum in fluvial sandy environments in adjacent Argentina (Corrientes and Misiones Pro vinces) is possible and should be explored.
Etymology.The specific epithet honors the Guaraní indigenous people, who inhabit the area where the new species occurs.Euphorbia guaraniorum is a distinctive species by virtue of its densely arranged ensiform leaves.Its closest relative seems to be E. portulacoides L., with which it shares cyathial features such as the campanulate involucre and the thick, broadly reniform, dark-red glands.However they can be separated by the disposition, shape and width of cauline leaves: Euphorbia portulacoides has loosely arranged, broadly elliptic cauline leaves that are 5-15 mm wide, whereas E. guaraniorum possesses densely arranged, ensiform cauline leaves less than 4.5 mm wide.

Phenology, habitat and distribution
Euphorbia cordeiroae flowers from October to March.It is a narrow endemic from the region of Chapada dos Veadeiros, in northeastern Goiás State, where it occurs between 1170 and 1250 m in elevation.According to Munhoz & Proença (1998), the vegetation of the area corresponds to cerrado sensu stricto, a savanna-like biome characterized by remarkable floristic diversity with a high concentration of endemic subshrubs and herbs.
Etymology.The specific epithet honors Dr. Inês Cordeiro, a Brazilian botanist from SP who collected the type specimen.Euphorbia cordeiroae is a remarkable species due to its tall, slender stem (to 70 cm tall), linear leaves with entire margins, and cyathia arranged in loose pseudopleiochasia.Apparently, its closest relative is E. stenophylla Boiss., another narrow-leaved species that also occurs in Brazil.However, E. stenophylla possesses shorter stems (to 30 cm tall) and ensiform leaves with denticulate margins.A comparison between these two species is provided in Table 1.Both species are also geographically separated, with E. cordeiroae occurring only in the Planalto area of central Brazil (Goiás) at elevations of 1170-1250 m, and E. stenophylla is distributed in southern Brazil (Rio Grande do Sul and Paraná), Argentina, and Uruguay (Subils, 1977;Bacigalupo, 2005), at elevations of 200-1000 m.

Fig. 2 .
Fig. 2. E. guaraniorum:A, detail of the inflorescence.The whitish pubescence shown here is not part of the plant, but some kind of insect or spider silk; B, habit.Photographs by J. Molero.