Novelties in Oxypetalum (Apocynaceae: Asclepiadoideae): a new species and revalidation of the name O. megapotamicum

Abstract

Based on a specimen collected in Santa Catarina state, Brazil, the new species Oxypetalum kassneri is described and illustrated. Moreover, a molecular phylogenetic analysis allows to propose the revalidation of O. megapotamicum, a species currently placed in the genus Ditassa. The neotype of D. megapotamica and the lectotype of D. oxypetala are designated here.

Key words:
Ditassa megapotamica; lectotypification; neotypification; Oxypetalinae; Oxypetalum kassneri

Resumo

Baseado em um espécime de herbário coletado no estado de Santa Catarina, Brasil, descrevemos e ilustramos uma nova espécie: Oxypetalum kassneri. Além disso, com base em análises filogenéticas moleculares, propomos a revalidação de O. megapotamicum, espécie atualmente circunscrita no gênero Ditassa. O neótipo de D. megapotamica e o lectótipo de D. oxypetala são designados aqui.

Palavras-chave:
Ditassa megapotamica; lectotipificação; neotipificação; Oxypetalinae; Oxypetalum kassneri

Introduction

Oxypetalum R. Br. is the richest genus of Oxypetalinae (Apocynaceae, Asclepiadoideae, Asclepiadeae) with over 130 taxa distributed from Argentina to Mexico, and the Caribbean, but with a center of diversity in Argentina, Brazil, and Paraguay (Ezcurra et al. 2008; Farinaccio & Mello-Silva 2006; Fontella Pereira et al. 2004; Keller & Funez 2017). Although a twining habit is the predominant growth form, around 45% (ca. 60 taxa) are constituted of erect or creeping plants which typically inhabit open environments such as grasslands and marshes.

Out of the 87 species of Oxypetalum recorded in Brazil (Flora do Brasil 2020 under construction), Fontella Pereira et al. (2004) recorded 21 species of Oxypetalum R. Br. in Santa Catarina State, being only nine growing as erect plants. Analysis of a recently collected specimen from São Joaquim (SC), revealed an unprecedented combination of morphological characters among the erect species of the genus, allowing the description of a taxon new to science.

During the study of the Asclepiadoideae of Misiones, Argentina, the morphological evidenced lead to the conclusion that the species known as Ditassa megapotamica (Spreng.) Malme does not fits the concept of Ditassa R. Br. as currently understood in Konno & Fontella Pereira (2004). The basally cordate leaves and the reflexed, slenderly triangular and twisted, yellowish corolla lobes of D. megapotamica are not found elsewhere in Ditassa, but are typical of Oxypetalum, the genus under which the species was firstly described (Sprengel 1827). The availability of a molecular sample allowed to reassess the generic affiliation of the species, confirming the morphological interpretations and the name Oxypetalum megapotamicum Spreng. is restablished and neotypified here. The conspecifity of D. oxypetala Decne., established by Malme (1911) is confirmed and a lectotype for the name is designated here.

Materials and Methods

A high resolution digital camera and stereoscopic microscope were used to obtain images and to study the material of O. kassneri H.A. Keller & Funez and to compile the illustrations.

The chloroplast DNA regions trnT-L and trnL-F intergenic spacers, as well as the trnL and rps16 introns were obtained from a sample of O. megapotamicum Spreng. (Keller 13062, CTES) following the standard procedures described in Liede-Schumann & Meve (2013). The resulting sequences are available in ENA (European Nucleotide Archive) under numbers LR700193-LR700195. These new sequences were then added to “Metastelma DS1” of Liede-Schumann et al. (2014; M15210 in study 12788 of TreeBase (<http://treebase.org/treebaseweb/search/study/summary.html?id=12788>), supplemented by Topeinae, as detailed in Keller & Liede-Schumann (2017). This matrix is aimed to provide a taxonomically broad sampling of Asclepiadoideae with emphasis on New World taxa. The resulting dataset was analyzed with Bayesian Inference (BI) and Maximum Likelihood (ML) using the settings described in Liede-Schumann et al. (2014).

Results

A new Species from Brazil

Oxypetalum kassneri H.A. Keller & Funez, sp. nov. Typus: BRAZIL. SANTA CATARINA: São Joaquim, Morro ao lado do cetrejo, centro de treinamento de São Joaquim, Epagri. 1.232 m, 14.II.2019, fl and fr, A. Kassner-Filho 4778 (holotypus FURB!). Figs. 1; 2a

Figure 1
a-d. Oxypetalum kassneri - a. segment of stem with inflorescence; b. flower; c. pollinarium; d. fruit. Drawing by H.A. Keller (from Kassner-Filho 4778).

Figure 2
a. Stem of Oxypetalum kassneri. b-c. flowers of O. megapotamicum. Photographs: a. Andersson Kassner- Filho (Type plant); b-c. Héctor A. Keller (Keller 13062, CTES).

Quoad habitum, fabricam inflorescentiorum et caput stylare forma ad Oxypetalum crispum Wight ex Hook. & Arn. accedit, sed ab ea differt essentialiter pedicellis longioribus, corola lobis latioribus et corpusculum lanceolatis latioribus.

Erect subshrubs with white latex, 70-100 cm tall; internodes 2.2-5.3 cm long, 1.5-2.2 mm in diam; stems cylindric, pubescent, trichomes erect, multicellular, uniseriate, whitish, 0.2-0.4 mm long. Leaves opposite, petioles c. 2-4 mm long; blades broadly deltoid-ovate on the basal portion of the plant, becoming gradually smaller and narrower toward the apex, 1.8-3.8 × 0.7-3.0 cm, concolorous to slightly discolorous, adaxial and abaxial surfaces pubescent, with trichomes similar to those of the stems; margins entire, base cordate, with 2 conic colleters 0.48-0.52 mm long on adaxial surface; apex acute; venation brochidodromous with 5-7 pairs of secondary veins. Inflorescences extra-axillary, umbelliform, erect, alternate, with 6-9 flowers; peduncles 17-36 mm long × ca. 1 mm diam. pubescent; bracts filiform to linear, pilose, ciliate, 5.2-6.5 × 0.5-1 mm; pedicels 9.7-18 mm long × 0.2-0.3 mm diam., pubescent. Calyx with tube 1.1-1.3 mm; lobes linear-lanceolate, acute, c. 4.7 × 1.3 mm, pubescent on both surfaces, ciliate, 0-2 colleters 0.2-0.4 mm long below the sinus. Corolla tube broadly campanulate, 1.6-1.7 mm long × 3.2-3.7 mm diam., abaxial surface pilose, adaxial surface glabrous, corolla lobes lanceolate 5.2-6.2 × 2.3-3.5 mm, recurved, twisted near the distal third, bright green. Corona white; staminal corona lobes rectangular, 3.0-3.5 × 1.2-2 mm, notched, laterally toothed, each tooth ca. 0.7 × 0.3 mm. Gynostegium sessile. Anthers rectangular, 0.8-0.9 × 0.5-0.6 mm, terminal appendage narrowly ovate, 0.24-0.33 × 0.48-0.68 mm. Corpusculum lanceolate, 0.9-1.1 × 0.2-0.22 mm, caudicles c. 0.20 mm long, with teeth 0.3-0.32 mm long., pollinia falcate, 0.55-0.6 × 0.19-0.25 mm. Style-head pentalobed, 0.8 -0.98 mm long, × 1.35-1.4 mm diam., with filiform appendage 1.3-1.5 mm long, divided at the end into two connivent processes c. 3 mm long. Ovary 1.4-1.5 × 1.3-1.4 mm, hispid. Follicles erect, fusiform, pubescent, 66-74 × 15-18 mm; seeds ovate, 6.2-6.3 × 2.6-2.9 mm, surfaces and margin rugose, brown, coma 24-31 mm long, white.

The epithet is dedicated to the enthusiastic naturalist and botanist Anderson Kassner-Filho (Inventário Floristíco Forestal de Santa Catarina), who collected the holotype of this species.

Only known from the type locality, in São Joaquim municipality, Santa Catarina state, southern Brazil. This species inhabits open grasslands with rocky soil, growing between rocky outcrops. The presence of cattle and recent fire was observed in the locality. The high altitudinal grasslands of “Aparados da Serra Geral” region, between Santa Catarina and Rio Grande do Sul states, are extremely rich in vascular plant endemics (Hassemer et al. 2015). However, they are rapidly giving way to destructive livestock, agriculture, and silviculture practices. The lack of legal protection in most of this region is a crucial aspect that, if not urgently changed, will lead to the extinction of some of the endemic species.

The only collection of this species shows floral buds, flowers and fruits during the summer, in February.

Some erect Oxypetalum R. Br. species have prominent corona lobes that completely hide the body of the gynostegium, but reveal part of the style-head appendage, which protrudes above the apex of the corona lobes. From the species with such characteristics, the one that most closely resembles O. kassneri is O. crispum, as both species possess broad leaves, many-flowered, long-pedunculate inflorescences, toothed caudicles and a style-head appendage divided at the end into two connivent processes. However, O. kassneri has longer pedicels and wider corolla lobes than O. crispum. Moreover, the corpuscle is linear oblong in O. crispum, while it is lanceolate in O. kassneri.

Among erect species of Oxypetalum R. Br. with toothed caudicles, only a few have a lanceolate corpusculum. O. kassneri differs from these by its non-linear leaves, by its corona lobes without ligule, and by its peduncle of more than 1.5 cm. long

Oxypetalum megapotamicum Spreng., Syst. Veg., 4(2) (Cur. Post.): 111. 1827. Ditassa megapotamica (Spreng.) Malme., Bull. Soc. bot. Genève, 2(3-4): 270. 1911. Type: Brazil. F. Sellow 821 (neotype NY [NY00279078], designated here; isoneotype K [K000095572]).

= Ditassa oxypetala Decne., in Candolle., Prodr. 8: 574. 1844. Type: Brazil. Rio Grande, 1833, Gaudichaud 699 (lectotype P [P00252620], designated here).

Material examined: ARGENTINA. CORRIENTES: Bonpland, 15.I.1908, E.L. Ekman 409 (NY). MISIONES: Oberá, Ruta Prov. 103, de San Martín a Mártires, 200 m, 26.IX.1997, fl, F. Zuloaga & O. Morrone 6515 (SI); L.N. Alem, Caá Yarí, 27°30’23,5’’S, 55°17’34,8’’W, 176 m, 06.X.2012, fl, H.A Keller et al. 4541 (CTES). San Ignacio, Caá Yarí, 27°17’08,9’’S, 55°25’09,5’’W, 166 m, 22.X.2015, fl, H.A Keller 6, M.M. Franco 4541 (CTES). Cainguás, Predio UNLP, Reserva Privada, Campito 5, 27°06’56’’S, 54°59’19’’W, 17.III.2000, fl, F. Biganzoli et al. 923 (SI). BRAZIL. 1882, Sellow 175 (NY); Sellow 821 (NY). PARANA: Calmon, 15.III.1910, fl and fr, P. Dusén 9322 (GH, S). RIO GRANDE DO SUL: Cachoeiras, 01.I.1902, fr, Malme 925 (S). SANTA CATARINA: Urubici, Parque Nacional de São Joaquim, Santa Bárbara, estrada para a cascatinha, 28°08’47’’S, 49°36’48’’W, 1.400 m, 25.I.2019, fl, L. Funez et al. 8702 (FURB). Chapecó, Fazenda Capo Sao Vicente, 900-1.000 m, 26.XII.1956-28.XII.1956, fl, L.B. Smith, R. Reitz & O. Sufridini 9462 (NY). Campo de Capivare, Serra Geral, I.1891, fl, E. Ule 1846 (HBG). URUGUAY. SORIANO: Juan Jackson, Sta. Elena, X.1939, fl, J.P. Gallinal et al. PE-4292 (NY).

Iconographies and extended descriptions were observed in Fournier (1885: 251, tab. LXXI fig. 1), Meyer (1944: tab. LXXV), Fontella Pereira et al. (2004: 155-156, Plate 38).

The geographic distribution is Brazil (Goiás, Paraná, Rio Grande do Sul, Santa Catarina, São Paulo), Argentina (Misiones) and Uruguay (Montevideo, San José, Soriano).

Oxypetalum megapotamicum was described on samples not specified by Sprengel (1827), but whose location corresponds to “Rio Grande, Brazil”. However, the only specimens from this area still extant are Gaudichaud 698 ([P00252619], P) and 699 ([P00252620], P), that were later used by Decaisne (1844) to describe Ditassa oxypetala Decne., which is lectotypified here on the the specimen [P00252620] bearing a hand-written description. Therefore, the specimen [NY00279078], that bears an original stamp of “Mus. bot. Berol.”, the herbarium in Berlin (B), and might have been seen by Sprengel, in whose collection Sellow specimens were found (fide Stafleu & Cowan 1976-1988, online edition: <https://www.sil.si.edu/DigitalCollections/tl-2/browse.cfm?vol=5#page/820>), is selected as neotype here. A duplicate of this specimen is housed in K, [K000095572], but it only bears the label, not the stamp of B, and is therefore regarded as an isotype.

Some decades later, Malme (1911: 270) proposed the combination Ditassa megapotamica (Spreng.) Malme. and put Ditassa oxypetala Decne. into synonymy. A sequenced DNA sample now documented that the species is to be placed in Oxypetalum R. Br. (Fig. 3); so here we propose to restore the name originally established by Sprengel (1827).

Figure 3
Position of Oxypetalum megapotamicum in the subfamily Asclepiadoideae. Recognized tribes and subtribes without new accessions are summarized by triangles and those restricted to the New World are shaded grey. Numbers indicate Maximum Likelihood bootstrap support (BSML)/Bayesian Posterior Probability (PP); groups with BSML > 95 and PP = 1.0 are indicated by bold lines.

This taxon must not be confused with Physianthus megapotamicus Spreng. (a synonym of Araujia megapotamica (Spreng.) E.Fourn.). Therefore, the lectotypification of Lagenia E.Fourn. on L. megapotamica (Spreng.) E. Fourn. (Rapini et al. 2011) needs to be corrected, from “(Sprengel 1827: 111)” which refers to Oxypetalum megapotamicum to “(Sprengel 1827: 112)” which refers to Physianthus megapotamicus.

The taxonomic placement of this taxon in Ditassa R. Br., proposed by Decaisne (1844) and Malme (1911), possibly responds to the pollinaria with edentate caudicles, corona lobes with internal lobulate processes (ligule) (Fig. 2c) that give the appearance of a “double corona” and the absence of style-head appendages. In contrast, however, the basally slightly cordate leaves and corolla lobes twisted anti-clockwise are not found in other Ditassa species.

The absence of style-head appendages is rare in the genus Oxypetalum R. Br. and has been used as specific epithets such as O. muticum E. Fourn. or to the conformation of other recently synonymized genera such as Rhyssostelma Decne. (Liede-Schumann & Meve 2015). However, in the resulting phylogenetic tree (Fig. 3), O. megapotamicum forms a well supported group with O. sylvestris Hook. & Arn. and O. pentasetum (Rusby) Goyder & Rapini. These species were included in Schistogyne Hook. & Arn., a genus of eight species now combined in Oxypetalum by Rapini et al. (2011). Schistogyne is characterized by stigmatic appendages with 5-7 filiform branches and untoothed caudicles (Ezcurra et al. 2008; Fontella Pereira et al. 2004; Hechem & Ezcurra 2006; Meyer 1944) so that the absence of stigmatic appendages in O. megapotamicum is possibly due to a reversal of the apomorphic filiform branches of the style-head.

Acknowledgments

The authors thanks to Anderson Kassner-Filho, for the field photograph and some field data about this species. L.A.F. thanks to Conselho Nacional de Desenvolvimento Científico e Tecnológico [153430/2018-4]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior; Brazilian Program for Biodiversity Research (PPBio) Atlantic Forest Network [CNPq 457451/2012-9]; CNPq/Capes/FAPs/BC-Fundo Newton/PELD [number 15/2016], for the scholarship.

References

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Edited by

Area Editor: Dr. Marcelo Trovó

Publication Dates

• Publication in this collection
  08 Mar 2021
• Date of issue
  2021

History

• Received
  23 Sept 2019
• Accepted
  25 Dec 2019