Introduction

Oldenlandia corymbosa L. is a member of the Rubiaceae family, which includes about 650 genera and more than 13,765 species worldwide (Robbrecht & Manen, 2006; ^{Govaerts et al., 2022}). The genus Oldenlandia L. occurs throughout the tropical and warm subtropical regions of the world, with its largest diversity in Africa (^{Halford, 1992}). It is characterized by the loculicidal capsule dehiscence and “oldenlandioid” seeds (trigonous with a reticulate or reticulate areolate testa) (Terrell, 1990). The number of species in the genus is hard to estimate (^{Neupane et al., 2015}) due to inconsistencies in genera delimitation in the tribe Spermacoceae, resulting in a taxonomic complex formed by Oldenlandia, Hedyotis L., and other smaller genera from the tropics of the Asia-Pacific region. Oldenlandia corymbosa is the type species for the genus and it has been extensively studied from a phytopharmacological point of view because its uses in traditional medicine in India and China (Patel et al., 2014). This species is native to Africa and South Asia, and is currently naturalized in tropical and subtropical regions of the world (Terrell & Robinson, 2006; ^{Delprete et al., 2005}; Sánchez Rodríguez et al., 2007; Shahid & Rao, 2014).

In the Americas, O. corymbosa was previously recorded as naturalized and well-established in Brazil (^{Delprete et al., 2005}; Flora do Brasil, 2021), Jamaica (^{Adams, 1972}), USA (Terrell & Robinson, 2006), and Venezuela (Taylor & Steyermark, 2004). While doing fieldwork for a revisionary study of Oldenlandia in South America (Nuñez Florentin, in prep.), O. corymbosa was collected in Paraguay, and more recently in Corrientes, Argentina. Herbaria material was analysed, but no previously existing specimens of this species from Argentina were found. Currently, O. salzmannii (DC.) Benth. & Hook. f. ex B.D. Jacks, which is native and widespread in South America and introduced in North America (i.e. Florida; ^{Fosberg &Terrell, 1985}), is the only species in the genus recorded for Paraguay and Argentina (IBODA, 2021).

The aim of this work is to shed light on these new records of O. corymbosa in Paraguay and Argentina. A detailed description and a distribution map of this species are provided, as well as, comments on its distribution and ecology. A photographic illustration to facilitate identification of this species is also provided, with a taxonomic key to distinguish it from O. salzmannii.

Material and Methods

During floristic surveys in South Paraguay and Northeast Argentina, standard taxonomic methods have been followed for the collection, drying, and processing of herbarium specimens. The specimens have been deposited in CTES and FCQ herbaria (Thiers, 2021.) Relevant taxonomic literature (Terrell & Robinson, 2006; ^{Delprete et al., 2005}), and online databases such as the Reflora Virtual Herbarium (http://reflora.jbrj.gov.br/reflora/ herbarioVirtual), speciesLink (http://www.splink. cria.org.br) and TROPICOS (https://www.tropicos.org/home), were consulted for the identification of specimens and reference. The specimens were also compared with original descriptions (Linnaeus, 1753) of Oldenlandia corymbosa, and analyzed under a (SM) Leica MZ6 stereo microscope. Measurements were made using a digital caliper, and ImageJ (Rasband, 2020).

Results and Discussion

The characters of specimens found in Paraguay and Argentina (Figs. 1-2) are in complete concordance with the description offered by Terrell & Robinson (2006) and ^{Delprete et al. (2005}), and herbaria specimens. Description presented here is based on Paraguayan and Argentinian specimens to facilitate later identifications.

Oldenlandia corymbosa L., Sp. Pl. 1: 119. 1753. Hedyotis corymbosa (L.) Lam., Tabl. Encycl. 1: 272. 1792. Gerontogea corymbosa Cham. & Schltdl., Linnaea 4(2): 154. 1829. Hedyotis biflora var. corymbosa (L.) Kurz., J. Asiat. Soc. Bengal 46(2): 133. 1877. TYPE. Plumier, Nov. Pl. Amer. 42, t. 36. 1703; lectotype designated by Verdcourt, in Polhill, Fl. Trop. E. Africa, Rubiaceae 1: 308. 1976Herbs, erect, postrate, or rarely decumbent, 6.5-15 cm tall. Stems tetragonal, 0.2-0.9 mm diam, glabrous or hirsute. Stipular sheaths free portion subtriangular, 0.7-1.7 mm long., glabrous or hirsute, with 3-5 fimbriae, unequal, 0.5-1.5 mm long, glabrous, colleter-tipped. Leaves sessile or pseudopetiolate, blades elliptic or narrowly elliptic, linear or oblong, 6.4-15.9 x 1.2-3.3 mm, acute at apex, cuneate at base, glabrous. Inflorescences cymose, 2-5-flowered, pedunculate, axillar, with small bracts ca. 1 mm long. Flowers homostylous, pedicellate, with floral pedicels 1-4 mm long. Hypanthia obconic or globose, 0.8-1.7 mm long, glabrous. Calyces 4-lobed, 0.3-1 mm long, calyx lobes ovate-triangular, erect, with serrate margins, glabrous. Corollas infundibuliform, 1.2-2.5 mm long, white, pale pink or light lilac; corolla lobes triangular-lanceolate, externally glabrous, internally with a ring of trichomes at the height of the flower throat. Stamens included, inserted at the base ofhe corolla tube; anthers oblong, 0.2-0.5 mm long. Styles included, filiform, shortly bifid, 0.1-0.3 mm long. Nectariferous disks elliptic, bipartite. Capsules subglobose, loculicidal, 1.5-1.9 x 1.9-2.3 mm, glabrous. Seeds trigonous, 0.3-0.4 mm long, numerous, with hilum apical, punctiform, with exotesta reticulate-foveate, castaneous to brown (Fig. 1-2).

Fig. 1: Oldenlandia corymbosa. A: Habit. B: Stipular sheath. C: Flower. D: Hypanthium, calyx, and style. E: Opened corolla. F-G: Dehiscence fruit. F: Lateral view. G: Subapical view. H: Seeds. A: Nuñez Florentin & Florentín 144 (CTES). B-H: Nuñez Florentin & Salas 165 (CTES). Drawn by Laura Simón, sketches of the reproductive characters by the author. 

Fig. 2: Oldenlandia corymbosa. A: Habit. B: A flowered branch. C: Flower. D: Portion of branch with immature fruits. Scales= A: 1 cm; B, D: 5 mm; C: 1 mm. Paraguay, Dpto. Central, Lambaré. 

Distribution and habitat. Oldenladia corymbosa is native in the African Continent (e.g. Nigeria, Uganda, and Kenya) and India (^{Lewis, 1964}; ^{Halford, 1992}), but currently presenting a pantropical distribution, being naturalized in The Americas and in other parts of the world. For example, in the past decade it has been cited as an alien species for the European flora in Spain (Sánchez Rodríguez et al., 2007); and in the United Arab Emirates flora, specifically in three different areas of Dubai (Shahid & Rao, 2014), in which the species is reported as an weed but with minor impact, probably not representing a big threat to the environment.

Oldenlandia corymbosa grows in open areas on sandy soils, open banks along streams, savannas, waste ground and disturbed areas, or usually on man-made environments, on rocky outcrops or between cracks on the sidewalks. Its presence in the Southern Cone of South America is reported here for the first time, growing in Paraguay and Argentina (Fig. 3). In the latter, it was only recorded in the Corrientes province, where it was observed and collected in urban and anthropized areas, growing spontaneously. It is likely that other populations f O. corymbosa could be found in similar areas to the northeast of Argentina (probably Formosa and Chaco provinces). This species could be considered as “casual alien plant” according to Pysek et al. (2004), based on its subspontaneous growing and single record. However, in Paraguay, because all individuals analysed are from the last two decades, I can consider O. corymbosa as naturalized in Paraguay (Pysek et al., 2004).

Fig. 3: Oldenlandia corymbosa. Geographic record of collected specimens in Paraguay and Argentina (red circles). Abbreviations= Arg: Argentina; Bol: Bolivia; Bra: Brazil; Par: Paraguay; Uru: Uruguay. 

Specimens examined: ARGENTINA. Prov. Corrientes: Dpto Capital, 10-X-2021, Nuñez Florentin & Salas 165 (CTES). PARAGUAY. Dpto Amambay: Bella Vista, 22° 6’ 50’’ S, 56° 31’ 4’’ W, 11-111-2018, De Madrignac Bonzi & Florentin 776 (CTES). Dpto. Central: Areguá, Lago Ypacaraí, 25° 19’ 32’’ S, 57° 23’ 55’’ W, 4-111-2018, De Madrignac Bonzi & Florentin 624 (CTES); Asunción, 25° 17’ 32’’ S, 57° 37’ 44’’ W, X-2014, Mereles 1012(FCQ); idem, X-2014, Mereles 10120 (FCQ); Lambaré, Cerro Lambaré, 5-VIII-2015, Nuñez Florentin & Florentín 144 (CTES); San Lorenzo, 25-XI-2016, Martinez et al. 193 (CTES, FCQ).

Key to species of Oldenlandia in Argentina and Paraguay

1. Herbs erect or póstrate. Inflorescences cymose, 2-5-flowered, axillary. Flowers homostylous with corollas 1.2-2.5 mm long, internally with a ring of trichomes at the height of the flower throat.

O. corymbosa

1'. Herbs creeping, radicant at the nodes. Inflorescences cymose, 1-3-flowered, terminal and pseudoaxillary. Flowers heterostylous with corollas 4-8 mm long, internally with a fringe of trichomes on the tube or a ring of trichomes at the throat. O. salzmannii

Conclusions

With the addition of O. corymbosa, the genus Oldenlandia is now represented by two species in Paraguay and Argentina. Oldenlandia corymbosa can be differentiated from O. salzmannii on the basis of general habit and floral characters, such as floral biology, corolla length, and internal indumentum.

I agree with previous authors that this species does not present a potentially invasive behavior. However, its occurrence should be reported for Paraguay and Argentina as a means to complement these countries floras. Its naturalized status in Northeast and South Paraguay raises the possibility that it was, until now, overlooked in places like the Formosa and Chaco Provinces (Northeast Argentina), or even in other regions of Paraguay.

Acknowledgements

The author thanks the Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET) for the grants awarded that supported this work (PICT-2016-3517). This work was also partially funded by the Universidad Nacional del Nordeste (PI A009-17 and PI 16P001 grants).

I am grateful to the staffs of FCQ and FCYN herbaria, especially Maria Vera and Christian Vogt. Also, Roberto M. Salas, Mariana Martinez, Javier E. Florentín, Laila M. Miguel and Marina D. Judkevich for their assistance in the field trip to Paraguay, and Laura Simón for the line drawings.