Ludwigia irregularis Funez, Hassemer, D.M. Farias & Gasper, 2021

Funez, Luís Adriano, Farias, David Moura, Gasper, André Luís De & Hassemer, Gustavo, 2021, Ludwigia irregularis (Onagraceae) a rare new species from southern Brazil, and typification of the morphologically similar L. myrtifolia, Phytotaxa 520 (3), pp. 257-264 : 258-262

Ludwigia irregularis Funez, Hassemer, D.M. Farias & Gasper , sp. nov. Figures 1 , 2 .

Type: — BRAZIL. Santa Catarina: Ascurra, Nova Brasília , 12 January 2020, L. A . Funez 9617 (holotype FURB!; isotypes HBR!, HTL!)

Diagnosis: — Ludwigia irregularis is similar to L. myrtifolia , differing from it by its leaves elliptic-lanceolate, attenuate at base, flowers with 4–5(–6) floral segments, ovary long obconic and seeds pilose (vs. erect habit, leaves lanceolate, truncate to subcordate ate base, flowers with 4 floral segments, ovary obpyramidal and seeds smooth in L. myrtifolia ).

Description: —Subshrubs to shrubs, perennial, 0.5–1.50 m tall, erect, decumbent or prostrate. Stems subquadrangular, green to brown, pubescent, long, scandent, rarely rooting. Stipules deltoid, deciduous, green, 0.1–0.3 × 0.1–0.2 mm, the apex acute. Leaves subsessile, petioles 0.5–2.0 mm long, densely pilose. Blades entire, papyraceous, adpressed shortpilose adaxially and densely hispid along the main and secondary veins abaxially, 14–51 × 5–10 mm, elliptic to elliptic lanceolate, ciliate along margin, long cuneate at base, decurrent to petiole, acute at apex, with 9–11 veins on each side of midvein, prominent on the abaxial surface, tertiary veins inconspicuous, submarginal vein very inconspicuous, visible at the abaxial surface, 0.1–0.2 mm from the margin. Bracts similar to other leaves. Pedicels 3–14 × 0.5 mm, densely pubescent. Flowers solitary, axillary. Bracteoles 2, borne at the base of ovary, occasionally deciduous, papyraceous, green, 2–3 × 0.1–0.3 mm, subulate, apex acute, subtended by a pair of persistent deltoid stipels ca. 0.1 × 0.1 mm. Sepals 4–5(–6), deltoid to lanceolate, acute at tip, green, densely pubescent on the abaxial surface, 7–12 × 2–3 mm, venation inconspicuous. Petals 4–5(–6), yellow, obovate, acute or slightly unguiculate at base, obtuse to slightly emarginate at the apex, 13.5–17.0 × 10–14 mm. Stamens 8–10, unequal, the episepalous longer, with filaments 0.4–0.5 mm long and anthers 1.6–2.0 × 0.5 mm, oblong, curved; epipetalous with filaments 0.2–0.4 mm long and anthers 1.3–1.4 × 0.4 mm. Ovary long obconic, strongly 4-angled, puberulent, 6–10 × 2.0– 2.5 mm. Disk elevated, 0.7–1.0 mm high, with a line of pubescent trichomes at the insertion of each stamen; style 1.0– 1.3 mm long, stigma subglobose, conspicuously 4–5 lobed, 1 × 1.6–1.8 mm. Capsules long obconic, 4-angulose, villose, 13–20 × 3–4 mm at maturity. Seeds numerous, pluriseriate in each locule, brown, longitudinally striated, testa covered by numerous curly hairs along the striations, 0.7–0.8 × 0.3–0.4 mm, rafe not conspicuous, <1/5 of the length of the seed.

Etymology: —The specific epithet is a reference to the irregular number of petals, an uncommon characteristic for Ludwigia , specially in section Myrtocarpus , in which all other species have four petals.

Distribution and habitat: —The new species is known from three localities in the South Region of Brazil: in Ascurra municipality, Santa Catarina state, Capivari do Sul and Pântano Grande municipalities, in Rio Grande do Sul state. The species occurs in open and swampy environments, under a certain anthropic impact. This species is probably naturally rare and sparsely-distributed along with open swampy areas in the Atlantic Forest and Pampas biomes in southern Brazil ( Figure 2 ).

Conservation status: — Critically endangered ( EN — B2 a,b[iii]). Ludwigia irregularis has a confirmed area of occupancy ( AOO) of less than 12 km 2, with only three disjunct populations known. Both populations are located out of any environmentally protected area, and the population from Ascurra municipality was destroyed due to housing development, after the type was collected .

Notes: —The new species belongs to Ludwigia section Myrtocarpus due to its woody stems, perennial habit, obconic 4-angulose capsules, four petals, and seeds pluriseriate in each locule with inconspicuous rafe. The characteristic of more than four petals is an interesting novelty for the section Myrtocarpus , as the winged stems in Ludwigia humboldtiana Funez, D.M.Farias, Hassemer & Gasper (2020: 80) , showing that the section Myrtocarpus is more morphologically rich than were previously supposed to be. The presence of flowers with four and five floral parts in the same plant could be an indicative of an inter-sectional hybrid between a four-petaled and a five-petaled sympatric species, as Ludwiga peruviana Linnaeus (1753: 388) Hara (1953: 293) × Ludwigia leptocarpa Nuttal (1818: 279) Hara (1953: 292) for example. But, this theory does not explain the six-petaled flowers, the presence of this very specific morphology in three distinct places without some intermediary forms and the whole morphology of the plant that is within section Myrtocarpus , except the number of floral segments. Thus, we do not rule out the possibility of L. irregularis be originate by a hybridization event, but the evidence we have collected does not allow us to confirm this hypothesis.

Ludwigia irregularis is similar to L. irwinii Ramamoorthy (in Ramamoorthy & Zardini 1987: 66), L. martii ( Micheli 1875: 300) Ramamoorthy (in Ramamoorthy & Zardini 1987: 64) and L. myrtifolia . All these species are morphologically narrowly related, being considerably similar among them. These species can be differentiated from L. irregularis due the following set of characters: base of leaf blades acute, truncate or subcordate, not attenuate, filaments> 1 mm long, ovary and capsules obpyramidal and flowers regularly tetramerous vs. base of the leaf blades attenuate, filaments up to 0.5 mm long, ovary and capsules long-obconic and flowers regularly 4–5 (rarely–6)-merous on the same plant in L. irregularis ). Additional characters that distinguish L. irregularis from each of the above-mentioned species are listed in Table 1.

Ludwigia irwinii has two disjunct populations, one in Southeast region Brazil, in Minas Gerais, São Paulo, and Rio de Janeiro states, and one in Argentina, in Misiones and Corrientes provinces, reaching eastern Paraguay. Ludwigia martii is more widely distributed in Brazil, Paraguay, and Argentina ( Ramamoorthy & Zardini 1987). In Brazil, this species occurs in Mato Grosso, Mato Grosso do Sul, Goiás, Minas Gerais, São Paulo, Rio de Janeiro, Paraná, Santa Catarina, and Rio Grande do Sul states ( Ramamoorthy & Zardini 1987, Pesamosca 2015, Zeferino 2020).

myrtifolia .

According to Ramamoorthy & Zardini (1987) and Zeferino (2020), Ludwigia myrtifolia occurs only in Minas Gerais state. Additionally, Pesamosca (2015) indicates that this species occurs in Paraná state. Analyzing herbarium samples, besides Minas Gerais and Paraná, we observed samples from São Paulo and Mato Grosso do Sul states that match with the morphology of L. myrtifolia . Although Pesamosca (2015) cites L. myrtifolia as a species that occurs in Rio Grande do Sul state, all the exsiccates that we examined were misidentifications, corresponding to Ludwigia irregularis (see paratypes), Ludwigia multinervia ( Hooker & Arnott 1833: 312–313) Ramamoorthy (in Ramamoorthy & Zardini 1987: 40), and L. peruviana or L. caparosa ( Cambessèdes 1829: 258) Hara (1953: 292) . We could not identify precisely this specimen based solely on the examination of its image (see below).

Specimen examined of Ludwigia caparosa or Ludwigia peruviana :— BRAZIL. Rio Grande do Sul, 1833, C. Gaudichaud 1276 (P-05183229, image!).

Specimen examined of Ludwigia multinervia :— BRAZIL. Rio Grande do Sul: Barra do Ribeiro, Área da Riocell , 26 April 2002, R. A. G.Viani et al. s.n. (ESA-94674, image!) .

Paratypes: — BRAZIL. Rio Grande do Sul: Pântano Grande , 13 January 2015, P. J. S . Silva-Filho et al. 2215 (ICN-181057!); Capivari do Sul, RS-040, 6 December 2013, S. C . Pesamosca & M. G . Facco 275 (FLOR-60926!, ICN-180836!, PACA-AGP-115769, PEL, HUCS) .

Figures

FIGURE 1. Field photographs of Ludwigia irregularis. A. Flower with five petals. B. Flower with four petals. C. Leaf blade (abaxial surface). D. Leaf blade (adaxial surface). E. Immature fruit, showing the bracteoles near the apex of pedicel. F. Habit.

FIGURE 2. Distribution map of Ludwigia irregularis.