Dimerostemma pantanalense D.M.Mendes & A.M.Teles

Mendes, Daniel De Menezes, Dorneles Welker, Cassiano A., Farinaccio, Maria Ana & Teles, Aristônio Magalhães, 2024, Contributing to the knowledge of Pantanal Flora: a new endemic species of Dimerostemma (Asteraceae: Heliantheae) from Mato Grosso do Sul, Brazil, Phytotaxa 659 (3), pp. 277-285 : 278-283

Dimerostemma pantanalense D.M.Mendes & A.M.Teles , sp. nov. ( Figs. 1−4 )

The new species is morphologically similar to Dimerostemma annuum ( Hassler 1915: 175) Robinson (1984b: 621) but differs mainly in its perennial (vs. annual) life-cycle, lanceolate (vs. linear) leaf blades, suprabasal acrodromous imperfect (vs. hyphodromous) venation, strongly villous to strigose and glandular leaf indumentum (vs. leaves nearly glabrous), convex to conical (vs. convex) receptacle, and carinate-alate (vs. not carinate-alate) palea.

Type: — BRAZIL. Mato Grosso do Sul: Ladário, Assentamento 72, Pantanal , 19º02′41″S, 57º34′39″W, 130 m, 9 January 2023, D. M. Mendes, P. M. Mendes & R. F. Mendes 72 ( holotype: COR, barcode COR00031524 !; isotypes: ALCB!, HUFU!, RB!, SPF!, UFG!) .

Herbs perennial, 1.0− 1.5 m tall. Stem and branches erect or prostrate, slender, cylindrical, hairy, villous. Leaves simple, opposite, and decussate, alternate, and spirally situated on the main branches where the capitula emerge, sessile; leaf blade lanceolate, 3.3−5.6 × 0.6−1 cm, base cuneate, margins entire to slightly crenate, plane, apex acute, venation suprabasal acrodromous imperfect, adaxial and abaxial surfaces ranging from slightly to strongly villous at the base of the blade, becoming strigose towards the leaf apex, and glandular. Capitulescence corymbiform. Capitula heterogamous, radiate, pedunculate; peduncle 8−20 cm long, villous; involucre campanulate, 1.0−2.0 × 1.3−2.5 cm; phyllaries 3-seriate, decreasing in size from the outer series to the inner ones, outer phyllaries narrow-lanceolate, 3.5−5.0 × 0.7–0.9 cm, foliaceus, apex acute, base cuneate, villous; middle phyllaries oval-lanceolate, 0.7−3.2 × 0.5–0.7 cm, foliaceus, apex acuminate, base cuneate, villous; inner phyllaries oval-lanceolate, 8−10 × 1.5–2.5 mm, foliaceus or scarious with distal portion foliaceus, apex acuminate, base cuneate, villous; receptacle convex to conical, paleaceous, paleae conduplicate, carinate-alate, 3.0−5.0 mm long, apex acuminate. Ray florets 10–40, sterile (with pistillode), corolla liguliform, yellow, tube ca. 3 mm long, lamina oblong to elliptic or narrow-obovate, 1.0−2.0 × 0.3−0.5 cm. Disc florets more than 100 per capitulum, bisexual, corolla tubulose, actinomorphic, 4.0− 4.5 mm long, lobes 5, yellowish, papillate adaxially, tube 2.8−3.1 mm long, corolla limb ca. 1 mm long, lobes ca. 0.5 mm long, sparsely pubescent, and usually sparsely setulose abaxially, presenting glandular trichomes at the base; anther thecae 1.9−2.1 mm long, blackish; style 2.4−2.5 mm long, yellowish, style branches protruding, ca. 1 mm long, strongly coiled after anthesis, often glandular-punctate abaxially, apically pilose, appendages short, acute to acuminate, ending with trichomes. Cypselae oblanceolate to obovate, 2-winged, wings continuous or lacerated 0.8−1 mm long, body surface tuberculate, 2–3 mm long, brown or blackened. Pappus 0.1−0.3 mm long, coroniform with two slightly developed awns, persistent.

Paratypes: — BRAZIL. Mato Grosso do Sul: Corumbá, Bairro Universitário, atrás do CPAN / UFMS Unidade I, 18º59′59″S, 57º37′48″W, 125 m, 29 January 1998, L. B. Costa, I. Carvalho, R. Alvarenga & H. Rodrigues 81 ( COR, HUFU) ; Ladário , Alta Floresta II, 19º1′17″S, 57º35′5″W, 100 m, 26 July 2023, D. M. Mendes & R. F. Mendes 127 ( COR, HUFU) ; APA Baía Negra , trilha base UFGD, 19º1′27″S, 57º34′34″W, 130 m, 1 February 2023, D. M. Mendes, R. G. Silva, M. V. S. Urquiza & M. S. Lima 90 ( COR, HUFU) ; Assentamento 72, 24 February 2012, P. P. Oliveira, M. V. S. Urquiza, M. Diamante & M. E. C. Campos 68 ( COR) ; Estrada para a Codrasa , 19º03′10″S, 57º34′36″W, 28 November 2000, M. D. Moraes & G. Damasceno Junior 546 ( UEC) ; Mangueiral , 19º0′56″S, 57º35′59″W, 137 m, 13 February 2012, A. Pott & V. J. Pott 16331 ( CGMS) ; Rodovia Corumbá— Ladário, Bifurcação para a Codrasa , Pantanal , 19º01′36″S, 57º35′47″W, 144 m, 30 June 2013, M. Monge, C. Delfin & J. Rigon 1940 ( UEC, ESA) .

Distribution and ecology: — Dimerostemma pantanalense is distributed in the municipalities of Ladário and Corumbá, Mato Grosso do Sul state, within the phytogeographic domain of the Brazilian Pantanal, in fragments of vegetation in the urban zone. In Ladário, the materials D.M. Mendes et al. 72, D.M. Mendes & R.F. Mendes 127, D.M. Mendes et al. 90, P.P. Oliveira et al. 68, M.D. Moraes & G. Damasceno Junior 546, A. Pott & V.J. Pott 16331 and M. Monge et al. 1940 were collected in anthropic areas. Furthermore, only one specimen was found in the city of Corumbá (L.B. Costa, et al. 81), almost 30 years ago. All examined materials were collected in herbaceous-shrub secondary vegetation in the semideciduous seasonal forest, with shallow clayey soil and limestone outcrops, and a flat relief.

Phenology: — Dimerostemma pantanalense was collected with floral buds, flowers, and fruits in January, February, June, July, and November.

Etymology: —The specific epithet is a term from Tupi-Guarani (an Indigenous language) and honors the Pantanal biome, referring to the marsh due to its floodplain nature. Additionally, it also refers to the restricted distribution of the species, which is microendemic to the municipalities of Ladário and Corumbá and strongly influenced by the Brazilian Pantanal.

Preliminary conservation status: —The new species is currently represented by small and isolated populations in the municipality of Ladário, Mato Grosso do Sul state. The highest population density is found in the Alta Floresta II neighborhood, with over 50 individuals, while fewer than 10 individuals are found in other locations. The risk of extinction is imminent, particularly due to urbanization, as most specimens are in vegetated areas within the urban zone, similar to what occurred in the municipality of Corumbá. Despite the high collection effort, this species was not found in the area, with only one record dating back to 1998. Another risk factor is the occurrence of fires in the Pantanal. While fires in the Pantanal are less frequent and more localized compared to the drier vegetation, such as the savannas of the Cerrado, there is an anticipated intensification of fire risk ( Thielen et al. 2021). This will undoubtedly have a severe impact on vegetation that is not fire-resistant, endangering the flora of the Pantanal. Only specimens in the APA Baía Negra are protected by a Conservation Unit, despite this, these APAs are not fully protected conservation units and are often ineffective because they allow too many human activities to take place in their areas. As a result, these sites are heavily altered by human activities, as is the case with the APA Baía Negra. The GeoCAT tool (GeoCAT 2024) shows that the extent of occurrence (EOO) is 9.1 km 2, and the area of occupancy (AOO) is 20 km 2. Additionally, following the IUCN Red List ( IUCN Standards and Petitions Committee 2024) guidelines, the species is categorized as Critically Endangered (CR), Criterion B1ab (i, ii, iii, iv).

Taxonomic comments: — Dimerostemma pantanalense is morphologically similar to D. annuum , mainly due to their herbaceous growth and the arrangement of their capitula. However, it differs from the latter in several characters, such as life-cycle duration, phyllotaxy, leaf attachment, indumentum and shape, venation type, receptacle, phyllaries series, palea, cypsela and pappus shape, as summarized in Table 1 . The new species can be differentiated from other species of the genus occurring in the Pantanal by the taxonomic identification key provided as follows.

Figures

FIGURE 1. Dimerostemma pantanalense. A. Flowering branch. B. Abaxial surface of the leaf showing the suprabasal acrodromous imperfect venation. C. Leaf detail showing the indumentum. D. Front view of the radiate capitulum. E. Radiate capitulum in longitudinal section, showing the convex receptacle. F. Receptacle in longitudinal section showing the conical shape. G. Phyllary from the first series of involucre. H. Phyllary from the second series of involucre. I. Phyllary form the third series of involucre. J. Palea. K. Disc floret and immature cypsela. L. Anther in ventral view. M. Anther in dorsal view. N. Style. O. Ray floret. P. Inner cypsela. Q. Outer cypsela. All from the holotype (COR). Drawn by Klei Sousa.

FIGURE 2. Field photographs of Dimerostemma pantanalense. A–B. Front view of the radiate capitulum. C. Details of the involucre. D. Habit. E. Population in the natural environment. Photos by D.M. Mendes.

FIGURE 3. Dimerostemma pantanalense. A. Inner involucral bract. B. Conical receptacle. C. Ray florets. D. Disc floret. E. Inner cypsela. F. Outer cypsela. Photos by D.M. Mendes.

FIGURE 4. Geographic distribution of Dimerostemma pantanalense.