Argythamnia estacionalis Ornelas & Külkamp, 2024

Ornelas, Márcia Martins, Külkamp, Josimar, Santos, Francisco De Assis Ribeiro Dos & Carneiro-Torres, Daniela Santos, 2024, New species of Argythamnia (Euphorbiaceae) restricted to Seasonal Forest of Brazil, with morphological and phylogenetic support, Phytotaxa 649 (2), pp. 211-222 : 216-220

Argythamnia estacionalis Ornelas & Külkamp , sp. nov. Figs. 4 , 5 .

Type:— BRAZIL. Bahia: Itaju da Colônia , 7.5 km a sudeste da cidade, na rodovia para Palmira, 19 March 2001, W. W. Thomas 12361 (holotype CEPEC00088126 !; isotypes NY00642545 !, MO3127828 !, SP364483 !) .

Diagnosis: — Argythamnia estacionalis differs from other species of the genus by an entire, rarely serrated leaf margin; unisexual inflorescences; presence of an anthophore in the staminate flowers, and glabrescent staminodes. Argythamnia estacionalis is similar to A. simoniana and A. desertorum , but these differ by a serrated leaf margin; inflorescence only bisexual in A. simoniana and unisexual or bisexual in A. desertorum ; an anthophore being absent in the staminate flowers, and pubescent staminodes.

Description: —Shrubs 1–1.5 m tall, monoecious; stems branched, erect, with malpighiaceous trichomes on young branches; latex absent. Stipules 2.4–2.6 mm long, lanceolate, persistent. Leaves simple, alternate; petiole 1.8– 4.4 mm long, pubescent with malpighiaceous trichomes; blade 28.7–92.9 × 10.2–29.4 mm, lanceolate, elliptic to obovate, membranous; base acute to cuneate; apex acute to mucronate; margin entire or, rarely serrated with 3–6 teeth; nerves acrodromous; adaxial surface glabrous to glabrescent with trichomes restricted to central vein, abaxial surface pubescent. Inflorescences axillary, staminate ones racemoid, 8.8–16.2 mm long, with 3–5 flowers; pistillate flowers solitary. Staminate flowers 5.3–6.2 mm diam., dichlamydeous, actinomorphic; pedicel 1.9–2.1 mm long; sepals 5, 3.2–3.5 × 1.8–2.2 mm, lanceolate to elliptical, margin entire, free, valvate in bud, adaxial surface pubescent, abaxial surface sparse-pubescent to glabrous, green; petals 5, 3.3–3.6 × 1.8–2 mm, obovate, margin entire, free, valvate in bud, adaxial surface pubescent, abaxial surface glabrous, white; anthophore 0.8–0.9 mm long; stamens 10 (5 + 5) in 2 whorls, filaments fused forming a column 2.3–2.6 mm long, yellow; staminodes 5, apical, glabrescent; nectaries 5, glabrous, adnate at the base of the staminal column. Pistillate flowers 9.8–13.5 mm diam., dichlamydeous, actinomorphic; pedicel 4.6–6.7 mm long; sepals 5, 7.8–8.7 × 2.6–3.3 mm, lanceolate to elliptic, margin entire, free, pubescent on both surfaces, green; petals 5.5–6 × 1–1.2 mm, lanceolate, margin entire, free, pubescent on both surfaces, white; nectaries 5, glabrous; ovary 2.3–2.5 mm long, superior, tricarpellate, pubescent; styles 3, bifid, pubescent to glabrescent. Capsule 6.7–9.8 mm diam., pubescent, green, persistent sepals. Seeds 3.6–4 mm diam., globose, smooth, gray, caruncle absent.

Paratypes: — BRAZIL. Bahia: Itaju da Colônia, 12 Km da estrada em direção a Feirinha , a W. da margem esquerda do Rio Corró , 23 October (fl.), T. S. dos Santos 427 ( CEPEC 5256 ) ; T. S. dos Santos 437 ( CEPEC 5243 , RB 84603 ) ; Trajeto entre Itaju da Colônia e Santa Cruz da Vitória , 17 Km de estrada, 02 October 1969 (fl.), T. S. dos Santos 398 ( CEPEC5346 ) ; 8.4 km de Santa Cruz da Vitória em direção a Itaju do Colônia , 15°01’52’’S, 39°47’38’’W, 26 June 2022 (buds), M. M. Ornelas et al. 65 ( HUEFS, EAC) ; 8.4 km de Santa Cruz da Vitória em direção a Itaju da Colônia. 50 metros em estrada secundária à esquerda do sentido do trajeto, 15°01’52’’S, 39°47’38’’W, 26 June 2022 (fl.), J. Külkamp et al. 1568 ( HUEFS, ICN, MA, RB). Itambé, Rodovia BA-265, km 8 do trecho BR-415 (cruzamento)/ Caatiba e a 15 km NW de Itapetinga em linha reta, próximo a Fazenda São João , região de mata mesófila sul baiana, 03 March 1978 (fr.), S. A. Mori et al. 9386 ( CEPEC) ; 18.6 km de Itambé para Itapetinga , mata na margem da BR-415, 15°16’48”S, 40°27’38W ”, 26 June 2022 (buds), M. M. Ornelas et al. 57 ( CEPEC, HUEFS); 18.6 km de Itambé para Itapetinga, mata na margem da BR-415, 15°16’48”S, 40°27’38W ”, 26 June 2022 (buds), M. M. Ornelas et al. 58 ( HUEFS, HST, IPA) ; 18.6 km de Itambé para Itapetinga , mata na margem da BR-415, 15°16’48”S, 40°27’38W ”, 26 June 2022 (fl.), M. M. Ornelas et al. 59 ( HUEFS, MAC, CEPEC, ALCB); 18.6 km de Itambé para Itapetinga, mata na margem da BR-415, 15°16’48”S, 40°27’38W ”, 26 June 2022 (buds), M. M. Ornelas et al. 60 ( HUEFS, HUESB) ; Mata na margem da BR 415 , 15°16’48’’S, 40°27’38’’W, 26 June 2022 (fl.), J. Külkamp et al. 1562 ( HUEFS, ICN, MA, RB) ; J. Külkamp et al. 1563 ( FLOR, HUEFS, ICN, MA, RB). Minas Gerais: Salto da Divisa, 7 km E. de Salto da Divisa na estrada em direção a BR-101, dobra ao sul entrando na Fazenda Ensoado e segue até um remanescente de mata antes do mata-burro, 15°52’20’’S, 39°31’40’’W, 28 March 2009 (fl.), D. Cardoso et al. 2431 ( HUEFS) .

Etymology: —The specific epithet “ estacionalis” refers to the vegetation formation Seasonal Forest (Floresta Estacional), to which A. estacionalis is endemic.

Distribution and habitat: —The species is endemic to Seasonal Forest fragments in the southern state of Bahia and northeastern Minas Gerais (MG) ( Fig. 6 ). We emphasize that the collection of Minas Gerais (Salto da Divisa city) is 900 meters away from the border of the state of Bahia and approximately 100 km in a straight line from the nearest known record. Only 14 records of A. estacionalis are known, distributed in only six nearby locations, totaling an occurrence extension of 5,504 km 2 ( Fig. 6 ). The populations observed during the field expeditions (from Santa Cruz da Vitória to Itaju do Colônia; Itambé to Itapetinga; Itajú from Colônia to Jussari, all in the state of Bahia) occurred in seasonal forest, highly fragmented and with cattle raising. Populations were observed in the interior and edge of the forest ( Fig. 5A ). During the field activity, residents of the region reported that the fragmentation of vegetation is historical, initially for cocoa cultivation and later for cattle raising. The observed populations co-occurred with other Euphorbiaceae species such as Philyra brasiliensis Klotzsch (1841: 199) , Adelia membranifolia ( Müller 1874: 306) Chodat & Hassler (1905: 604) , and Actinostemon Martius ex Klotzsch (1841: 184) .

Phenology: —Flowering records are from March to October and fruiting in March. This period coincides with the end of the dry season and the beginning of the rainy season. We believe that a greater collection effort may show a longer fruiting and flowering period.

Preliminary conservation assessment: — Argythamnia estacionalis is known from 14 records corresponding to six different localities. The records correspond to an AOO of 24 km 2 and EOO of 5.504 km 2. Based on geographic distribution data and analysis of field populations, here we preliminarily assess the species as Endangered (EN B2b (i,ii,iii)). The main threats incident on the subpopulations are the severe fragmentation of the environment due to the conversion of areas to monoculture and cattle ranching, the observed continuous decline of AOO and EOO and the loss of habitat quality in their distribution.

Notes: —Previous authors identified specimens collected in southern Bahia and northeastern Minas Gerais as A. simoniana . These records point to a great geographical disjunction for A. simoniana , which is endemic to the coast of the state of Rio de Janeiro.

According to Külkamp (2022), geographical disjunction within the same species is rare in Argythamnia , being recorded only in northern South America and the Caribbean islands (e.g. A. argothamnoides (Bertero ex Sprengel 1826: 872) Ingram (1953: 423) , A. candicans Swartz (1788: 39) , and A. fasciculata ). Another specimen collected in Bahia was determined as A. simoniana (Blanchet 2901 [K, P]), but during the study by Külkamp et al. (2020), it was verified that this specimen is A. malpighiacea .

Molecular and morphological studies and field expeditions were essential to confirm that the records from southern Bahia and northeastern Minas Gerais, identified as A. simoniana , corresponded to the new species.

Comparisons of sequence variation based on the four regions show that A. estacionalis is genetically distinct from closely related taxa, reinforcing its classification as a separate species. Argythamnia estacionalis is morphologically close to A. desertorum , however, the molecular data point to a significant genetic distance with this geographically closer species ( Fig. 1 ). Argythamnia simoniana is phylogenetically close to A. estacionalis , however, morphological differences are more expressive when compared with A. desertorum .

Palynological studies have been used to support the generic classification of Euphorbiaceae , helping the taxonomy ( Webster 2014). Souza et al. (2017) point out that the species of Acalyphoideae present pollen variations, with the types of aperture and ornamentation of the exine being important diagnostic characters. According to Souza et al. (2017), in Acalyphoideae the pollen grains are monads, with sizes ranging from medium to large, isopolar, shapes ranging from suboblate to subprolate, subcircular, with circular and subtriangular amb, small, very small or large polar area, 3(–4)-colporate to 3-colpate, presence of a granulated to echinate-granulated membrane at the aperture, elongated endoaperture; exine varying from microreticulate, reticulate, bireticulate or microequinate-perforated and sexine thicker than nexine. According to these authors, it is a subfamily with no apparent differences between its species, a stenopalynous taxon.

Nowicke et al. (1999) pointed out the pollen grains of Argythamnia as being tetracolpate and those of Ditaxis as tricolpate, both genera with pollen grains that are never operculate. Despite small differences, Croizat (1945) did not agree with the separation of Ditaxis and Argythamnia based in pollen morphology. Punt (1962) analyzed the pollen grains of A. candicans which showed similarities with the pollen type of Ditaxis and therefore was included in this pollen type. Webster (2014) points out that the pollen grains of Argythamnia are 4-colporate, with inoperculate colpi and a tectate-perforate sexine, while Ditaxis has oblate, asymmetrically 3-colporate grains with inoperculate colpi and a tectate-punctate (superreticulate) sexine. The pollen morphology of the species analyzed here corroborates previous studies, since they do not present a clear pattern that delimits Ditaxis and Argythamnia . With the recent phylogeny of Külkamp et al. (2023), the taxonomic combination between the genera highlights the importance of further studies.

Figures

FIGURE 1. Phylogenetic reconstruction presenting the positioning of Argythamnia estacionalis in relation to the other species of the genus.

FIGURE 4. Argythamnia estacionalis. A. Flowering branch; B. Adaxial surface of the leaf; C. Detail of adaxial surface of the leaf glabrescent; D. Abaxial surface of the leaf; E. Leaf pubescence on the abaxial surface; F. Pistillate specimen; G. Staminate specimen; H. Staminate flower; I. Anthophore (sepals and petals removed for image capture); J. Pistillate flower. (A, H, I. W.W. Thomas 12361 (CEPEC); B–F, J. M.M. Ornelas 59 (HUEFS); G. M.M. Ornelas 65 (HUEFS)). Illustration by Marilane Luz.

FIGURE 5. Habitat and morphological characteristics of Argythamnia estacionalis. A. Fragment of Seasonally Dry Tropical Forest and Woodlands (SDTFW) in Itambé, Bahia, Brazil; B. Habit of Argythamnia estacionalis; C. Adaxial surface of the leaf; D. Abaxial surface of the leaf; E. Staminate specimen; F. Pistillate specimen. Figure assembled by Márcia M. Ornelas. Voucher specimens: C, D, F, M.M. Ornelas 59 (HUEFS); E. M.M. Ornelas 66 (HUEFS).

FIGURE 6. Geographic distribution of Argythamnia estacionalis in southern Bahia and northeastern Minas Gerais, Brazil.