Croton carajasensis Sodre & Secco 2023, sp. nov.
Creators: name: Sodré, Rodolfo Carneiro
name: Secco, Ricardo De S.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malpighiales
Euphorbiaceae
Croton
Croton carajasensis

description: Croton carajasensis Sodré & Secco, sp. nov. (Figures 1 and 2)
Type:— BRAZIL. Pará: Marabá, Serra dos Carajás, 23 October 1985, fl., fr., R.S. Secco & O. Cardoso 587 (holotype MG 131808!, isotypes HRCB 24175!, MBM 193965!, SPF 113489!).
Diagnosis:— Croton carajasensis Sodré & Secco shares with C. abaitensis Baillon (1864: 337), C. adamantinus Müller Argoviensis (1873: 115), C. harleyi Carn. -Torres & Cordeiro in Carneiro-Torres et al. (2011: 128) and C. ramosissimus Sodré & Silva (2017: 128) the shrubby or subshrubby habit densely ramified, the ovate, oval-lanceolate or elliptic leaf blades with slightly cordate or obtuse base, thyrses up to 4 cm long with continuous flowers, bracts longer than 2 mm, 2-fid styles, and the usually accrescent calyx in fruit. However, C. carajasensis differs from all the above-mentioned species by having alternate branching pattern; cupuliform basilaminar nectaries; staminate flowers with longer sepals, petals and stamens; obovate, oblong or elliptic unequal pistillate sepals; and globose capsules 5.5–7.5 mm in diameter (Table 1).
Shrub or subshrub 0.6–1.8 m tall, monoecious, erect, pseudomonopodial branching, with a main stem extended bearing lateral alternate branches; young branches with tomentose or glabrescent indument of multiradiate trichomes, whitish, ferrugineous or cinereous, latex not observed. Leaves alternate; stipules 2.2–2.8 × 0.25–0.3 mm, linear-lanceolate, with stellate trichomes dorsally, glabrous ventrally; petiole 0.2–1.8 cm long, tomentose, with 2 or 3 nectary glands cupuliform at the apex, 0.4–0.6 mm diam.; leaf blades chartaceous, 1.5–6.5 × 0.7–3.5 cm, ovate, oval-lanceolate, elliptic-oblong or elliptic-lanceolate, apex acute or acuminate, base obtuse or rounded, margin crenate or serrate with nectary glands cupuliform in the sinuses, visible on the abaxial face, venation brochidodromous with 4–6 pairs of secondary veins, triplinerved at the base, sometimes with stipitate-capitate glands (probably colleters) on the abaxial surface of the blade, strongly discolorous, clear-green adaxial surface and whitish abaxial surface, both tomentose with multiradiate or stellate trichomes, shortly stipitate. Thyrses 2–4 cm long, congested, terminal, bisexual, 2–4(–7) pistillate flowers at the base, followed by staminate flowers, sometimes unisexual thyrses, bracts 2–2.2 × 0.3–0.35 mm, linear, with stellate trichomes dorsally, pubescent ventrally. Staminate flowers 7–10 mm long, pedicel 2.5–4 mm long, tomentose, sepals 5, 2.5–3 × 1.2–2 mm, ovate or lanceolate, slightly unequal, pubescent dorsally, glabrous ventrally; petals 5, 3–4.5 mm long, obovate or oblanceolate, pubescent ventrally, villous dorsally; stamens (10–)11(– 12), 4.5–6 mm long, with villous trichomes, disk 5-segmented. Pistillate flowers 6–7 mm long, pedicel 1–2.5 mm long, tomentose, sepals 5, unequal, free or united at the base, the four largest ones 3.5–7 × 1.5–3 mm, obovate, oblong, elliptic, sometimes elliptic-lanceolate or oval-lanceolate, apex acute, the smallest one ca. 1.5–5 × 0.6–1.5 mm, lanceolate, apex acute, both with reniform basal gland on the ventral surface, with trichomes on dorsal surface and near the margin on ventral surface; petals absent; ovary 2.5–3 mm diam., subglobose, tomentose, disk 5-lobed, styles 3, 2-fid, 3–7 mm long, pubescent. Capsules 5.5–7.5 mm diam., subglobose, tomentose, clear-green; seeds 3.3–4.5 mm long, ellipsoid or broadly ellipsoid, surface smooth, grayish with discrete brownish spots or without spots, with discrete caruncles.
Etymology:—The specific epithet alludes to Serra dos Carajás, where the species occurs.
Distribution and habitat: — Croton carajasensis is endemic to the southwest of the state of Pará, occurring in the municipalities of Canaã dos Carajás, Curionópolis, Marabá and Parauapebas. It grows in rocky fields canga in the Serra dos Carajás, in the following Conservation Units: Carajás National Forest (Serra Sul and Serra Norte), and Campos Ferruginosos National Park (Serra do Tarzan and Serra da Bocaina), and also in the Serra Leste; between 600 and 770 m of elevation (Figure 3).
Phenology: —Flowers and fruits have been recorded throughout the year, but especially between September and February.
Preliminary conservation status: — Croton carajasensis grows in a region that has suffered in recent decades from deforestation for the establishment of mines and the expansion of agribusiness. Despite this, of the 13 locations where the species was collected, only one is not protected by a Conservation Unit. The other populations are distributed in the Carajás National Forest and in the Campos Ferruginosos National Park. Croton carajasensis is considered here as Least Concern (LC) regarding its conservation, since it grows in areas preserved and protected by law, even though it has a reduced Area of Occupation (ca. 40 km 2) and Extent of Occurrence (ca. 3,411.9 km 2).
Relationships: — Croton carajasensis is a monoecious shrub, with stellate trichomes, leaf nectaries at the base and margins of the blade, inflorescence with unisexual cymules at the base, stamens usually 11, pistillate flowers with unequal sepals or lobes of calyx and bifid styles; therefore it belongs to Croton sect. Geiseleria (Gray 1856: 391) Baillon (1858: 359), according to the concept of van Ee et al. (2011). Among the subsections of Geiseleria recognized by Riina et al. (2021), C. carajasensis appears to be a member of C. subsect. Geiseleria (Gray 1856: 391) B.W. van Ee & P.E. Berry in Riina et al. (2021: 135), in virtue of its inflorescences with staminate flowers continuous with the pistillate ones, without a distinct sterile space between them, and pistillate flowers with 5 strongly unequal sepals. Despite this, the subsections of C. sect. Geiseleria still need to be better defined morphologically, and the position of C. carajasensis in any of them needs to be evaluated using molecular phylogenetic evidence.
Croton carajasensis can be confused with C. abaitensis, C. adamantinus, C. harleyi and C. ramosissimus because all are densely branched subshrubs or shrubs, with tomentose indumentum of stellate trichomes on the branches and abaxial surface of the leaves, foliar nectaries at the base and in the sinuses of the margin, ovate, oval-lanceolate or elliptic leaf blades with slightly cordate or obtuse base, generally short (up to 4 cm long) thyrses, prominent bracts (often longer than 2 mm long), 2-fid styles, and fruits with accrescent sepals. Despite this, C. carajasensis differs from the species mentioned above by a set of characters, as shown in Table 1.
Croton carajasensis also shows relative similarity to C. amaraliae Riina & P.E. Berry in Riina et al. (2021: 123) and C. strobiliformis Secco (2009: 249), which also occur in the state of Pará in open vegetation of the Amazonian Phytogeographic Domain. However, C. carajasensis can be easily differentiated from both species by the secondary branches arising alternate from the main branches (vs. arising in bifurcations or trifurcations in C. amaraliae and C. strobiliformis), leaf blades with obtuse or rounded base and penninerved with 3 veins coming out of the base (vs. cordate and palmatinerved with 5 or 7 veins coming out of the base in C. amaraliae and C. strobiliformis), basilaminar cupuliform nectaries inconspicuous to the naked eye (vs. stipitate-patelliform and conspicuous in C. amaraliae and C. strobiliformis), petioles 0.2–1.8 cm long (vs. 1.5–3 cm long in C. amaraliae and 1.5–7 cm long in C. strobiliformis), inflorescences 2–4 cm long with 2–4 pistillate flowers at base (vs. 4.8−10.5 cm long with 6−12 pistillate flowers in both species), petals absent in pistillate flowers (vs. present but rudimentary in both species), staminate flowers with sepals, petals and stamens with 2.5–3, 3–4.5, and 4.5–6 mm long, respectively (vs. 1.3–1.9, 2–2.5, and 3–3.5, respectively, in C. amaraliae and C. strobiliformis) and also capsules with 5–7.5 mm diam. (vs. 3.5–4.3 mm diam. in C. amaraliae and 5.5–6 mm diam. in C. strobiliformis). Croton strobiliformis was synonimized under C. parodianus by Sodré et al. (2019), who adopted a broad circumscription for the species. However, considering the description of the new species C. amaraliae by Riina et al. (2021) from collections identified as C. parodianus by Sodré et al. (2019), we conclude that the broad circumscription of C. parodianus should be reassessed, and C. strobiliformis considered a valid species.
Specimens of Croton carajasensis have been identified in herbaria as Croton goyazensis Müller Argoviensis (1865: 120) (e.g., Berg & Henderson BG 458), probably because of the whitish or grayish indumentum of branches and leaves. However, C. carajasensis is easily distinguished by the cupuliform leaf nectaries, thyrses up to 4 cm long, bracts ca. 2–2.2 mm long, pistillate flowers with pedicel 1–2.5 mm long and sepals conspicuously unequal, 3.5–7 mm long sepals, and globose capsules with accrescent sepals, while C. goyazensis has subcylindrical or conical nectaries, thyrses 2−8(−14) cm long, bracts 1–2 mm long, pistillate flowers with a pedicel 3−5.7 mm long and equal sepals 1.9−2.8 mm long, and oblong capsules with discreet and not accrescent sepals.
Additional specimens examined (paratypes):— BRAZIL. Pará: Canaã dos Carajás, Floresta Nacional de Carajás, Serra Sul, S11A, 6°19’27”S, 50°27’11.5”W, 650 m elev., 20 July 2012, fl., fr., A.J. Arruda et al. 1189 (BHCB, MG); FLONA de Carajás, Serra dos Carajás, córrego seco próximo à Lagoa do Jacaré, 6°21’20”S, 50°23’26”W, 672 m elev., 19 October 2016, L.V. Vasconcelos et al 1036 (MG); Serra Sul, 694 m elev., 01 December 2015, J. Trindade et al. 346 (MG); Lagoa temporária, 6°24’31”S, 50°21’6”W, 29 September 2015, fl., L. Maielo s.n. (HSTM); S11B, 6°21’31”S, 50°23’25”W, 731 m elev., 02 December 2015, fl., fr., J.L.C. Costa et al. 23 (MG); Serra Sul, 01 December 2015, J.L.C. Costa et al. 07 (MG); S11C, 6°24’00”S, 50°23’20”W, 02 December 2015, fl., fr., C.S.P. Dias et al. 02 (BHCB, MG, RB); S11D, 6°23’38”S, 50°21’59”W, 743 m elev., 01 December 2015, fl., fr., J.L.C. Costa et al. 18 (MG); Parque Nacional dos Campos Ferruginosos, Serra do Tarzan, 6°19’47”S, 50°07’52”W, 731 m elev., 01 September 2015, fl., fr., R.M. Harley 57340 (MG); Curionópolis, Serra Leste, Companhia Vale do Rio Doce, 5°58’36”S, 49°38’38”W, 20 January 2005, fl., fr., L.V.C. Silva & C.S. Rosário 22 (MG); Marabá, Serra dos Carajás, acamp. 1, 700 m elev., 20 August 1972, fl., N.T. Silva & B.S. Ribeiro 3560 (IAN); Parauapebas, Floresta Nacional de Carajás, Serra Norte near AMZA Exploration camp, ca. 6°0’S, 50°15’W, 600 m elev., 11 October 1977, C.C. Berg & A.J.A. Henderson BG 458 (INPA, MG, NY, RB, US); 25–30 km NW of Serra Norte, 5°55’S, 50°26’W, 05 December 1981, fl., fr., D.C. Daly et al 1701 (F, HRB, IAN, INPA, MG, MO, NY, US); Serra Norte, N3, 07 December 1988, fl., fr., N.A. Rosa & F.C. Silva 5187 (MG); Serra Norte, N1, 19 August 1992, R.S. Secco & R. Bahia 822 (MG); ibid., 6°02’47”S, 50°17’3”W, 23 November 2009, fl., fr., R.D. Ribeiro et al. 1342 (RB); ibid., 6°02’39”S, 50°16’15”W, 701 m elev., 04 February 2015, fl., fr., L.V.C. Silva & T.B. Jorge 1417 (BHCB); ibid., 707 m elev., 09 January 2018, L.C. Barbosa 19 (MG); Serra Norte, N2, 6°03’23”S, 50°15’11”W, 677 m elev., 04 February 2015, fl., fr., L.V.C. Silva & T.B. Jorge 1415 (BHCB, MG); ibid., 681 m elev., 04 February 2015, L.V.C. Silva & T.B. Jorge 1425 (BHCB); Parque Nacional dos Campos Ferruginosos, Serra da Bocaina, 6°18’52”S, 49°54’08”W, 714 m elev., 15 December 2010, fl., fr., N.F.O. Mota et al. 1885 (BHCB).
description: Published as part of Sodré, Rodolfo Carneiro & Secco, Ricardo De S., 2023, Croton carajasensis, a new species from Serra dos Carajás, Pará, Brazilian Amazon, pp. 133-141 in Phytotaxa 630 (2) on pages 134-138, DOI: 10.11646/phytotaxa.630.2.4, http://zenodo.org/record/10376947