Croton maranonensis Riina & Martín-Muñoz, 2024

Martín-Muñoz, Juan, Silva, Elienai Cândida e, Gonzáles, Paúl, Muñoz-Sánchez, Álvaro, Cumbicus, Nixon, Goodwin, Zoë, Meira, Renata Maria Strozi Alves & Riina, Ricarda, 2024, Croton maranonensis: a new species of Euphorbiaceae from the tropical inter-Andean dry valleys, European Journal of Taxonomy 947, pp. 289-308 : 292-300

Croton maranonensis Riina & Martín-Muñoz sp. nov.

urn:lsid:ipni.org:names:77347325-1

Figs 1–2

Diagnosis

Croton maranonensis sp. nov. is morphologically most similar to C. hondensis and can be distinguished from the latter mainly by its bifid styles (4-fid in C. hondensis ), shorter petioles (0.2–1 cm vs 1.8–5.3 (–7.8) cm in C. hondensis ),leaf blades that are2–6(–8) cm long (5.5–6.6 (–10.2) cm long in C. hondensis ), bracts 1–1.2 mm long (3.2–5 mm in C. hondensis ) and the presence of a conspicuous, usually persistent, colleter at the leaf apex (vs an incospicuous caducous colleter in C. hondensis ) ( Table 1 ).

Etymology

The specific epithet of the new species refers to Marañón river valley, the location where the majority of specimens of C. maranonensis sp. nov. have been collected.

Type material

PERU • Amazonas, Utcubamba, Dtto. Bagua Grande, carretera Corral Quemado a Lonya Grande, bordeando el valle del alto Río Marañón ; 06°04′20″ S, 78°32′24″ W; elev. 600 m; 20 May 2004; R. Riina & J. Campos 1469; holotype: MA [ MA 874921 ], isotypes: E, MICH, MO, USM .

Other material examined

ECUADOR • Loja, Cantón Catamayo, Parroquia el Tambo, sector San Bernabé, 500 m de la entrada del desvío desde San Bernabé a Malacatos ; 04°05′32.2″ S, 79°20′11.8″ W; elev. 1950 m; 23 Nov. 2013; N. Cumbicus, F. Tinitana & O. Cabrera 1890; HUTPL • Loja, Cantón Catamayo, Parroquia el Tambo, sector San Bernabé, 500 m de la entrada del desvío desde San Bernabé a Malacatos ; 04°05′32.2″ S, 79°20′11.8″ W; 1950 m; 20 May 2008; N. Cumbicus & V. Camacho 1924; HUTPL, MA .

PERU • Amazonas, Bagua Grande, El Parco, bosque seco espinoso ; 05°40′00″ S, 78°25′00″ W; elev. 700 m; 5 Dec. 2001; R. Vásquez, R. Rojas & L. Campos 27094; MO, USM [ 198077 ], WIS • Amazonas, along road Bagua Grande and Pedro Ruiz in dry and semideciduous scrub ; 05°54′48″ S, 78°07′38″W; elev. 500–1000 m; 10 Mar. 1998; H. van der Werff, B. Gray, R. Vásquez & R. Rojas 14623; MICH, MO, WIS • Amazonas, Bongorá, Pedro Ruiz-Chachapoyas, km 35 ; 06°12′53″ S, 77°54′21″ W; Oct. 1990; F. Kahn & F. Moussa 2854; USM [ 115945 ] • Amazonas, Along road Tingo-Kuelap, Choctamal, moderately wet scrub, originally forest; 06°23′43″ S, 77°57′53″ W; elev. 2400 m; 12 Mar. 1998; H. van der Werff, B. Gray, R. Vásquez & R. Rojas 14806; USM [ 201908 ] • Cajamarca, Jaén ; 9 Jun. 1877; E.D. Andre 4713; K • Amazonas, Valley of the Marañón river, past Tingo on road to Lambeyeque, property of Lola and Perico Heredia, on eastern bank of Rio Utcubamba ; -6.432583333, -77.87330556; elev. 1820 m; 8 Mar. 2012; K.G. Dexter, J.L. Marcelo Peña, A. Daza Yomona & R.T. Pennington 5935; E • Cajamarca, Jaén, 29 km E of Pucara on road to Bagua, very dry tropical forest along Río Huancabamba ; elev. 710 m; 10 Jun. 1978; A. Gentry, M. Dillon, J. Aronson & C. Diaz 22750; F [ 2100677 ], MICH • Cajamarca, Jaén, Dtto. Jaén, Sector El Huito, bosque seco ; 05°40′47″ S, 78°47′55″ W; elev. 890 m; 18 Jul. 2005; J.L. Marcelo-Peña, A. Tapia N. & J. Dilas J. 1761; MICH, MOL • Cajamarca, Jaén, Yanayacu, bosque seco ; 05°40′47.8″ S, 78°46′12.3″ W; elev. 623 m; J.L. Marcelo Peña 2057; MOL • Cajamarca, Jaén, El Huito, bosque seco ; 05°41′17″ S, 78°48′60″ W; elev. 780 m; 14 Dec. 2006; J.L. Marcelo Peña & U. Hipler 2235; MOL • Cajamarca, Jaén, Dtto. Jaén, Sector San Isidro, bosque estacionalmente seco ; 05°42′30″ S, 78°46′54.4″ W; elev. 734 m; 18 Apr. 2007; J.L. Marcelo-Peña & V. Marcelo-Peña 2601; MICH • Cajamarca, Dtto. Jaén, Sector El Huito, bosque excepcionalmente seco ; 05°41′17″ S, 78°48′59″ W; elev. 780 m; 24 Mar. 2008; J.L. Marcelo-Peña, C. Carrasco & R. Carhuatocto 3107; E [ E00664543 ] • Cajamarca, Jaén, Pucará (On the Río Huancabamba), km 127 east of Olmos, north of town up creek in Quebrada de las Breas in vicinity of waterfall, ca 20 minutes by foot ; 05°58′17.6″ S, 79°11′59.5″ W; 11 Jan. 1964; P.C. Hutchison & J.K. Wright 3520; F, K [ 000111643 ], USM • Cajamarca, Jaén, at Gota de Agua, privately owned conservation área 15 minute drive away from central Jaén. Collected as part of plot work, plot located close to a path leaving from the main gate of the estate ; 05°41′33″ S, 78°46′04″ W; elev. 800 m; 9 Apr. 2008; T.E. Sarkinen, A. Daza, H. Vandrot & S. D’ugard 3026; E [ E01007877 ], FHO, MOL, USM • Cajamarca, Jaén, Dtto. Morro Solar, camino de Jaén a Chililique. Ladera con vegetación seca, suelo arenoso y pedregoso ; 05°43′02″ S, 78°48′56″ W; elev. 700 m; 22 May 2004; R. Riina & J. Campos 1478; MA • Cajamarca, Jaén, Pucará, bosque secundario , 06°03′00″ S, 79°10′00″ W; elev. 1000 m; 28 Dec. 1999; R. Rojas, J. Campos & S. Flores 863; WIS • Cajamarca, Jaén, Colasay, bosque seco ; 05°55′00″ S, 79°10′00″ W; elev. 1600 m; 8 Dec. 2001; R. Vásquez, R. Rojas & L. Campos 27200; USM [ 196679 ], WIS • Cajamarca, Jaén, dry scrub along Marañón, between Chamayo and Corral Quemado ; 05°42′ S, 78°48′ W; elev. 700 m; 25 Mar. 2001; H. van der Werff, R. Vásquez & B. Gray 16399; USM [ 178708 ] • Cajamarca, San Ignacio, Distrito de Chirinos, Patociego ; 05°19′ S, 78°44′ W; elev. 500–800 m; 27 Jan. 1996; J. Campos & O. Díaz 2210; MO, MOL • Cajamarca, San Ignacio, Dtto. Chirinos, La Catahua , 05°24′ S, 78°47′ W; elev. 500– 800 m; 24 Jan. 1996; J. Campos 2139; MA, MICH, MO, USM • Dtto. La Libertad, Sánchez Carrión, Chugay, 4 km abajo El Convento en la ruta Huamachuco - Calemar ; 07°36′21″ S, 77°51′45″ W; elev. 1695 m; 16 Feb. 2020; P. Gonzáles, Z.A. Goodwing, J.L. Marcelo-Peña, W. Aparco & R. Balvin 6491; E [ E01059878 ], USM • Dtto. La Libertad, Sánchez Carrión, Chugay, 4 km abajo El Convento (margen derecho del Río Chusgón ); 07°36′21″ S, 77°51′45″ W; elev. 1695 m; 13 Feb. 2020; J.L. Marcelo-Peña, P. Gonzáles, Z.A. Goodwin, W. Aparco & R. Balvin 11142; E, USM • Dtto. La Libertad, Sánchez Carrión, Chugay, 4 km abajo El Convento (margen derecho del Río Chusgón) ; 07°36′21″ S, 77°51′45″ W; elev. 1695 m; 13 Feb. 2020; J.L. Marcelo-Peña, P. Gonzáles, Z.A. Goodwin, W. Aparco & R. Balvin 11146; E, USM .

Description

Monoecious shrub, up to 2 m high; young branches with dense indumentum of stellate trichomes, often stipitate; without evident latex. Stipules 0.5–3 mm long, linear to narrowly subulate, with colleters (ovoid glands) at the base, margin, and apex. Petiole 0.2–1 cm long, with dense indument of stellate trichomes and stipitate stellate trichomes; petiolar nectary glands absent; colleters present at the apex of petioles, sometimes arranged into two clusters at both sides of the petiole. Leaf blade ovate-lanceolate 2–6(–8) × 1–2(–4) cm; indumentum on the adaxial side more or less dense with stipitate porrect stellate trichomes, simple trichomes also present; indumentum on the abaxial side very dense with long-stipitate porrect stellate trichomes; base cordate or rounded, sometimes asymmetrical; apex acute, usually mucronate with a single conspicuous colleter (no longer active); margin entire; colleters (no longer active) along the margin; venation palmate-pinnate, 3–5 veined at base, brochidodromous; primary and secondary veins raised only on the abaxial side. Inflorescences terminal, 2–4.5 cm long, axis slightly costate, with a dense indumentum of mostly stipitate porrect stellate trichomes, bracts linear and curved, ca 1–1.2 mm long; basal cymules pistillate; upper cymules with staminate flowers, all flowers regularly spaced or sometimes with a gap in the middle, between the pistillate and staminate portions, with persistent bracts and rounded scars of the fallen flowers. Staminate flowers pedicellate; pedicel 0.5–2.0 mm; sepals valvate, triangular-ovate, 1.3–2.0 × 1.0– 1.2 mm, adaxial side glabrous with simple trichomes at the apex, abaxial surface with a dense indumentum of stellate trichomes; petals narrowelliptic 1.2–2.0 × 0.5–0.7 mm, simple trichomes scattered on adaxial side and toward the apex, abaxial side glabrous; receptacle densely pilose; stamens 11–12, filaments 2.5–3.0 mm long, with trichomes toward the base, anthers 0.6–0.8 × 0.3–0.5 mm. Pistillate flowers pedicellate, pedicel 0.5–1 mm long; sepals triangular-ovate, valvate, unequal, the 3 large sepals 1.8–2.0 × 0.8–1.2 mm, often with a dissected margin, sometimes with a long acuminate apex, the 2 small sepals 1.0–1.2 × 0.3–0.5 mm, with margin entire, adaxial and abaxial sides with stellate trichomes; petals absent; nectary disc entire; ovary densely covered with stellate trichomes; styles bifid, covered in part with stellate trichomes. Fruits subglobose, 4.0–5.0 × 3.0– 3.5 mm, columella 2.5–3.0 mm long; seeds elliptical, 2.7–3.0 × 1.3–1.5 mm, usually mottled (brownish with black spots), surface slightly foveolate, shiny; caruncle 0.2–0.3 × 0.2–0.3 mm. ( Figs 1–2 ).

Main micromorphological features of Croton maranonensis sp. nov.

Leaves are amphi-hypoestomatic, with paracytic stomata and epidermal cells exhibiting straight contour ( Fig. 3A )on both faces.Simple trichomes and stipitate stellate porrect trichomes were present( Figs 3B–C ); trichome stipes were shorter on the adaxial sides than on the abaxial side. Sometimes idioblasts were observed at the base of the radial cells of stellate trichomes ( Fig. 3D , in detailed image). Sclereids, connecting both leaf sides across the mesophyll, were present at the base of stellate trichomes ( Fig. 3E ). Unicellular, glandular trichomes were relatively abundant on the abaxial side ( Fig. 3C ) and rare on the adaxial side ( Fig. 3B ). Glandular trichome had a knob-like appearance with a narrow base and a dilated distal portion ( Figs 3F–G ). Epidermal cells were tabular with mucilage content ( Fig. 3F ); the mesophyll is dorsiventral ( Fig. 3F ). The contour of the midrib is biconvex, with 2–3 layers of annular subepidermal collenchyma ( Fig. 3D ).

The bicolateral vascular system is organized in an open arch with a dorsal bundle ( Fig. 3D ). The blade margin is straight with non-continuous palisade parenchyma ( Fig. 4A ). The petiole has a flat-convex shape ( Fig. 4B ) and is covered by a uniseriate epidermis. Three to five subepidermal layers of annular collenchyma surround the entire petiole ( Fig. 4B ). The bicolateral vascular system is organized in a closed arch with the bundles separated by parenchyma ( Fig. 4B ). Both young and fully expanded leaves present standard colleters scattered along the blade margin ( Figs 4A, C ). Clusters of colleters were observed at the base of stipules ( Fig. 4D ) and on the basilaminar/acropetiolar region of the leaf ( Fig. 4F ), while only a single colleter was present at the stipule apex ( Fig. 4E ). Standard colleters consist of one-layer secretory palisade epidermis, and parenchyma, which are vascularized by xylem and phloem ( Fig. 4A, E ). Idioblasts with druse occur in the mesophyll ( Fig. 3F ), midrib, and petiole. Non-anastomosed articulated laticifers ( Fig. 4G ) were observed in shoots and fully expanded leaves, always associated with phloem, often exhibiting a Y-shaped form ( Fig. 4H ). Specimens of C. flavispicatus and C. triqueter had similar anatomical features ( Fig. 4I ), with the exception of the presence of a pair of accessory bundles in the petiole ( Fig. 4J , Table 1 ), which was absent in C. maranonensis sp. nov. ( Fig. 4B ), and the absence of simple trichomes on the blade abaxial side. The presence of simple trichomes on the abaxial side of the blade ( Fig. 4I ) and the occurrence of idioblasts at the base of the radial cells of stellate trichomes of C. triqueter were the only anatomical differences observed between C. triqueter and C. flavispicatus .

Phylogenetic placement and relationships

The ITS matrix, with 63 aligned positions, consisted of 32 sequences representing 24 species of Croton , including 9 from the focal group ( C. sect. Julocroton ). Overall the topology of the represented Croton clades or sections ( Fig. 5 ) was congruent with previous Croton phylogenetic analyses ( Berry et al. 2005; Van Ee et al. 2011). Croton sect. Julocroton , C. sect. Lasiogyne (Klotzsch) Baill. and C. sect. Heptallon (Raf.) Müll.Arg. were recovered as highly supported monophyletic groups (Posterior Probability, PP = 1). The three specimens of C. maranonensis sp. nov. were clustered together in a highly supported clade (PP = 1) within the C. sect. Julocroton clade. The new species was recovered sister to a clade including C. triqueter , C. flavispicatus , C. hondensis , C. conspurcatus Schltdl. and C. fuscecens Spreng. , albeit with relatively low support (PP = 0.79). The three accessions of C. hondensis and the two specimens of C. fuscescens were recovered as monophyletic groups, while the four representatives of C. triqueter emerged as unresolved within the largest clade including C. flavispicatus , C. hondensis , C. triqueter , and C. conspurcatus . The clade including C. argenteus was recovered sister to the rest of the C. sect. Julocroton .

Distribution, ecology, and phenology

Croton maranonensis sp. nov. is distributed in the Marañón Valley in northern Peru and in the Province of Loja, southern Ecuador. According to information from specimens labels, the species grows in seasonally dry tropical forest and dry shrublands, along semideciduous shrubs from different plant families, giant columnar cacti, ferns, and epiphytic bromeliads ( Fig. 6 ). Examined specimens were in flower and fruit throughout the year.

Preliminary conservation status assessment

The extent of occurrence (EOO) and area of occupancy (AOO) resulted in 26,335.574 km 2 for EOO and 72,000 km 2 for AOO. Following the IUCN criteria ( IUCN 2012), Croton maranonensis sp. nov. cannot be classified as vulnerable (VU) using the B1 criterion due to its disjunct distribution with relatively isolated populations in southern Ecuador and a few records (Gonzáles 6491 and Marcelo-Peña 11142, 11146) collected upstream (south) in the Marañón Valley ( Fig. 5 ). For this reason we classify the species tentatively as nearly threatened (NT).

Figures

Fig. 1. Croton maranonensis sp. nov. A. Image of the holotype: MA[874921]. B. Clusters of no longer active colleters at the base of the lamina. C. Detail of the stipules. D. Leaf apex bearing a colleter (no longer active) at the tip. E. Seeds in different views. F. Inflorescences showing mainly the staminate portion (distal) with flowers in bud. G. Individual staminate flower. H. Detail of the calyx showing the three conspicuous and dissected lobes and the two highly reduced ones. I. Detail of the fruit showing the bifid styles. A from R. Riina & J. Campos 1469 (MA); B, E from van der Werff 14623 (MICH); C from Rojas 0863 (WIS); D, F. from van der Werff 16399 (WIS); G from Campos 2139 (MICH, MO); H–I from Cumbicus & Camacho 1924. Scale bars: B, D = 500 µm; C, F = 2 mm; E, G–I = 1 mm.

Fig. 2. Croton maranonensis sp. nov. A. Small individual growing in dry forest understory. B. Fertile branch. C. Inflorescence showing both pistillate and staminate flowers; note the conspicuous colleter at the apex of the leaf on the right. D. Detail of inflorescence with two staminate flowers in anthesis. E. A view of the open dry vegetation associated with the seasonally dry tropical forest in the Marañón Valley where the new species occur. A–B from R. Riina 1478; C from Cumbicus 1924; D from Gonzáles 6491. Photographs by R. Riina (A–B), N. Cumbicus (C), and P. Gonzáles (D–E).

Fig. 3. Leaf anatomy features of Croton maranonensis sp. nov., based on diaphanization of leaf blade (A); scanning electron microscopy from the adaxial (B) and abaxial (C) surface; and transverse sections (D–G). A. Cells with straight contour and paracytic stomata (st) on the adaxial surface. B. Epidermal appendages of simple (s) and porrect (p) stellate trichomes (tr) with a variable number of radial cells. C. Porrect stellate trichomes and knob-like glandular trichomes (g). D. Biconvex midrib and secretory idioblast (id) at the base of the stellate trichome in detail. E. Simple trichomes connected to sclereids crossing the mesophyll (arrow).F. Middle region of the blade with dorsiventral mesophyll and knob-like glandular trichome (g) on the abaxial side; note druses (arrow head only) dispersed on the mesophyll and sclereid (arrow). G. Knob-like glandular trichome on the adaxial side. Abbreviations: co: collenchyma; db: dorsal bundles; ep: epidermal cells; g: glandular trichome; id: idioblast; p: porrect ray; ph: phloem; pp: palisade parenchyma; s: simple trichome; sp: spongy parenchyma; st: stoma; tr: trichome; x: xylem. Scale bars: A–C = 20 µm; D = 100 µm (detail = 20 µm); E–G = 50 µm.

Fig. 4. Leaf anatomy features of Croton maranonensis sp. nov. (A–H), C. triqueter Lam. (I) and C. flavispicatusRusby (J), basedon transverse (A, B, F–J) and longitudinal(G–H)sections; diaphanization of leaf blade (C) and stipules (D–E). A. Blade margin with non-continuous palisade parenchyma; note standard vascularized coléter in detail (asterisk). B. Petiole with bicollateral vascular system organized in a closed arch with the bundles separated by parenchyma and without accessory bundles. C. Standard colleters along the margin, note vascularization at the base (asterisk). D. Clusters of vascularized (asterisks) colleters (cl) at the base of the stipule. E. A single colleter at the apex of the stipule, note the vascularization at the base (asterisk). F. Cluster of basilaminar/acropetiolar colleters at both sides of the petiole. G. Non-anastomosed articulated laticifers; note the transverse walls (arrow head) and the latex content (star). H. Y-shaped laticifers (star). I. Dorsiventral mesophyll and simple trichome (s) on abaxial surface. J. Petiole with bicollateral vascular system organized in a closed arch with the bundles separated by parenchyma and one pair of accessory bundles (arrow). Abbreviations: cl: colleter; co: collenchyma; ep: epidermal cells; pa: parenchyma; ph: phloem; pp: palisade parenchyma; s: simple trichome; sp: spongy parenchyma; st: stoma; x: xylem. Scale bars: A, D = 100 µm; B–C, F, J = 200 µm (detail of C = 20 µm); E, I = 50 µm; G–H = 10 µm.

Fig. 5. Bayesian phylogram based on ITS sequences of the selected Croton species including C. maranonensis sp. nov. and representatives of sections Julocroton, Lasiogyne, Heptallon, and other sections of Croton. Numbers at nodes indicate Bayesian posterior probability values (PP). Numbers distinguishing accessions of the same species are also indicated in Appendix 2. The country of origin of the sample is indicated only for the samples of the new species..

Fig. 6. Map showing the location of the known herbarium collections of Croton maranonensis sp. nov. (solid circles). Main cities in the area are indicated by white triangles.