Zanthoxylum unifoliolatum Groppo & Pirani, 2017

Groppo, Milton & Pirani, José Rubens, 2017, A new species of Zanthoxylum (Rutaceae) with a key to the species from Northeastern Brazil, Phytotaxa 314 (2), pp. 259-265 : 260-263

Zanthoxylum unifoliolatum Groppo & Pirani , sp. nov. Figures 1 A–J & 2 A–D .

Type:— BRAZIL. Sergipe: Nossa Senhora do Socorro, Floresta Nacional do Imbura, 10°50’34”S, 37°08’35”W, 3 May 2013 (pistl. pl.), Santana & Silva 162 (Holotype SPFR No. 16001!, Isotype ASE!).

The new species can be readily distinguished from other species of Zanthoxylum from Brazil by the presence of unifoliolate rather than pinnate leaves (with at least three leaflets), as observed in all other Brazilian species. It shares with Z. schrebei (from the Caribbean islands to northern South America) the unifoliolate leaves, but is immediately distinguished mainly by its female flowers with gynocieum of four carpels united by a discoid stigma (versus female flowers with only three carpels united in a capitate, slightly lobed stigma in Z. schrebei ).

Trees or shrubs 1–6 m tall, dioecious; branches with thorns up to 9 mm diam. enlarged at their base; young branches pilose, with scarce lenticels, indumentum of simple trichomes. Leaves alternate, 1-foliolate, spirally arranged; stipules absent; petiole 0.8–1.5 cm long; leaflet blade chartaceous, glabrous, with pellucid dots (spherical glands), scattered throughout the surface, 5.5–12 cm long, 2.7–7 cm wide, elliptic to obovate, apex acuminate, acute or rounded, sometimes emarginated, margin entire, base acute to obtuse; venation brochidodromous, midvein prominent on the abaxial surface, impressed to slightly prominent on the adaxial surface; secondary veins 7–13 pairs, prominent on the abaxial surface, impressed on the adaxial surface, uniformly diverging from midvein at angles of 52°–63°, intersecondary veins present, running in a larger angle than to major secondaries; petiole 5–15 mm long, articulate at its apex, glabrous. Inflorescence terminal, a thyrsoid up to 6 cm long, partial inflorescences ascending, up to 4 cm long, the proximal ones longer than the distal ones, inflorescence branches puberulous, cymes 1-flowered. Flowers 5- merous, actinomorphic, unisexual; petals whitish, buds ovoid to obovoid, 1–1.5mm long. Staminate flowers ca. 2 mm diam.; pedicel 1.5–2 mm long, puberulous; sepals deltoid, ca. 0.25 mm long, glabrous; petals oblong, apex acute, ca. 1 mm long, glabrous; stamens 5, ca. 0.8 mm long; filaments subulate, ca. 0.4 mm long; anthers ovoid, ca. 0.4 mm long, glabrous, with a glandular connective; pistillodium ca. 0.8 mm long, with 3–4 conical styles; ovary globose at base with a small locule containing 2–3 abortive, pendulous ovules; disc annular surrounding the base of the pistillodium. Pistillate flowers 2.5–3 mm diam.; pedicels 1–1.5 mm long, puberulous; sepals deltoid, glabrous, ca. 0.4 mm long; petals 2.0– 2.5 mm long, oblong, glabrous; staminodia 5, ca. 0.2 mm long; gynoecium of 4 carpels united only at the discoid stigma, ca. 0.8 mm diam., glabrous, depressed-globose, glandular-punctate, lifted by a gynophore. Fruit an oblique, 1-seeded, subglobose follicle (only one carpel developing), brownish, stipitate, ca. 3.5–4 mm long, surface with several rounded oil glands, glabrous; seed ca. 3.5– 2.5 mm, subglobose to reniform, black, shiny, pendulous by the persistent funicle. Embryo not seen.

Additional specimens examined (paratypes): — BRAZIL, Sergipe: Capela, Refúgio da Vida Silvestre, Mata do Junco , 10°32´10”S, 37°03´48”W, 19 April 2012 (stam. pl.), Gomes et al. 390 ( ASE, SPFR) ; Carmópolis , Serra das Cajazeiras, 23 April 2000 (fr.), Teles 6 ( IPA) ; Maruim , 10°43´00”S, 37°07´38”W, 22 May 2013 (pist. pl.), Gomes et al. 1091 ( ASE, SPFR) ; Nossa Senhora do Socorro, Floresta Nacional do Ibura , 10°50´32”S, 37°08´46”W, 18 August 2013 (fr.), Santana & Silva 109 ( ASE, SPFR) .

Etymology— The epithet “ unifoliolatum ” is a reference to the unifoliolate leaves of the species.

Vernacular name — The species is locally known as “laranjinha-do-mato” (meaning a small wild orange; Teles 6).

Notes and taxonomic affinities— The most remarkable trait in Zanthoxylum unifoliolatum is the presence of unifoliolate leaves, a characteristic that is unique within Brazil and very rare worldwide. Species of Zanthoxylum usually have imparipinnate (sometimes paripinnate) leaves, with some species reaching up to 65 leaflets per leaf [(as Z. foliolosum Donn.Sm. (1893:1) , from Central America)]. Very rarely scattered 1-to 3-foliolate leaves may occur on a plant [(e.g., Z. monogynum A.Saint-Hilaire (1824:150) , from Bolivia and Brazil, usually with 3–5(–7) foliolate leaves], while some species are characterized by bearing only bifoliolate leaves ( Z. bifoliolatum Leonard (1924:413) from the Greater Antilles). Z. schreberi (J.F. Gmelin 1791:498) Reynel in Bernal et al. (2015:6), an species from the Caribbean islands to northern South America, also bear only unifoliolate leaves and format and foliar dimensions are similar to those of Z. unifoliolatum . However, besides the evident allopatry, Z. unifoliolatum is distinguished by Z. schreberi mainly by its gynoecium of 4 carpels united by a discoid stigma (vs. 3 carpels with a capitate, slightly 3-lobed stigma). Characteristics of staminate flowers (as usual in Zanthoxylum ) as pistillodium format or shape of stamens are virtually identical in both species, but this is a common trait among the species of the genus. Other species that is morphologically similar to the new species is the partially sympatric Z. monogynum , with leaves 1(rarely) to 3–5(–7) foliolate leaves occurring on the same plant as seen above. The new species differs mainly in bearing all leaves with one leaflet [vs. (1–)3–5(7) leaflets in Z. monogynum ], smaller inflorescences reaching up to 6 cm long (vs. up to 12 cm), petals ca. 1 mm long (vs. 2–2.5 mm), staminate flowers with stamens shorter than the petals with filaments ca. 0.8 mm long (vs. exserted stamens with filaments up to 3 mm in Z. monogynum ), and also in its gynoecium, with four carpels in female flowers (vs. only one carpel, seldom 2, in female flowers of Z. monogynum ).

Distribution and habitat, phenology— Zanthoxylum unifoliolatum is known so far from a few collections made in the state of Sergipe, northeastern Brazil ( Fig. 3 ). The species is found in forested areas on sandy or sandy-clay soils in the Brazilian Atlantic Rainforest biome in the vicinities of Capela, Maruim, Nossa Senhora do Socorro and Carmópolis. In Carmópolis, the species is found on forested hills of the Serra das Cajazeiras. It has been collected with flowers from April to May and with fruits from April to August.

Uses— Local people use the leaves as an infusion for treating conjunctivitis and an ethanol solution is employed as a yellow dye. The wood was used in the past in carpentry (Dr. Aristônio Teles , pers. comm.).

Conservation status— Zanthoxylum unifoliolatum can be referred to as an Endangered Species (EN) according to the IUCN Redlist Categories and Criteria ( IUCN 2012). This species is known from only three localities in forests of the Brazilian Atlantic Rainforest biome, which has been suffering from a rapid process of deforestation ( Morellato & Haddad 2000, Ribeiro et al. 2009) with an estimated area of occurrence of less than 5000 km 2, which is projected to decrease (criteria IUCN B1a, B1bi, B1bii, B1biii). Fortunately, the species is found in protected areas such as Floresta Nacional do Imbura and Refúgio da Vida Silvestre Mata do Junco, in the municipalities of Nossa Senhora do Socorro and Capela.

Figures

FIGURE 1. Zanthoxylum unifoliolatum. A. Habit of male plant; B. Detail of branch with thorns; C. Staminate flower bud; D. Staminate flower, petals and one stamen removed (based on Gomes et al. 390). E. Detail of pistillate inflorescence; F. Pistillate flower, petals removed, st: staminodium; G. Petal from pistillate flower (based on Gomes et al. 1091); H. Fruit with pendulous seed; I. Open fruit. J. Seed (based on Santana & Silva 162). Illustrated by Bruno Simões Favaretto.

FIGURE 2. Zanthoxylum unifoliolatum. A. Thorns on trunk; B. Vegetation in Serra das Cajazeiras Carmópolis (Sergipe, Brazil), one of the places the new species was collected. C and D. Branches with pistillate inflorescences.

FIGURE 3. Geographic distribution of Zanthoxylum unifoliolatum.