Ixchelia kochii Cuevas, 2019

Guzmán, Ramón Cuevas, Sánchez Rodríguez, Enrique V. & Núñez López, Nora M., 2019, Ixchelia kochii (Violaceae, Rinoreeae), a new species from western Mexico and the third one of the genus, Phytotaxa 391 (2), pp. 143-148 : 146-147

Ixchelia kochii Cuevas , sp. nov. ( Figs. 1 & 2 )

Type: — MEXICO. Jalisco: Mpio. Cuautitlán, ejido Ayotitlán, cerro de La Antena, elev. 1429 m, UTM 594198, 2144600 WGS84, 5 julio 2018 (fl), R. Cuevas, J. L. Mendoza y E. V. Sánchez 12891 (holotype: ZEA; isotypes: IBUG, MEXU, IEB) .

Ixchelia kochii is similar to I. uxpanapana , but differs from it by having leaves with an acute to acuminate apex, when acuminate the acumen usually ˂ 1 cm long; staminal tube with 5 dorsal glands of larger size; and a bi- or tricarpellar ovary with 2–3 ovules and a deeply 2–3-lobed stigma.

Tree 5–14 m high, mostly 12–25 cm in diameter; outer bark whitish, scaly, the internal yellowish with slight transparent to milky exudate. Branchlets hanging, whitish, cylindrical to laterally compressed, 0.8–1.2 mm in diameter, pruinose, glabrous or with some hairs on one side. Stipules of laminar leaves soon deciduous, free, ovate, 1.2–1.6 × 0.8–0.9 mm, costate, scarious, base asymmetric, margin erose to ciliate, apex acuminate, glabrous or with some hairs on the back; stipules of scale-like leaves persistent, ovate, 0.8–1.1 × 0.5–0.6 mm, costate, base asymmetric, margin erose to ciliate, apex acuminate, glabrous or with some hairs on the back. Phyllotaxy spiraled to subopposite toward the apices of the branchlets. Petioles of laminar leaves articulate at base, semiterete and adaxially complanate, (3) 5–10 × 0.4–0.6 mm, adaxial surface with antrorse hairs 0.4–0.6 mm long; laminas elliptic, (2.5) 5–11.7 × (1.7) 2–4 cm, the young membranous, the mature coriaceous, cuneate at base, margin serrate to serrulate, teeth frequently glandular, apex acute to acuminate, glabrous on both sides, lateral veins 7–12 pairs; scale-like leaves at bases of branchlets sessile, narrowly ovate to ovate, 0.8–1.2 × 0.4–0.5 mm, concave, apex acuminate, glabrous on both sides. Floral buds 2–3 per axil, whitish, ovoid, 0.75–1.6 × 0.7–1.2 mm; bracts and bractlets ovate to broadly ovate, 0.5–1.4 × 0.3–0.4 mm, concave, costate, margin erose to ciliate, apex acute to acuminate, glabrous or often with antrorse hairs on the back. Inflorescences axillary, lateral or subterminal, 1–3 per node; peduncle 0.2–0.3 mm long, covered by bracts and bractlets; pedicels articulate at base, filiform, 4.5–6 × 0.3–0.5 mm, glabrous. Flowers pendulous, slightly perigynous, 3–3.5 × 3–3.2 mm; calyx 1.6–1.8 mm long, of 5 subequal lobes united 1/4–1/3 of their length, lobes 1.1–1.6 × 0.7–1 mm, margin ciliate, apex obtuse to acuminate, glabrous on both sides; corolla of 5 subequal petals, these free, yellow, elliptic, 1.7–2.6 × 1–1.4 mm, concave, margins revolute, scarious, repand to erose, apex obtuse to acuminate; stamens 5, forming a staminal column crowned by laminar appendages, filaments connate into tube 0.2–0.4 mm high; dorsal glands 5, adnate to base of staminal tube, white to brown, oblong, 0.4–0.8 × 0.2–0.3 mm, membranous, apex truncate, emarginate or bifid, glabrous; anthers sessile, dithecal, longitudinally dehiscent, oblong, 0.8–1.1 × 0.5–0.8 mm, glabrous; connective scales lateral as well as apical, laminar, orange-brown, triangular-ovate, 0.7–0.9 × 0.4–0.8 mm, membranous, bases cordate and imbricate, apex acute, glabrous; ovary tricarpellate sometimes bicarpellate, unilocular, subglobose, 0.4–0.6 mm in diameter, glabrous, placentation parietal with 2–3 ovules; style filiform, straight to distally sigmoid, 1–1.2 mm long; stigma bi- or trifurcate, lobes exceeding the staminal column, 0.2–0.3 mm long, glabrous. Capsule dehiscent into three subequal valves, subglobose, 6–7 × 5–6 mm, green, smooth, glabrous, the valves compressed laterally and with reticulate venation, calix persistent at base of fruit, mature fruit bearings the persistent style; seeds usually three by fruits sometimes two, subspherical-ellipsoid, 3.2–3.8 × 2.7–3 mm, black to brown-black with light spots, shiny, glabrous.

Distribution, habitat and phenology:— Ixchelia kochii is currently known only from the type locality in the municipality of Cuautitlán, in the state of Jalisco at the border with the state of Colima. It occurs in gullies in the ecotones between tropical subdeciduous forest and montane cloud forest, where it is associated with such tree species as Aphananthe monoica (Hemsl.) J.-F. Leroy (1961: 74), Beilschmiedia manantlanensis Cuevas & Cochrane (1999: 18) , Calliandra laevis Rose (1899: 194) , Inga vera Benth. subsp. eriocarpa (Benth.) J. León (1966: 338) , Oreopanax peltatus Linden (1859: 368) , Prunus cortapico Kerber ex Koehne (1915: 307) , Styrax radians P.W. Fritsch (1997: 745) , Trema micrantha (L.) Blume (1856: 58), and shrubs such as Brachistus stramoniifolius (Kunth) Miers (1849: 263) and Chamaedorea pochutlensis Liebm. (1849: 308) , and the creeping herb Aristolochia manantlanensis Santana Mich. (2007: 82) .

Ixchelia kochii is ephemeral in its flowering, which occurs at the end of June and the beginning of July. The fruits ripen from the end of August to the middle of September.

Etymology:—The specific epithet honors Stephen D. Koch, who founded the Herbario-Hortorio (CHAPA) of the Colegio de Postgraduados and served as its curator until his death. He made more than 89,200 botanical collections, named 43 species of vascular plants new to science, and served as a mentor to many students, some of whom now are specialists in plant systematics.

Conservation Status:—According to the categories and criteria of the IUCN Red List ( IUCN 2012), Ixchelia kochii is assigned a preliminary status of “Critically Endangered” (CRB2[abii] and C2[aii]). Its known and estimated geographical distribution is less than 10 km 2, it has been registered only from two localities with a projected decrease in area of occupation and habitat due to mining activity, and it has an estimated population size of fewer than 250 mature individuals.

Additional specimens examined:— MEXICO. Jalisco: Mpio. Cuautitlán, ejido Ayotitlán, entre el predio Los Juanes y puerta de acceso a La Minera Peña Colorada, cerro Las Antenas, elev. 1420, UTM 0594225, 2144610 WGS84, 25 Jul 2016 (ster), R. Cuevas, L. Guzmán y J. G. Morales 11646 ( ZEA) ; 23 Apr 2017 (ster), R. Cuevas, E. V. Sánchez, J. G. Morales y J. L. Mendoza 12280 ( ZEA) ; 13 Apr 2018 (ster), R. Cuevas, E. V. Sánchez y J. L. Mendoza 12700 ( ZEA) ; 5 Jul 2018 (fl), R. Cuevas, J. L. Mendoza y E. V. Sánchez 12894 ( ZEA) ; 5 Jul 2018 (fl), R. Cuevas, J. L. Mendoza y E. V. Sánchez 12899 ( ZEA) ; 30 Aug 2018 (fr), R. Cuevas, J. G. Morales y J. L. Mendoza 12941 ( ZEA) ; inmediaciones del poblado de La Astilla UTM 0594056, 2145117 WGS84, 30 Aug 2018 (fr), R. Cuevas, J. G. Morales y J. L. Mendoza 12926 ( ZEA) ; 30 Aug 2018 (fr), R. Cuevas, J. G. Morales y J. L. Mendoza 12927 ( ZEA) .

Discussion: —Based on morphological characteristics, the new species is placed in the genus Ixchelia : petiolate, laminar leaves; scale-like leaves on the bases of the branchlets; 1-flowered cymose inflorescences arising from condensed lateral or axillary short shoots; basally articulate pedicels; staminal filaments fused into a short tube; and 2 or 3 ovules per embryo sac. Unlike I. mexicana , I. kochii has a short hypanthium, the sepals being basally connate (sepals are free in I. mexicana ); solitary leaves subtending the branchlets and branches (instead of 1 to several leaves on blaquiblasts); petioles 3–10 mm long (vs. 0.5–1.5 mm long); elliptical blades with apex acute to acuminate (vs. rhombic-oblanceolate to obovate with apex rounded to subacute); and stigma deeply 2–3-lobate (vs. undifferentiated to weakly 3-lobed).

Ixchelia kochii is most closely related to I. uxpanapana , from which it differs by having leaves mainly acute (when acuminate, the acumen ˂ 1 cm long vs. leaves acuminate in I. uxpanapana , with an acumen 1–2 cm long); petals usually smaller (1.7–2.6 mm long vs. 2.1–3.8 mm long); dorsal glands 5, 0.4–0.8 mm long (vs. dorsal glands 1–3, 0.3 mm long); ovaries bi- or tricarpellar (vs. ovaries tricarpellar); ovules 2–3 per embryo sac (vs. ovules 3 per embryo sac); style shorter (1–1.2 mm long vs. 1.8–2.2 mm long); and stigma parted, 2–3-lobate (vs. stigma undifferentiated to weakly 3-lobate). Ixchelia kochii is found in western Mexico in the ecotones between tropical subdeciduous forest and montane cloud forest at 1260–1450 m elevation, whereas I. uxpanapana grows in eastern Mexico and central Panama in seasonal rain forest and tropical rain forest at elevations of 130–900 m ( Wahlert et al. 2015).

Ixchelia kochii has some significant features that are apparently seldom mentioned for the Violaceae , one being the presence of latex in the wood, although scattered secretory cells with yellowish content were reported by Cronquist (1981, p. 402). Also notable are the variation in carpel number and the pronounced stigmatic lobes, given that a tricarpellar pistil with a simple to weakly lobate stigma are common in the tribe Rinoreeae and the genus Ixchelia ( Hekking 1988, Wahlert et al. 2015). Incorporation of the proposed new species into Ixchelia requires expanding the circumscription of the genus to accommodate a wider range of diversity in the androecium, i.e., staminal tube with 1 to 5 dorsal glands, and in the gynoecium, i.e., carpels 2 or 3 with 2 or 3 ovules per embryo sac and stigmas undifferentiated or subdivided into lobes. Including I. kochii in genomic DNA studies would corroborate the correctness of its placement within the genus Ixchelia .

There is an urgent need to generate conservation and rescue measures for Ixchelia kochii , because its habitat is seriously threatened by ongoing mining activity.

Figures

FIGURE 1. A. Hanging branches and branchlets. B. Wood with latex. C. Branchlets with flowers. D. Margin of the laminar leaf with a glandular tooth. E. Stipules of laminar leaf. F. Scale-like leaves and their stipules. G. Node with three flowers. H. Calyx and staminal column crowned by laminar appendages.

FIGURE 2. A. Staminal tube, anthers and appendages, ventral side. B. Androecium and five dorsal glands and appendages. C. Pistil. D. Stigma deeply three lobate. E. Stigma deeply two lobate. F. Ovary inverted with three ovules. G. Fruits. H. Capsule dehiscent into three valves. I. Seeds.