Gonolobus sanmartinus Lozada-Pérez & E.B. Cortez, 2023

Lozada-Pérez, Lucio & Castro, Ericka Belén Cortez, 2023, A new species of Gonolobus (Apocynaceae) from Veracruz, Mexico, Phytotaxa 613 (1), pp. 69-74 : 70-72

Gonolobus sanmartinus Lozada-Pérez & E.B. Cortez , sp. nov.

Figs 1 , 2A–B , 3

TYPE:— MEXICO. Veracruz: Municipio San Andrés Tuxtla , 18°31’33“N, 95°10‘48“W, 1050 m, 22 April 2001, fl ., A. Rincón et al. 2332 (holotype XAL!, isotypes FCME!, MEXU!, MO!).

Gonolobus sanmartinus is similar to G. pallidus in foliar and flower size features, although in G. sanmartinus the lobes of the corolla are concave, the faucal ring is a slightly 5-lobed cup, densely pubescent, the stipe of the gynostegium is cylindrical, slightly keeled with 5 lobes adnate to the base, the gynostegial corona is a 5-lobed erect cup, dorsally striate. In contrast, G. pallidus presents flat corolla lobes, the faucal ring is an erect tube, visible as a 5-lobed edge, glabrate, the stipe of gynostegium is obconic, the gynostegial corona is tubular and 5-lobed, wider distally.

Vines up to 3 m tall, herbaceous, with white latex. Stems with mixed indumentum of three types of trichomes arranged in two rows, long pale-yellow and reflexed, 0.3–0.7 mm long trichomes, short trichomes and glandular, 0.05– 0.06 mm long. Leaves opposite, stipular colleters absent, petiolate, leaf blades elliptic to elliptic-oblong, dicolorous, 8.5–15 × 4–9 cm, apex short acuminate, base rounded, obtuse, acute to truncate, membranaceous, adaxially glabrate or with disperse long trichomes, abaxially with long straight dense trichomes, 0.3–0.4 mm, short and glandular trichomes absent, lateral veins 5–6 pairs, with 2 colleters at the joint of the petiole and blade, petioles 2–5 cm long, glabrate or with a mixture of very disperse trichomes, stem-like. Inflorescences congested-racemiform, extra-axillar, 1 per node, 3–5 flowers, glabrate, peduncles 1–5 cm long, pedicels 2.5–5 cm long, bracts narrowly lanceolate, 5.5–7 × 0.5–0.7 mm, glabrous, tube of the calyx absent, with 1–2 colleters per sinus, lobes narrowly lanceolate, 15–18 × 1.5–2 mm, glabrate, simple indumentum; corolla rotate, green with dark red or purple center, glabrate outside, simple indumentum, tube ca. 15 mm, lobes narrowly lanceolate, with auricles at the sinuses and the right margin possibly of white color, 30–35 × 3–3.5 mm, patent to diffuse, concave, mid basal region rugose at the center and puberulent forming a narrow band at the right margin, faucal ring a cup, 0.3–0.5 mm tall, slightly 5-lobed, densely pubescent; gynostegium a 5-lobed cup, adnate at the base of the gynostegium and corolla, 0.5–1 mm tall, erect, striate dorsally, dorsal appendages of the anthers spatulate, laminar, 0.8–1 × 1.2–1.5 mm, deflexed, apex truncate to oblique, head of the stigma pentagonal, flat, 3.5–4 mm wide, terminal appendages free and reclined on the margin of the style apex, ca. 0.5 × 1.5 mm, linear guide lanes, ca. 0.2 × 0.1 mm; corpuscle sagittate, 0.19–0.22 × 0.1–0.11 mm, dark brown, arms 0.3–0.35 × 0.14–0.15 mm, pollinia 1–1.2 × 0.5–0.6 mm. Fruit and seeds unknown.

Distribution and phenology: — Gonolobus sanmartinus is restricted to the Tropical Biology Station “Los Tuxtlas”, Veracruz, Mexico ( Fig. 2 ). It occurs in tropical montane cloud forest, in red soils rich in clay, between 1100–1200 m. It flowers in April and June. Fruits are yet to be recollected.

Conservation status: —The Los Tuxtlas region has been studied since 1987 ( Ibarra-Manríquez & Sinaca 1987) and is possibly the most widely studied in the country, with over 50000 plant data recollections ( Villaseñor et al. 2018). However, Gonolobus sanmartinus is described based only on two collections separated by 4.5 km. Its area of occupancy (AOO) ranges 8 km ² and the extent of occurrence (EOO) is 0 km². Given the continuous reduction of AOO and EOO, because already in 1986 it was calculated that approximately 84 % of the original forest area of the Los Tuxtlas reserve had been lost ( Dirzo & García 1992), and that this species has only been collected in 1954 and 2001, the category of Critically Endangered B2ab(ii) is recommended, according to the IUCN criteria (2022).

Etymology: —The specific epithet is derived from the name of the San Martín volcano, where the specimens were found.

Additional examined specimens: — MEXICO. Veracruz: Mpio. San Andrés Tuxtla, Colonia Ruiz Cortínez, ladera SE del Volcán San Martín , 18°31‘32.5“N, 95°08‘21.8“W, 1100–1200 m, 22 jun. 1997, fl., Á . Campos et al. 5274 ( MEXU!) .

Figures

FIGURE 1. Gonolobus sanmartinus. A. Plant habit with inflorescences; B. Indumentum of branch; C. Indumentum on the adaxial side of a leaf; D. Upper view of the flower; E. Base of the corolla lobes and a band of trichomes near the margin; F. Faucal ring, gynostegial corona and gynostegium; G. Detail on the faucal ring; H. Longitudinal section of the gynostegium; I. Pollinarium. A–I (Illustrated by Ericka Belén Cortez Castro from the holotype).

FIGURE 2. Gonolobus sanmartinus and G. pallidus. A-B. G. sanmartinus, A. Holotype (XAL!). B. Flower and gynostegium. C-D. G.pallidus, C. Isotype US- 03169019! (downloaded from https://ids.si.edu/ids/media_view?id=ark:/65665/m3984dd02a9d79432d9125a 32ef9c8fea7&defaultView=image_dynamic). D. Flower and gynostegium.

FIGURE 3. Distribution of Gonolobus species in the Biosphere Reserve of Los Tuxtlas and the state of Chiapas, Mexico.