Tigridia nanchititlensis Aarón Rodr. & D.Szeszko, 2020

Rodríguez, Aarón, Szeszko, Dennis & Munguía-Lino, Guadalupe, 2020, The species of Tigrideae (Iridaceae) in the Sierra of Nanchititla, State of México, Mexico, and description of the new species Tigridia nanchititlensis, Phytotaxa 446 (5), pp. 268-280 : 274-276

Tigridia nanchititlensis Aarón Rodr. & D.Szeszko sp. nov. ( Figs. 2 and 3 )

Tigridia nanchititlensis is a rupicolous and pendulous geophyte belonging to T. subgen. Hydrotaenia Lindley (1838: 69) . It is distinguished from other related species by having 2–3 basal leaves, campanulate flowers, purple to red-purple tepals, a concolorous and inverted V-shaped nectary, and pedicels involute in the fruit.

Type: — MEXICO. State of México: municipality of Luvianos, Torrecillas , km 15 road El Estanco-Cañadas de Nanchititla , 18°52ʼ10.19ˮN, 100°19ʼ53.76ˮW, 1877 m, 27.VII.2010, A. Rodríguez et al. 6049 (holotype IBUG; isotypes CHAPA, CIIDIR, ENCB, IEB, MEXU, MO, NY, UAMIZ) .

Description: —Bulbous, perennial, rupicolous, and pendulous herb, 10–50 cm tall, glabrous; bulb ovoid, 1–5 × 0.5– 3.5 cm, the outer tunics thin, pale brown; scape unbranched or bearing one or two branches, 13–36 cm tall; basal leaves 2–3, linear-lanceolate, plicate, 15–110 × 0.1–3 cm, longer than the scape at anthesis; cauline leaves 1, linear-lanceolate, plicate, 10–23 × 0.2–1.4 cm; rhipidium with subequal spathe valves, 1.5–3 × 0.3–1.2 cm; peduncle linear, 2.1–8.7 cm long; pedicels linear, 2.5–5 cm long, involute in fruit; flowers 2–6 per rhipidium, erect, 2–3 cm wide; tepals connivent into a campanulate form; outer tepals obovate, attenuate, obtuse, 1.2–1.5 × 0.9–1 cm; inner tepals ovate, unguiculate, mucronate, 0.8–1 × 0.4–0.6 cm; tepal color varies from purple (purple group 76D, Royal Horticultural Society 2015) to red-purple (red-purple group 72B, Royal Horticultural Society 2015); nectary a broad inverted V-shaped band, 4 mm wide, concolorous; filaments connate, 2 mm long; anthers adpressed, 5 mm long; ovary clavate, 3–4 × 1.5 mm; style branches 2 mm long, bifid; mature capsule clavate, 1.2–1.5 cm × 5–6 mm; seeds ovoid, 2.5 × 1.5 mm.

Etymology: —The specific epithet refers to the Sierra of Nanchititla, where this species grows.

Distribution, ecology and phenology: — Tigridia nanchititlensis is only known from the Sierra of Nanchititla in the State of México ( Fig. 1 ). It has been found between 1845–1927 m a.s.l., growing on vertical walls of high rocky outcrops in OPF. The forest comprises mainly xerophilous trees adapted to growing in highly mineralized, poornutrient soils and capable of withstanding acute seasonal drought. Some of the species are Quercus crassipes Bonpl. in Humboldt & Bonpland (1809: 37), Q. glaucescens Bonpl. in Humboldt & Bonpland (1809: 29), Q. magnoliifolia Née (1801: 268) , Q. urbani Trelease (1921: 32) , Pinus oocarpa Schiede ex Schlechtendal (1838: 491) , P. pringlei Shaw in Sargent (1905: 211), and Arbutus xalapensis Kunth in Bonpland et al. (1818: 279).

Together with Tigridia nanchititlensis , we found Bletia concolor Dressler (1968: 183) , B. gracilis Loddiges et al. (1833: 1977) , B. macristhmochila Greenman (1897: 297) , Calochortus spatulatus Watson (1879: 267) , Cheilanthes aurantiaca ( Cavanilles 1802: 266) Moore (1857: 38) , Dioscorea multinervis Bentham (1839: 52) , Fuchsia fulgens Candolle (1828: 39) , and Pellaea ternifolia ( Cavanilles 1802: 266) Link (1841: 59) . Other components of the plant community belong to Agave sp. , Habenaria sp. , Ipomoea sp. , Lophospermum sp. , Mammillaria sp. , Marchantia sp. , Oxalis sp. , Pinguicula sp. , Pitcairnia sp. , Sedum sp. , Tillandsia sp. , and mosses. Tigridia nanchititlensis flowers from June to August. The fruits mature in September.

Tigridia nanchititlensis exhibits several traits consistent with the hummingbird pollination syndrome. It has red-purple, inodorous and diurnal flowers. The plants grow on vertical rock walls in a manner that only hovering pollinators can reach them. The flower is tubular and oriented perpendicularly to the rock surface; and the anthers of the flowers are in the same horizontal plane as the tepals. While visiting the type locality, we were unable to obtain visual confirmation of hummingbird visits to T. nanchititlensis plants, but we did observe many hummingbirds flying up and down the rock faces visiting other flowers of Oxalis sp. and Pitcairnia sp. Thus, we think that it is probable that some plants of T. nanchititlensis are pollinated by hummingbirds.

Conservation assessment: — Tigridia nanchititlensis is represented by four nuclei separated on average by 730 m ( Fig. 1 ). Based on minimum convex polygon and cells of 2 × 2 Km, the Extent of Occurrence (EOO) was 0.221 Km 2 and 4 Km 2 for the Area of Occupancy (AOO). Following the IUCN (2019) criteria, the EOO and AOO values were less than 100 Km 2 and 10 Km 2, respectively. Therefore, it falls within the Critically Endangered category (CR, B1 and B2).

Additional material examined (paratypes): — MEXICO. Estado de México: Luvianos, Torrecillas, Sierra de Nanchititla , 18°52ʼ7ˮN, 100°19ʼ30.7ˮW, 1900 m, 20.IX.2008, A. Rodríguez & D. Szeszko 5624 ( CHAPA, CIIDIR, ENCB, IBUG, IEB, MEXU, MO, NY, UAMIZ, US, WI) ; Luvianos, en la brecha a Torrecillas , 18°52ʼ30.4ˮN, 100°19ʼ46.6ˮW, 1927 m, 4.VII.2012, G. Munguía-Lino & L.M. Vázquez-García 186 ( IBUG) ; Luvianos, Sierra de Nanchititla, aproximadamente 1 km al SO del paraje conocido como Torrecillas , 18°52ʼ27.5ˮN, 100°19ʼ45.1ˮW, 1845 m, 20.VI.2013, G. Munguía-Lino & L.M. Vázquez-García 253 ( IBUG) .

Taxonomic remarks: — Tigridia nanchititlensis and T. pugana Rodríguez & Ortiz-Catedral (2006: 60) are unique among other species in the genus due to their habit of colonizing the vertical rock walls of giant monoliths. However, T. pugana has bulbils in the axils of the cauline leaves ( Rodríguez & Ortiz-Catedral 2001), absent in T. nanchititlensis . In T. nanchititlensis , the rupicolous plants are almost entirely pendulous, except for the peduncle and pedicels which extend horizontally. During carpogenesis, the pedicels exhibit a gravitropic response and elevate the ovaries skyward to allow the seed capsules to develop in an upright position. This characteristic is easily seen in herbarium specimens and can be used to conclusively identify this species ( Fig. 3H ).

Morphologically, Tigridia nanchititlensis resembles T. meleagris ( Table 1). They share campanulate flowers and exposed nectaries, but they differ in their position, as well as the color and arrangement of the nectary. Tigridia meleagris has nodding flowers whereas T. nanchititlensis extends its flowers horizontally. In T. meleagris , the nectary has an inverted V-form with the same width all the way across, and the tissue behind the nectary is yellow. In contrast, in T. nanchititlensis both ends of the nectary are wider than the central part, and its surface is white. Also, T. meleagris has a mucro between the style arms, absent in T. nanchititlensis . Finally, T. nanchititlensis produces 2–3 basal leaves, lacking in T. meleagris .

Tigridia nanchititlensis and T. meleagris grow sympatrically in the Sierra of Nanchititla. We collected specimens of both species within close proximity of each other in OPF. However, T. meleagris is a terrestrial and erect plant, whereas T. nanchititlensis is strictly rupicolous and pendulous ( Fig. 2 ).

*indicates species endemic to State of México.

Figures

FIGURE 1. Distribution map of the Tigrideae in the Sierra of Nanchititla, State of México.

FIGURE 2. Tigridia nanchititlensis. A–B. Habitat. C–D. Flower lateral and front view. E. Habit. F. Fruits. Photographs: Aarón Rodríguez.

FIGURE 3. Tigridia nanchititlensis. A. Habit. B. Bulb. C–D. Flower front and lateral view. E. Flower dissection. F. Style. G. Stamens. H. Fruits. Illustrated by Ericka Belén Cortez Castro based on type material (A. Rodríguez et al. 6049).