Begonia ostulensis Martínez & Ramos, 2022

Martínez-Gordillo, Martha & Ramos-Ordoñez, María Felix, 2022, Begonia ostulensis (Begoniaceae), a new species from Michoacán, Mexico, Phytotaxa 543 (1), pp. 89-94 : 89-93

Begonia ostulensis Martínez & Ramos sp. nov.

§ Knesebeckia ( Fig. 1 ).

Similar to B. monophylla Pav. ex A.DC. (1859:121) , but differs in having orbicular, peltate leaves (vs. suborbicular to elliptic reniform or broadly ovate, basifixed leaves with a cordate base), that are glabrous on the lower and upper surfaces (vs. sparsely pubescent), with a lobed, double-dentate, non-ciliate margin (vs. with incised-dentate, ciliate margin, occasionally lobed); stipules fugacious (vs. persistent); inflorescence terminal (vs. axillary).

Type: — MEXICO: Michoacán de Ocampo, Municipality of Aquila, 2.4 km NW to Santa María Ostula, road to Potrerito , 18°31’14.34” N, 103°29’28.29” W, 827 m, 16 Jul 2021, O.D.Calderón 1 (holotype FCME, isotype MEXU) .

Monoecious herbs, perennial, acaulescent, developing annually from underground tubers; tuber globose to obovoid, 2–5 × 3–7 mm, covered by yellowish-white scales. Leaves solitary, simple, green, orbicular, 2.1–11 cm in diameter, peltate, margin lobed and double-dentate, non-ciliate, lower surface glabrous, upper surface glabrous, venation 7–10- palmatinerved, conspicuous; petiole 0.5–2.7 cm, with a trichome ring at the petiole-blade union, trichomes 0.4–0.5 mm, simple; stipules fugacious. Inflorescence terminal, solitary, arising from the centre of the leaf, 3.5–18 cm long, racemose, bisexual, 1(–2) flowers per node; pistillate flowers 1–6, in the proximal nodes, staminate flowers 1–2(–4), generally in the distal nodes; peduncle 3.2–10 cm, glabrous; bracts in pairs, 2.5–8.3 × 2.5–9 mm, persistent, broadly obovate, amplexicaul, margin fimbriate, glabrous. Staminate flower with pedicels 0.7–8 mm long, glabrous; tepals 4, outer 2 white, sometimes blushed pink at the apex, 3.8–4 × 3.3–3.6 mm, ovate, white, apically acute to rounded, glabrous; inner 2 white, 4–5 × 2–2.4 mm, oblong, apically rounded to acute, margin entire, glabrous; receptacle flat; androecium monadelphous, actinomorphic, 2.1–2.7 mm, filaments 1.5–2.3 mm, anthers turbinate, 0.4–0.6 × 0.4–0.6 mm, shorter than the filament, dehiscence longitudinal. Pistillate flowers with pedicels 0.4–2.7 mm long, glabrous, perianth with 5 tepals, in 2 verticils, subequal, 4–4.5 × 3–3.5 mm, ovate, apically acute, margin entire, glabrous, white; receptacle flat; ovary trilocular with bipartite placentae, glabrous, alate, wings 3, unequal, styles 3, simple, joined only at the base, persistent in the fruit, stigmas lunate, covered by stigmatic papillae. Capsules with pedicels 0.5–2.4 mm, slightly pendulous, tepals deciduous; locular chamber ellipsoid; wings 3, the primary wing asymmetrically triangular, 0.8–1.3 × 0.6–1 cm, glabrous, the other two smaller, dimidiate. Seeds ellipsoid, light brown.

Additional specimens examined (paratypes): — MEXICO: Michoacán, Aquila , 2.8 km NW of Santa María Ostula, way to Palmita , 759 m, 18°31’04.8”N, 103°29’55.3”W, 17 Jul 2021, Calderón OD 2–11 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 604 m, 18°31’10.47”N, 103°29’22.5”W, 07 Sep 2021, Villalobos D 1 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 788 m, 18°31’11.47”N, 103°29’22.5”W, 07 Sep 2021, Villalobos D 2 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 791 m, 18°31’10.98”N, 103°29’22.38”W, 07 Sep 2021, Villalobos D 3 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 782 m, 18°31’11.04”N, 103°29’22.24”W, 07 Sep 2021, Villalobos D 4 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 785 m, 18°31’10.95”N, 103°29’21.81”W, 07 Sep 2021, Villalobos D 5 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 776 m, 18°31’10.78”N, 103°29’21.42”W, 07 Sep 2021, Villalobos D 6 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 604 m, 18°31’10.47”N, 103°29’22.5”W, 18 Nov 2021, Villalobos D 7 (FCME, MEXU) ; 2.2 km NW of Santa María Ostula, way to Potrerito , 788 m, 18°31’11.47”N, 103°29’22.5”W, 18 Nov 2021, Villalobos D 8 (FCME, MEXU) .

Etymology:—The name honors the type locality: Santa María Ostula, Aquila Municipality, Michoacan State, Mexico.

Distribution and habitat: —The species is only known from the type locality, on limestone rock ridges. Due to its size it is an inconspicuous species. It grows in cracks or lateral cavities of rocks ( Fig. 2 ), never on the surface exposed to the sun, which makes it difficult to collect the tubers. Its life cycle is constrained by the rainy season (June to October); the leaf is observed in the first week of July, flowering occurs from July to September, in the month of November no flowers are found, only senescent leaves with dry fruits are observed. The type of vegetation is tropical deciduous forest, at elevations ranging from 604 to 828 m above sea level. It has been found in sites inhabited by Beiselia mexicana Forman (Burseraceae) , another species endemic to the municipality of Aquila.

Taxonomic comments:— This species is placed within B. section Knesebeckia , a section originally defined as a genus showing its filaments joined at the base, forming a column, anthers obovate, stigmas bifid, dilated at the base and placentas divided in two branches (Klotszch 1854), but which was determined to be polyphyletic in later molecular studies ( Moonlight et al., 2018); this section is distributed in the Americas, with one of its main centers of diversity in Mexico. Morphologically, the new species is at first sight similar to Begonia monophylla Pav. ex de Candolle (1859:121) , which is distributed in the states of Mexico, Colima, Michoacán, Guerrero and Morelos ( Fig. 3 ), since it has one conspicuous, solitary leaf lying on the ground, but it is easily distinguished by the orbicular, peltate leaves and several other characters ( Table 1 ). It grows in rocky zones, generally with the tubers emerging through crevices in the rocks. B. monophylla is found in dry deciduous woodlands, oak forest, grassy summit slopes, steep ravines and shaded cliff-faces and talus slopes on calcareous or gypseous rocks ( Burt-Utley and McVaugh, 2001); it has quite a variable leaf size as it depends on the tuber size and environmental conditions ( Burt-Utley and McVaugh, 2001).

Figures

FIGURE 1. Begonia ostulensis. A: Habit. B, B’: Pistillate flower (face and side views). C, C’: Staminate flower (face and side view). D: Ovary. E: Styles and stigmas. F: Cross section of the ovary. G: Fruit. H: Androecium. I: Stamen. J: Seed. K: Bract. L: Trichome ring. M: Tuber. Based on live plants in Santa María Ostula, by D. López-Guerrero and M.F. Ramos-Ordoñez.

FIGURE 2. Begonia ostulensis in its habitat. Photographs by D. López-Guerrero.

FIGURE 3. Distribution map of Begonia ostulensis and B. monophylla in Mexico. B. monophylla distribution data taken from GBIF (2022), elevation range was obtained from INEGI (2013).