Begonia sordidissima Elmer (1915: 2557) (Fig. 1)

Type:— PHILIPPINES. Mindanao Island, Province of Agusan, Cabadbaran, Mt. Urdaneta, elev. 229 m, August 1912, A.D.E. Elmer 13575 (lectotype: NY-image! [barcode 00118663], designated here; isolectotypes: B-image! [barcode B100238408], BM-image!, BISH-image! [barcode BISH1000976], BO-image! [barcode BO-1852538], E-image! [barcode E00288964], FI-image! [barcode FI014710], GH-image! [barcode 00068347], K-image! [barcode K000761030], L-image [barcode L.0625707], LY-image! [barcode LY02499090], MO-image [barcode MO-1922656], P-image! [barcode P01900778], U-image! [barcode U.0181293], US-image! [barcode 00115456].

Epipetric to terrestrial, monoecious, rhizomatous herb, up to 35 cm tall. Rhizome creeping, cylindrical, 5–8 mm in diameter, lenticellate, glabrous to sparsely hirsute, pale brownish green to green except the reddish green nodes, internode up to 1.5 cm long. Leaves alternate, spreading, up to 21 cm long, petiolate, stipulate; stipule persistent, broadly ovate, concave, 6–8 × 4–6 mm, chartaceous, keeled, glabrous except the hirsute on keel, red to reddish pale green, margin involute, apex aristate, arista 2–3 mm long; petiole terete, succulent, 13–17 cm long, 5–6 mm in diameter, densely hirsute to hirsute, green to reddish green (maroon when young); lamina asymmetric, elongate orbicular-ovate to broadly ovate, 14–16 cm long by 9–11 cm wide, subsucculent, adaxially green to pale green, glabrous, abaxially whitish to brownish green, glabrous to sparsely pubescent, margin entire to repand, base cordate, overlapping, apex obtuse to acuminate; veins palmate, with 5–7 major lateral veins, actinodromous, branching dichotomously, pale green, adaxially channeled, glabrous, abaxially protruding, pubescent. Inflorescence axillary, paniculate, protandrous, bisexual, 10–24 cm long, erect, dichotomously branching; peduncle terete, tapering towards the apex, 8.0– 18.5 cm long, 2–3 mm in diameter, succulent, sparsely hirsute, pale red to reddish pale green; rachis terete, 3–5 cm long, 1.0– 1.5 mm in diameter, glabrous to minutely glandular, pale green to reddish green; bracts persistent, broadly ovate, 3–4 × 1–2 mm, concave, green, ventrally glabrous, dorsally glandular. Staminate flower 1–2 per cincinnus; pedicel terete, erect, 8–9 mm long, 0.8–1.2 mm in diameter, succulent, glabrous to glandular (especially when immature), pale to whitish green; tepals 4, outer 2, orbicular to ovate, 5–8 × 4–8 mm, dorsoventrally glabrous (dorsally glandular when young and unopen), greenish white, margin entire, apex obtuse to rounded, inner 2, oblanceolate, 4.0–6.0 × 1.5–3.0 mm, dorsoventrally glabrous, greenish white, margin entire, apex obtuse; stamens numerous, ca. 40–55, amber, filament 0.8–1.0 mm long, anther obovoid, 1.5–2.0 mm long, apex emarginate. Pistillate flower 1 per cincinnus; pedicel erect to apically curved, terete, 7.0–9.0 × 0.8–1.0 mm, succulent, glabrous to sparsely glandular, green suffuse with red at apex; ovary 3-locular, broadly elliptic, 5–6 × 6–7 mm (wings included), 3–4 mm wide (wings excluded), glabrous to occasionally sparsely glandular, green suffuse with brick red, apex acute to subacute, wings 3, equal, apex obtuse, placentation axile, bilamellate; tepals 4, outer 2, ovate, 6.5–7.3 × 3.8–4.2 mm, convex, dorsoventrally glabrous, margin entire, revolute, apex rounded, inner 2, narrowly obovate, 5.0–6.0 × 2.8–3.5 mm, concave, dorsoventrally glabrous, margin entire, apex rounded; style 3, 3.0– 3.5 mm long, lemon green, bifid, apically forked; stigma spirally twisted, papillose all around. Fruit up to 1.5 cm long, reclinate; pedicel terete, 6.0– 6.5 mm long, 0.8–1.0 mm in diameter, glabrous, apically strongly recurved, green suffuse with brick red; capsule broadly elliptic, 5–7 × 6–8 mm (wings included), 4–5 mm wide (wings excluded), green suffuse with pale brick red to green (brown as it dries up), glabrous, apex acute, wings 3, unequal, apex rounded.

Distribution: —Endemic to Mindanao Island where it has so far only been found in Cabadbaran and Butuan City (Agusan del Norte), Prosperidad (Agusan del Sur) and Claver (Surigao del Norte) of Caraga Region, northeastern Mindanao Island (Fig. 2). A specimen from Surigao matches this species but was excluded from the distribution map due to the lack of precise locality data for georeferencing. The specimen A.D.E. Elmer 15755 from Mt. Bulusan of Sorsogon, Luzon Island, was previously misidentified as B. sordidissima but is now confirmed to represent B. biliranensis Merr (1915: 46).

Habitat: —Found growing in dense forested ravines and on slopes, typically thriving in deep humus or spreading across humus-covered rocks with loose soil and boulders near cliff edges, at elevations ranging from 170–229 m (Fig. 3).

Phenology: —Observed flowering and fruiting from June to November.

Proposed conservation status: —At present, it is only known from four localities with less than 50 mature individuals observed and giving an estimated EOO of 1,565.095 km 2 and AOO of 16 km 2 when calculated using GeoCAT system with 2 km defined cell-width (Bachman et al. 2011). The species is relatively rare and occurs in unprotected areas, making it particularly vulnerable to anthropogenic disturbances such as agricultural land expansion and tourism. Following the red list criteria of the IUCN Standards and Petitions Subcommittee (2024), we herein provisionally classified as ‘Endangered’ (EN B1[i,ii,iv],2[i,ii,iv]).

Additional specimens examined: — Philippines, Mindanao Island, Agusan del Norte, Butuan City, Brgy. Sumile, elev. 207 m, 8.83841142 ° N, 125.62622068 ° E, 18 April 2024, A.A. Along with MAK Naive 204 (CLP, HNUL); ibid., 7 November 2024, A.A. Along with J.J.J. Ruales & MAK Naive 199 (CLP, HNUL); Agusan del Sur, Prosperidad, Brgy. Mabuhay, Bega Falls, elev. 170 m, 8.69944°N, 125.97528°E, 22 June 2024, R.R.E. Rozano & MAK Naive 201 (CLP).

Notes: — Hughes et al. (2010) noted significant morphological distinction in Begonia sordidissima from B. mindorensis but highlighted the need for further study due to poor condition of available specimens. Through examination of the type material, recently collected specimens, and the protologue, we confirm that B. sordidissima is readily distinguished from B. mindorensis by the following characters: 6–8 mm long (vs. 10 mm long) stipules, subsucculent, elongate orbicular-ovate to broadly ovate (vs. chartaceous, ovate-lanceolate) leaves with 5–7 (vs. 7–9) lateral nerves, up to 24 cm long (vs. up to 35 cm long) inflorescence, sparsely hirsute (vs. ultimately glabrous) peduncle, occasionally sparsely glandular (vs. consistently glabrous) rachis, dorsally glandular (vs. glabrous) immature outer staminate tepals. In addition, B. mindorensis has highly persistent bracts at the base of each inflorescence branch and unequal ovary wings with an acute dorsal wing, while B. sordidissima exhibit caducous bracts and equal, obtuse ovary wings. Elmer (1915) described B. sordidissima based on his specimens collected in Mt. Urdaneta of Agusan Province in August 1912. Among the 15 syntypes located, we designate the specimen at NY as the lectotype due to its wellpreserved state with both vegetative and reproductive parts, supplemented by Elmer’s original field notes. The species is referred to as ‘ calohoglohog ’ by the Manobos in the type locality (Elmer 1915). The Manobo (“river people”) are one of the local peoples and minorities inhabiting several areas in Mindanao.

Morphological variability was observed in both vegetative and reproductive parts, including the indumentum of the rhizome, petiole and inflorescence. Leaf shape also exhibited variation, notably, some populations displayed obtuse leaf apices rather than the typical which is acuminate. Among Mindanao Begonia sect. Baryandra species, the species can be mistaken as B. acuminatissima Merrill (1911: 395). However, B. sordidissima can be easily distinguished by having densely hirsute (vs. with few, scattered hairs or ultimately glabrous) petiole, orbicularly ovate to broadly ovate leaves with overlapping and cordate base (vs. obliquely oblong-ovate or narrowly ovate leaves with broadly sinuate to slightly cordate base), longer than the leaves (vs. about as long as the leaves) inflorescence and capsule with unequal (vs. capsule with subequal) wings. It is also similar to B. longiscapa, however, B. sordidissima can be easily distinguished by having leaves with 5–7 (vs. 9) major lateral veins, up to 24 cm long (vs. up to 35 cm long) inflorescence, persistent and glandular (vs. caducous and glabrous) bracts, pistillate flower with 7–9 mm long (vs. 10–20 mm long) pedicel, fruit with acute base and apex (vs. retuse), and unequal (vs. subequal) ovary wings.