Begonia fluvialis M.Hughes, 2015

Hughes, Mark, Girmansyah, Deden & Ardi, Wisnu Handoyo, 2015, Further discoveries in the ever-expanding genus Begonia (Begoniaceae): fifteen new species from Sumatra, European Journal of Taxonomy 167, pp. 1-40 : 9-12

Begonia fluvialis M.Hughes sp. nov. § Reichenheimia

urn:lsid:ipni.org:names:77151639-1

Figs 3 , 4

Diagnosis

A rheophytically adapted sister species closely allied to B. sublobata Jack ( Jack 1822) , from which it differs in its smaller size (<20 cm high, not 20–30 cm high) and its smaller, narrower leaves (8–15 × 1.5–5.5 cm, not c. 12 × 12 cm). Other distinctive characters are the petioles being triangular in cross section, and the cuneate lamina with up to 3 apical lobes. See also the diagnosis for B. lilliputana below for a comparison with that species.

Etymology

The epithet is derived from the Latin fluvius (river) and means “of the river”.

Type

SUMATRA: West Sumatra, Sungai Pinang, Batang Ayer Manjuto, 350 m, 12 Aug. 2010, Girmansyah, Hughes & Nurainas DEDEN 1489 (holo-: BO; iso-: E).

Additional material

SUMATRA: West Sumatra, Sungai Pinang, Batang Ayer Manjuto, 350 m, 12 Aug. 2010, Girmansyah, Hughes & Nurainas DEDEN 1490 ( BO, E).

Description

Repent acaulescent lithophytic riverine herb, 10–20 cm tall; stem rhizomatous, internodes c. 0.5 cm long. Stipules persistent, with a few stiff hairs on the keel or glabrous, 10 mm long, lanceolate, with a filiform extension at the apex. Leaves: petiole 6–10 cm long, triangular in cross section, with sparse minute glandular hairs when young rapidly becoming glabrous with age, with a semicircle of 3–6 stiff red bristles at the apex, bristles 2–4 mm long; lamina, cuneate with 1–3 apical triangular lobes, symmetric, 8–15 × 1.5–5.5 cm, basifixed, base minutely cordate and slightly auriculate, upper surface light green, glabrous on both sides, venation palmate-pinnate; margin sub entire to shallowly dentate, with recurved stiff teeth at the end of the veins, apex acuminate. Inflorescences axillary, total length 15–18 cm, cymose, branching 3–4 times, 12–15 flowered, bisexual, protandrous; primary peduncle 13–16 cm; bracts caducous, sub-orbicular, 2–3 mm long, margin entire. Male flowers: pedicel red, c. 8 mm long, glabrous; tepals 4; outer tepals broad ovate to sub orbicular, fleshy, 6–7 × 5–6 mm, pale pink, glabrous, margin with a distinct rim; inner tepals elliptic, 4 × 2 mm, white; androecium pale yellow, globose; stamens c. 80; filaments, subequal, 0.5 mm long, fused at the base into a 0.5 mm long column; anther about as long as the filament, elliptic-obtriangular, 0.5 mm long, connective slightly retuse, dehiscing through slits about half the length of the anther, slits placed laterally. Female flowers: pedicel c. 5 mm long; ovary green, glabrous, 5 × 12 mm including the wings; capsule orbicular, 4 mm in diameter, 3 locular, placentae entire; wings triangular, c. 4 mm long; tepals 2–3; outer tepals 2, same as male flower; inner tepal 0–1, same as male flower; stigmas 3, shallowly Y-shaped, surface tightly twice spirally twisted, greenish yellow. Fruit recurved on a 8–12 mm long pedicel; rounded at base; capsule orbicular, 5–6 mm in diameter; total size 8 × 15 mm including the wings; wings equal to subequal, 5 × 7 mm, apex obtuse.

Distribution and habitat

Only known from two collections from neighbouring streams near Sungai Pinang in West Sumatra ( Fig. 4 ). B. fluvialis grows on moss covered rocks at the side of and emerging from streams running down the mountainside.

Conservation status

The forest habitat of the type locality seems to be well managed and under some community protection. However the lack of a formally gazetted protected area and the potential for landslides to encroach the streamside habitat means B. fluvialis should be considered Vulnerable under criterion VUD2 of IUCN (2012).

Figures

Fig. 3. Begonia fluvialis M.Hughes sp. nov. A. Habit. B. Inflorescence in male phase. C. Two female flowers. D. Petiole apex showing three red bristles. All photographs from Batang Ayer Manjuto of the type Girmansyah et al. DEDEN1489. Scale bars on insets = 1 cm.

Fig. 4. Map of Sumatra showing the full known species distributions based on collection localities. Each point may represent more than one collection.