Begonia nosymangabensis Scherber. & Duruiss., 2017

Scherberich, David & Duruisseau, Jacky, 2017, Two new species of Begonia sect. Erminea (Begoniaceae) from Nosy Mangabe in Madagascar, Candollea 72 (2), pp. 257-263 : 258-261

Begonia nosymangabensis Scherber. & Duruiss. , spec. nova ( Fig. 1 , 3 E-F).

Typus: [ MADAGASCAR. Prov. Toamasina]: Plant in cultivation in Lyon Botanical Garden under n° 100651, originally collected by H. Laporte in 1998 in Nosy Mangabe , 10.V.2016, Scherberich 1132 (holo-: LYJB!; iso-: G!, P!, TAN!) .

Begonia nosymangabensis Scherber. & Duruiss. can be compared with B. keraudreniae Bosser but differs by the larger size with more leaves (5-25 vs 1-3) which are longer and narrower (7-15 cm vs 3.5-6.5 cm long), more deeply incised, without spiculiform hairs adaxially and a longer stem (2-7 cm vs 1-3 cm). It could also be compared to B. nana L’Hér. and B. lemurica Keraudren but differs from both by the presence of a stem, from the former by the deeply lacerate-incised blades, and from the later by the larger lamina (5-9 × 2-3.5 cm vs 3.5 × 3 cm) with more primary lateral veins (3-4 vs 1 pair) and a higher number of stamens (10-14 vs 8).

Tuberous perennial lithophytic herb with short upright clustered stems. Tuber small, 20-30 mm, irregular, strongly adherent. Stem herbaceous, 2-7 cm, red; internodes 0.6-1.5 cm. Stipules persistent, the margins entire. Leaves 5-25, alternate, sometimes pseudo-distichous, straight; petiole 2-4.7 cm long, 1.5-2 mm diam., cylindrical, slightly flattened on adaxial side, glabrous, red; blade 5-9 × 2-3.5 cm, symmetric to slightly asymmetric, oblanceolate to obtrullate, deeply lacerate-incised, mucronulate in upper 2/3, the base acute, entire, the apex narrowly acuminate, serrate, the margins revolute, light green and semiglossy to subvelvety adaxially, paler and semiglossy abaxially; midrib and primary lateral veins slightly raised adaxially, very prominently raised and pale red abaxially; primary lateral veins 3-4 per side, arising at an angle of 10-20°. Inflorescence a dichasial cyme, axillary, bearing 5-6 flowers at summit, bisexual, protandrous, with basal male flowers and a solitary distal female flower; inflorescence axis 5.5-9.5 cm long, 1.2- 1.6 mm diam.; bracts present at anthesis, eventually caducous, lanceolate, 3-4 × 1.5-2.5 mm; bracteole absent; perianth segments pink, paler at the apex. Male flower perianth segments 4, free, peduncle 9-12 mm; outer perianth segments elliptic-obovate, apex obtuse, 8.4-9 × 5.5-7 mm; inner perianth segments oblanceolate 8-8.5 × 3-3.5 mm, paler; stamens (9-)10-14 (-17); androecium zygomorphic; filaments fused at the base into a column 0.5-0.7 mm long; free part 0.8-0.9 mm; anthers longer than filament, oblong, 1.4-1.7 mm, dehiscent through lateral longitudinal slits; connective not extended. Female flower perianth segments (5-)6, free; peduncle 11-13 mm; outer perianth segments oblanceolate-obovate, apex obtuse, 9-10.5 × 3.6-6.4 mm; inner perianth segments oblanceolate, 8.5-11 × 3.5-4 mm, paler; ovary 3-winged, unequal, with one wing conspicuously larger than the two others, red-brown, composed of 3 locules; placentae septal, bi-lamellate; ovules numerous, white; styles 3, fused halfway, bifid, white to pale yellow, persistent in fruit; stigma reniform, in a band, yellow; Fruit a 3-winged dry capsule, nodding, the wings unequal. Seeds ovoid, 0.4-0.5 × 0.2 mm, tegument reticulate.

Distribution and ecology. – Known only from the type collection in Nosy Mangabe, Madagascar, where it grows on mossy granite boulders in stream beds, at low elevation. It has been found growing in association with B. erminea L’Hér. and a suspected natural hybrid between both has been observed. Flowering in cultivation has been observed most of the year as long as humid and warm conditions are provided.

Conservation status. – The island of Nosy Mangabe is a protected area, with a surface of 5.2 km 2 and is included in the Masoala National Park. As B. nosymangabensis is restricted to this small island, it has a very small area of occupancy. As such, eco-tourism and illegal collectors could have a rapid negative impact on the conservation of this new species. In regards that the new species has a population with a very restricted area of occupancy (<20 km 2), the conservation status as “Vulnerable” [VU D2] is proposed following the IUCN Red List Categories and Criteria ( IUCN, 2012).

Notes. – Some herbarium specimens from Nosy Mangabe, which were initially thought to represent another undescribed species, could in fact be B. nosymangabensis although they have a slightly different morphology. They have longer stems without basal leaves and the blades are narrower with more profound lobes (Schatz 1904, MO, P, TAN and Du Puy MB147, K, TAN). Although B. nosymangabensis has been in cultivation for 15 years and has been reproduced by seeds occasionally, no plant has ever shown the characteristics of these specimens. B. nosymangabensis belongs to section Erminea . The male and female flowers with 4 and 6 tepals respectively, the presence of a staminal column and the 3 bifid styles are typical of that section.

Figures

Fig. 1. – Begonia nosymangabensis Scherber. & Duruiss. A. Habit; B. Leaf, adaxial side; C. Male flower, front view; D. Male flower, side view; E. Androecium; F. Female flower, face view; G. Female flower, side view; H. Styles and stigmas; I. Ovary; J. Ovary cross-section. [Scherberich 1132, LYJB] [Drawing: Vanessa Damianthe]

Fig. 3. – Begonia pteridoides Scherber. & Duruiss. (A-D) and Begonia nosymangabensis Scherber. & Duruiss. (E-F). A. Habit in cultivation; B. Stem; C. Leaf, abaxial side; D. Young plant showing juvenile leaves; E. Habit in cultivation; F. Stem. [Photos: A-D, F: David Scherberich; E: Evelyne Bouquet]