Begonia egamii D. Borah, Taram & M. Hughes

Borah, Dipankar, Taram, Momang & Hughes, Mark, 2023, Begonia egamii (Begoniaceae), a remarkable new species from Arunachal Pradesh, India, Candollea 78 (2), pp. 147-151 : 147-151

Begonia egamii D. Borah, Taram & M. Hughes , sp. nov. ( Fig. 1 , 2 ).

Holotypus: INDIA. Arunachal Pradesh: Leparada, Basar, EB Project Nature , 27 '35"N 94'43"E, 1000 m, 4.I.2023, Taram & Borah 10023 ( CAL!).

Begonia egamii D. Borah, Taram & M. Hughes has a very unusual combination of characters, making it hard to find a close ally for taxonomic comparison. It shares some characters with B. tamdaoensis C.I Peng such as having hispid hairs on the tepals and ovary and a zygomorphic androecium, but differs in having leaves rugulose above (vs. smooth), two stigmas (vs. three), and anthers retuse at the apex (vs. with an extended connective).

Creeping herb, 15 – 28 cm long, strigose; rhizome 5 –10 × 1 –1.5 cm, internodes very short at base, becoming a creeping stem toward apex with internodes 1– 4 cm long, mixed with more congested internodes so leaves can appear crowded together, stipules triangular to elliptic-ovate, 1 –1.6 × 0.8–1.2 cm, glabrous adaxially, pubescent abaxially, margin ciliate, apex shortly acuminate. Stem decumbent, 8 –22 × 0.3–0.5 cm, rooting at nodes, indumentum strigose (trichomes c. 5 mm long), red. Leaves appearing clustered when internodes are close together, on 6–20 × 0.2–0.3 cm petioles; lamina elliptic-ovate, 8–30 × 6–18 cm, rugulose, apex acute to shortly acuminate, base cordate with lobes overlapping, margin subentire, crenate, or serrate, ciliate, densely strigose, veins palmate, 7–9. Inflorescence axillary, cymose; peduncles strigose, primary 7.3–20 cm long, secondary 1.3–7.5 cm long, tertiary 0.5–4.5 cm long; bracts lanceolate to elliptic-ovate, 0.5–1 × 0.3 –0.6 cm, acute, entire, pubescent, with a pedicel 1 –2 cm long. Staminate flower with 4 tepals; outer tepals 2, broadly ovate to orbicular, 1.3–2 × 1–1.5 cm, glabrous inside, pubescent outside, pink; inner tepals 2, ovate to elliptic ovate, 1 – 1.3 × 0.5– 0.7 cm, glabrescent outside, glabrous inside, pinkish white; stamens 30– 60, anthers basifixed, elliptic-obovate, c. 2 mm long, connective retuse, filament c. 1.5 mm long, fused at base into a stout column; pedicel 2.5–4 cm long, strigose. Pistillate flower with 5 tepals, unequal, elliptic ovate to broadly ovate, 1–1.3 × 0.9–1.2 cm, strigose outside, glabrous inside, pink; pistil c. 2– 3 mm long, styles 2, c. 1 mm long, persistent, stigma papillose, yellow, ovary 2-locular, placentae bifid; pedicel 1–2 cm long, strigose. Capsule 1.2–1.5 cm long, densely strigose, with 1 oblong central wing and 2 shorter obtuse lateral wings, central wing 1–2 × 0.8–1 cm, lateral wings 1–1.2 × 0.3–0.5 cm.

Etymology. – The species is named after Shri. Egam Basar, a dedicated plant grower who first discovered the species in Leparada District of Arunachal Pradesh, India.

Distribution, ecology and phenology. – Begonia egamii is known only from the type locality in the EB Project Nature reserve area, Arunachal Pradesh, northeastern India. This reserve area is spread over 100 hectares dedicated to safeguard the native and threatened plant species of Arunachal Pradesh. It was found growing in two different habitat types: (1) gregariously in a recently cleared patch fully exposed to sunlight along with Dicranopteris linearis (Burm. f.) Underw. , Pteridium aquilinum (L.) Kuhn, Pseudodissochaeta assamica (C.B. Clarke) Nayar, Dimetia scandens (Roxb.) R.J. Wang , Carex sp. ; (2) on moist shady cliff faces in association with Henckelia adenocalyx (Chatterjee) D.J. Middleton & Mich. Möller, Begonia handelii Irmsch., Hydrocotyle himalaica P.K. Mukh. , Rhynchotechum parviflorum Blume, Boeica fulva C.B. Clarke , Alpinia sp. , along with mosses and liverworts.

Flowers from November to December, fruiting from December to January.

Notes. – Although the pistillate flowers with two stigmas, two-locular ovaries with axile and bifid placentae conform well with Begonia sect. Platycentrum , the asymmetric androecium is unusual for the section ( Fig. 2C ). The elongate creeping habit is also unusual; the geographically closest species with the same habit is B. repenticaulis Irmsch. from Yunnan, which considerably differs from B. egamii in having acutely lobed leaves. The unusual combination of characters suggests that the species may represent an isolated lineage. For the time being, the sectional placement of the new species remains undefinied awaiting further research.

In combination with several other recent discoveries, this new species confirms the status of the montane forests of northeastern India as a region of immense floristic diversity and endemism. It also highlights the utility of baseline regional taxonomic revisions in supporting and stimulating further taxonomic work.

Figures

Fig. 1. – Begonia egamii D. Borah, Taram & M. Hughes.A. Habit; B. Adaxial leaf surface; C. Abaxial leaf surface; D. Stipule; E. Staminate flower (inner view); F. Staminate flower (outer view); G–H. Outer tepals of a staminate flower; I–J. Inner tepals of a staminate flower; K. Style; L. Pistillate flower; M. Fruit; N. Cross section of a fruit showing locules. [Photos: D. Borah & E. Basar]

Fig.2.– Begonia egamii D. Borah, Taram & M. Hughes. A, B. Habitat; C. Detail of staminate flowers showing the unusual asymmetric androecium. [Photos: D. Borah & E. Basar]