Begonia viscosa
Begonia viscosa Aver. et H.Q. Nguyen
Species Information
Classification
Described from central Laos, Begonia viscosa is an undershrub belonging to Sect. Diploclinium?.
Distribution
This species is native to central Laos, specifically in Vientiane province, Vang Vieng district, in the vicinity of Vang Vieng town, around point 18°54’58”N 102°24’52”E.
Habitat
Begonia viscosa is found in secondary broad-leaved evergreen dry forests on very steep rocky slopes and on the top of remnant mountains composed of highly eroded crystalline marble-like limestone. It thrives at elevations ranging from 400 to 450 meters above sea level. It typically grows as a lithophytic undershrub with erect shoots to 2 meters tall in crevices of open vertical cliffs. It is locally common in its habitat.
Characteristics
Begonia viscosa is a deciduous or semideciduous undershrub that reaches a height of 1 to 1.5 (2) meters. It has succulent, glabrous stems that are cylindric, with a diameter of (8)1–1.5 cm. The plant is normally unbranching and displays a silvery-grey to light brownish color. It has numerous distichously placed leaf and stipule traces at nodes, which are distant on (3)5–10(15) mm. During the dry winter, it becomes leafless and forms new leaves at the end of the dry season in March to April. The stipules are semipersistent, ovate, and exhibit a broad base. They are acute, concave, measuring (1)1.5–2.5(3.5) cm in length and 0.5–1.5(2) cm in width. They are light green, occasionally with a pink tint, and have a scarious, membranous margin. The leaves are petiolate and hairy throughout with short glandular viscid capitate hairs. The petioles are cylindric, fleshy, succulent, and stout, with colors ranging from light green to pink to purple. They measure (2)3–6(10) cm in length. The leaf blade is transversely ovate, broadly cuneate to unequally cordate at the base, acute to shortly attenuate at the apex, and strongly asymmetric. It features palmate venation with numerous branching veins, measuring (3)4–10(12) cm in length and (4)6–18(22) cm in width. The leaves are palmately crisped and serrulate along the margin. They are densely glandular hairy below, sparsely hairy or subglabrous above, and come in various colors, including light green, green, green-grey, reddish-gray, purple, and purple-brown. They often have palmate irregular white spots.
Flower Details
The inflorescence of Begonia viscosa is axillary, erect, dichotomous, and bracteate. It forms a glandular hairy cyme that can reach (10)12–25(30) cm in height. The inflorescence arises by 1 (rarely 2) from the apical part of the stem and develops before or simultaneously with the formation of leaves. The peduncle measures (5)6–14(18) cm in length, longer than the leaves, and is light green to yellowish-green. It bears dichotomously branching axes with clusters of 6-20 flowers. The bracts are insignificant and found at distinctly swollen nodes. They are triangular, brownish, and measure 1–3 mm in length and width. The flowers are pedicellate, monosexual, subactinomorphic, dichlamydeous, and range from white to very light pink. The pedicels are straight, densely glandular hairy, and measure (0.5)1–1.8(2) cm in length. The tepals are sparsely glandular hairy on the outside. Staminate flowers typically have 2 sepals and 2 petals opposite each other. The sepals are broadly ovate to almost orbicular, measuring (8)10–12(14) mm in length and width. The petals are elliptic to narrowly obovate, (7)8–10 mm long, and (4)5–7 mm wide. There are numerous stamens arranged in numerous whorls on short stalks in a dense capitulum. The stamens are brightly yellow, with free filaments measuring 1–1.5 mm long and obovoid anthers about 1.5 mm long. The connective extends at the apex in the form of a small broad obtuse dent. Pistillate flowers typically have 2 sepals and 3 petals. The sepals are broadly obovate to almost orbicular, measuring (10)12–14(16) mm in length and width. The petals are elliptic to narrowly obovate, as long as the sepals, and are 7–8 mm wide. The styles are 3(4) and brightly yellow, measuring (2)3–5(6) mm tall. They are connate at the base and branch toward the apex, with stigmas that are turgid and densely setose-papillose. The ovary is inferior, composed of 3 carpels, light greenish, often with a pink or purple tint, and densely glandular hairy. It is 3-angular, with wings along each edge, with the apical wing being much larger. The placentation is axial bifid in the middle part and at the base, becoming parietal bifid in the apical part of the ovary. The capsules are dry, light brown, loculicidal, nodding, 3-locular, ovoid, and indistinctly triangular in section. They measure 8–12 mm in length and 6–8 mm in width, with 3 unequal wings. The apical wing is ovate and can reach up to 1.5 cm in height, much larger than the two band-like lateral wings. The seeds are ovoid, numerous, very small, and have a light brown reticulate testa.
Etymology
The species name "viscosa" reflects the viscid character of stipules, leaves, inflorescences, and flowers due to glandular hairs that produce a glue-like secretion and spread throughout almost all parts of the plant.
Comparison to Similar Species
Begonia viscosa appears to have an isolated taxonomical position. No similar or related species of the genus have been found or reported in Indochina. While the ovary placentation in the lower part of the ovary looks similar to placentation observed in some species of Sect. Diploclinium, toward the ovary apex, the placentation is distinctly parietal, typical for members of Sect. Coelocentrum. A certain relation to any presently known species of both mentioned sections cannot be traced. The viscid glandular indumentum on leaves, inflorescences, and flowers is very characteristic. In this regard, Begonia viscosa, together with the recently described B. glutinosa Kiew (Kiew, 2007), represents a unique example among Indochinese begonias.
References
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