Begonia aequilateralis is a herbaceous, monoecious and rhizomatous species belonging to the family Begoniaceae. It is endemic to Selangor, where it only grows in riverine areas and is attached to rocks in lowland forests. This species is listed as Vulnerable in the Malaysia Plant Red List because there are only 3 populations in Selangor, i.e., Bukit Lagong Forest Reserve, Sungai Buloh area, and Kota Damansara Community Park at Petaling Jaya. It is threatened by habitat loss and degradation due to human activities and land development (Chan, 2008).
The locals call this begonia as asam batu or asam riang. This species is also known as Equal-sided Begonia because the leaves are almost symmetrical. The leaf shape and the colour of the veins are similar to those of Begonia tampinica, but the leaf size is smaller (9−15 cm wide, 16−29 cm long and 1.5−2 mm thick). The leaf is dull, plain green above, with minute hairs and deep red veins underneath (Kiew, 2005), and the leaf stalk is reddish. The margin of the leaves is minutely toothed, while the tip is attenuated c. 0.75 to 2 cm long.
Meanwhile, the flowers are pink and whitish and have some tiny hairs. Like all begonias, Begonia aequilateralis is monoecious, meaning that both male and female flowers are on the same plant. Typically, male flowers bloom before female flowers. Each male flower has four narrowly oval tepals (the outer whorl in a flower in which petals and sepals are indistinguishable) with acute tips. The outer two tepals are tinged pink, while the inner two are normally white. Meanwhile, a female flower consists of five oval tepals which are either pinkish or pure white with a tinge of pink at the acute tip, and the stalk is greenish to deep pink. The anthers of the male flowers are narrowly oblong, whereas the styles and stigmas of the female flowers are yellow and spiral (pers. obs.). The fruit is like a splash cup pendent on a slender, stiff stalk. Also, each fruit has three wings of unequal size. The seeds are barrel-shaped, measuring approximately 0.3 mm long (Kiew, 2005).
This vulnerable begonia can be conserved ex situ, whereby the Forest Research Institute Malaysia (FRIM) has successfully propagated this species via cuttings (Sam, 2006), and new leaves were produced after 4 weeks of sowing (Tan et al., 2023). Meanwhile, reintroduction programme or expansion of population size in nearby protected areas are recommended because the population is small in the wild.
