Continental South-east Asia

Location

The region we are interested in here, which we will call mainland Southeast Asia, lies mainly around the Tropic of Cancer. Begonias usually grow in the intertropical zones:

• But here their range extends well north of the Tropic into certain Chinese provinces: Fujian, Sichuan, Guizhou.
• It then stretches along the Tropic from west to east: north-east India (Arunachal Pradesh, Assam), northern Myanmar (formerly Burma), northern Laos and northern Vietnam, and further north in the following Chinese provinces: Yunnan, Guangxi, Guangdong, Taiwan.
• Some species are even found in areas very far from the Tropic, such as the Chinese provinces of Shandong and Shanxi, more than 1,500 km north of it.

Why group together regions that cover such a vast area? Simply because, although some species are endemic to small areas, many have a range that extends across the whole zone.
For example, Begonia palmata Don is found in China, in the following provinces: Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hunan and Yunnan, as well as in Laos, Burma, Bhutan, Vietnam and India. This species also grows in Thailand, Nepal and Bangladesh; but few begonias from our area are found in these three countries, which we will therefore leave for a later study of the begonias of India and then of maritime Southeast Asia. Another example is the well-known B. rex Putzeys, which grows in China (Guangxi, Yunnan and Guizhou) as well as in Vietnam and north-east India.

To see a map of this region, click here.

A complex geography

The relief of this region is complicated overall: it consists of a series of steps descending from west to east and from north to south, the result of the collision between the Eurasian and Indian plates.

In south-west China, the Yunnan and Guizhou plateaus (between 1,000 and 3,000 m) are cut by deep, steep-sided gorges. To the south, in eastern Yunnan, Guizhou, Guangxi, Guangdong and Hainan Island, lies a vast karst* where the limestone has been carved into a veritable stone forest below 500 m in altitude, where a few forests still survive.

The mountainous region of Yunnan continues into northern Vietnam, with peaks of over 3,000 m, and into northern Laos, where densely wooded ranges and plateaus are cut by narrow, deep valleys and gorges, while in the south sparser vegetation covers limestone terraces.

China’s relief also extends into Myanmar, another mountainous country (with peaks over 5,000 m) made up of two north–south ranges: one, the Arakan, forms a natural barrier with India, and the other is the southern extension of the Shan massif in China, at around 1,000 m.

Throughout this area, rivers mostly flow through deeply incised valleys. They are:

• The Chang Jiang (or Yangtze Kiang, the “Blue River”), which rises in Tibet and crosses Yunnan before turning east.
• The Xi Jiang, the main river of southern China, which rises in the Himalayas, flows east and empties into the Pacific Ocean in the south.
• The Mekong (Lancang Jiang), which descends from the high mountains of Yunnan and crosses Laos from north to south, also emptying into the Pacific south of Indochina.
• The Salween (Nu Jiang), which crosses Yunnan before flowing into Myanmar and emptying into the Andaman Sea.
• The Red River (Honghe Jiang or Yuan Jiang), which rises in Yunnan, crosses northern Vietnam and empties into the Gulf of Tonkin.
• The Irrawaddy in Myanmar, which flows south and empties into the Bay of Bengal

The Yangtze, the Salween and the Mekong run parallel through Yunnan in spectacular, botanically very rich gorges, whose biodiversity is seriously threatened by dam-building projects.

Climate

In summer, from May to October, the Pacific Ocean drives warm, humid air into the Asian continent, bringing heavy rainfall in the form of cyclonic storms: this is the monsoon*. Rainfall decreases rapidly with distance from the coast; during this period temperatures are uniformly warm across our whole area, falling towards the east and with altitude. The Chinese provinces mentioned above and Laos then have a hot, humid tropical climate (with 80% humidity almost all year round in Guangxi); northern Myanmar, which is drier, is hot in summer; northern Vietnam, where the monsoon is softened by the position of the Gulf of Tonkin, is subtropical, less hot and less humid than the other regions.

Winter, when cold, dry winds dry out the whole of China, is marked by large temperature differences depending on latitude and altitude. This cool, dry season lasts from November to February: southern China, Laos and northern Vietnam, under tropical influence, have barely noticeable winters, while in Myanmar the winter monsoon brings some rain.

Forests in retreat, as everywhere

Throughout the area, as everywhere, the forest has shrunk considerably.

What remains today: in China, forest covers 25% of Yunnan, 40% of Guangxi (secondary forest on limestone), 30% of Guizhou and 50% of the islands of Taiwan and Hainan. The karst south-west of China was once the domain of evergreen sclerophyllous* forest on mid-altitude limestone mountains. An active reforestation policy is reportedly now under way in China.

In Laos, the forest is badly degraded and only 52% remains.

In northern Vietnam, between 25% (north-west) and 30% (north-east) of the original forest remains.

Myanmar still has mixed deciduous forests* (40% of forest cover, around the dry central zone), temperate or montane forests (26%, in the north and mountainous areas) and humid evergreen forests* (16%); the forest there is seriously threatened, notably by overexploitation of teak and padauk (rosewood).

In north-east India, at the foot of the Himalayas, there are still tropical forests (below 1,000 m) and subtropical forests (up to 2,000 m), relatively protected by their isolation.

Where are the begonias?

A hot, humid climate (in summer), deep wooded gorges and rocks are the essential ingredients for begonias…
In total, more than 200 species are found here (others are surely waiting to be discovered), and the table below shows the areas where they are most numerous (the number of species is approximate): the main “hotspot” is Yunnan, Guangxi, Guizhou, Guangdong, Taiwan and Vietnam.

Which begonias?

Here is a (non-exhaustive) list of the species found in these regions: (species with highlighted names are in the photo gallery)

Where do they grow?

In these regions, begonias are found:

• Almost always in forest, near rivers, in hilly or mountainous areas, from sea level up to 3,400 m.
• Often on slopes
• Sometimes on the forest floor litter
• Very often on rocks
• Almost always in damp, shady places.

The following species grow on limestone, in the karst areas of eastern Yunnan, southern Guangxi, northern Vietnam and northern Laos (about 60 species):

• Often from section Coelocentrum: asteropyrifolia austroguangxiensis biflora  cirrosa  crystallina curvicarpa  daxinensis debaoensis fangii fimbribracteata  guangxiensis  huangii   hurunensis jingxiensis lanternaria linguinensis  linyanii  longistyla  luochengensis luzhaiensis masoniana morsei ningmingensis obliquifolia  ornithophylla  phutoensis picturata platycarpa  porteri  pseudodaxinensis  pseudoleprosa  retinervia semiparietalis setulosopeltata  umbraculifolia  zhengyiana
• And in other sections: balansana  cavaleriei  chingii filiformis grandis guishanensis  leprosa lithophila  peltatifolia  picturata pseudodryadis psilophylla  sinofloribunda  suboblata  wangii
• Many species grow on cliffs, sometimes at the entrance to caves : biflora chingii crystallina curvicarpa debaoensis detianensis filiformis guangxiensis jingxiensis lithophila luzhaiensis masoniana morsei obliquifolia picturata porteri retinervia setulosopeltata

Which begonias?

• Rhizomatous begonias: these are the most numerous, and most of them are creeping
• Few are upright:  baviensis  chuyunshanensis clavicaulis  coptidifolia coptidimontana
• Some lose their leaves in winter: austrotaiwanensis dentatobracteata  forrestii  lancangensis
• Tuberous begonias:

A number of the begonias in this area (about thirty species) are tuberous plants that grow on rocks (rarely on limestone), especially at altitude (between 200 and 3,500 m – these are the begonias that grow highest), mainly in the Chinese provinces of Guangxi and Yunnan (see table below).

Their growth is deciduous*: all the above-ground parts die back in the dry season or in winter. The tuber, clinging to rocks or wedged in crevices, allows these plants to survive a harsh cold or dry season while storing food for the following season.

• A few tuberous begonias are found on limestone ; for example grandis lithophila  peii chingii
• Among the rhizomatous begonias, some have a  globular, tuber-like rhizome (it is almost a tuber): cehengensis  crassirostris  xishuiensis  yunnanensis
• Others are stoloniferous* : balansana  prostrata  mashanica  discrepans  duclouxii  ravenii repenticaulis  zhangii

Sources:

-Botanical Bulletin Academia Sinica (descriptions / photos)

-Systematics of Begonias section Coelocentrum (Begoniaceae): thesis by the student Shin-Ming Ku

-Study of the Begoniaceae by Gu Cuizhi / Ku Tsue-chih / Ching-I Peng / Nicholas / J. Turland

-Photo galleries: Asian Flora / Hort Log / Chenkustan / Zeke Huang / HQ Nguyen / Nature Campus

To see the botanical begonias of this habitat in photos, visit the dedicated image gallery by clicking here and for unidentified species by clicking here.