Currently, more than 650 species and cultivars of rhizomatous begonias are grown primarily for their foliage, which varies widely in shape, texture and colour. The leaves may be peltate (Begonia clypeifolia, Begonia nelumbiifolia), lobed or compound (Begonia carolineifolia, Begonia thiemi).
As the name suggests, begonias in this group have a rhizome, which consists of a thick stem with very short internodes. Depending on the species, it may be underground, creeping or upright.
The thickness of the rhizomes can range from 0.18 to 8 cm and more. Most rhizomatous begonias bloom from mid-winter to late spring. The degree of flowering, which varies enormously from one species to the next, is sensitive to growing conditions.
Most of the rhizomatous species at the Montréal Botanical Garden come from the Americas, but we also have some from the West Indies, Asia, Africa and Oceania. The first species with peltate leaves, Begonia nelumbiifolia, together with Begonia heracleifolia, was discovered in 1830 in Mexico by Ferdinand Deppe and C. J. Schide. The leaves can reach 30 cm in diameter at maturity. Other plants in this group include Begonia carolineifolia, which features a mass of upright rhizomes with compound-palmate leaves. This species, native to Mexico and Guatemala, was introduced to the Saint Petersburg Botanical Garden in 1822.
But not all rhizomatous begonias grown today were discovered in the 19th century.
Interest in rhizomatous begonias was kindled by the discovery of Begonia bowerae by Thomas MacDougall in 1948. With its small green leaves and black-edged veins, B. bowerae was used to create over 130 cultivars. Thomas MacDougall was an American botanist and explorer who died in 1973 during an expedition to Mexico, a country he visited periodically to collect plants. He discovered several new species of begonias, including B. cavum, B. kenworthyae and B. mazae.
During the 1940s, he brought back a species from Mexico, B. thiemi, which Casimir de Candolle described, in the 19th century, as a plant coming from Honduras, but which had remained unknown since then. This begonia has large green compound-palmate leaves, whose petiole can grow to more than one metre long and five centimetres wide. The inflorescence height can reach more than two metres.
One of the most beautiful rhizomatous begonia hybrids was created in 1967 at the Jardin botanique de Montréal. Begonia 'Eaglesham' is the result of cross between B. decora and B. masoniana, two Asian species. B. decora, which we grow in a terrarium, has small wine-red leaves. B. masoniana has large sturdy green leaves marked with brown crosses. Begonia ‘Eaglesham’ kept the colours of the first and the sturdiness of the second.
We also have some very interesting African rhizomatous begonias, even though they are not as widely cultivated, such as B. quadrialata and B. clypeifolia. B. quadrialata, which must be grown in a terrarium, has tiny leaves with a velvety upper surface. In its natural habitat, it grows in moist areas on rock faces. While seldom cultivated, B. clypeifolia has been known for a long time, since it was described in 1811 by J.D. Hooker. Native to the African tropical forest, this species has a creeping rhizome with glossy green peltate leaves. The flowers are light yellow. Another very fascinating species comes from Asia: B. roxburghii. This begonia, native to the Himalayas and Burma, produces male and female flowers on different plants. Here at the Garden, we have only female plants, which have upright stems with glossy green leaves.
Description and classification
Tuberous begonias are divided into five main types:
Semi-tuberous begonias have a bulb-like swollen area of the basal stem called a caudex. At ground level, the caudex looks like it went through an uncontrolled growth period before forming branches. A good example of a semi-tuberous begonia is the South African species Begonia dregei.
Bulbous begonias form bulbs or similar organs. But the only species that grows a bulb is Begonia socotrana, a plant native to Socotra Island that played a pivotal role in the development of Cheimantha and Hiemalis begonias.
Cheimantha begonias are hybrids of Begonia socotrana and Begonia dregei, which were first crossed in 1892 to produce ‘Gloire de Lorraine’. These begonias bloom in winter and produce single flowers in shades ranging from white to pink. Some Cheimantha cultivars are difficult to grow and require special care.
Hiemalis begonias were created by crossing different species of tuberous begonias with Begonia socotrana. The first hybrid in this group was created in 1833 by John Heal: Begonia Hiemalis 'Mrs. John Heal'. It is a cross between B. socotrana and Begonia ‘Visconte Deneraile’. These begonias bloom in winter and their flowers range from white to pink, from red and apricot to crimson and scarlet. The flowers are single, semi-double or double, depending on the variety. They are bushy, compact and sturdy plants. Some cultivars have upright stems while other tend to be creeping. At the Montréal Botanical Garden, we keep a few Hiemalis begonia cultivars, primarily from the Aphrodite series, which have double pink, red or peach flowers. We still have some specimens from the ‘Nelly Visser’ cultivar, created in 1948.
Tuberhybrida begonias, as the name suggests, are of hybrid origin and represent one of the greatest success stories in this area of horticulture. This group is the result of repeated crosses and backcrosses between Andean species. It includes erect and trailing types, with an immense variety of foliage and flowers. The flower measures 4 to 20 cm across and can be single, semi-double or double. The petals are flat or ruffled, and are white, cream, yellow, orange, pink, apricot pink, salmon pink, bright red, deep red or dark purple. There are no blue flowers. Begonias in this group have perennial semi-succulent flattened tubers and stems between 10 and 30 cm long, usually covered with hairs. The leaves have dentate, fringed and ciliate (hairy) margins.
The colourful, variegated foliage is what makes this group of begonias so popular. It was first developed in 1856 when Begonia rex was crossed with the following Asian species with ornamental foliage: B. annulata, B. decora, B. diadema, B. robusta, B. tenuifolia and B. xanthina.
Because of the frequent crosses, the leaves of Rex-cultorum begonias range widely in size, shape and colour.
Typical traits are short stems and heart-shaped, sometimes lobed, leaves that come in a variety or a combination of colours, with either silver or green backgrounds and highlights of pink, maroon, chocolate brown and nearly black.
The Rex-cultorum begonia collection at the Montréal Botanical Garden consists of nearly 90 cultivars, many of which were obtained in 1980 during the Floralies internationales horticultural exhibition held in Montreal. We also still have some cultivars that predate the 1950s: ‘Fairy’ with salmon pink leaves; ‘Lucy Clossom’ with upright stems; and ‘Peace’ with pale pink leaves.
Semperflorens-cultorum (or wax) begonias
This group of begonias consists of two categories: natural species and cultivars.
The species are themselves subdivided into two types: semperflorens and schmidtiana.
The first type, semperflorens, includes Begonia cucullata var. cucullata (B. semperflorens) and other varieties, as well as species that have similar growth habits and requirements. These plants can reach one metre in height.
The second type, schmidtiana, includes Begonia schmidtiana and species that are horticulturally similar; they are low growing and compact.
Semperflorens cultivars, known as Begonia Semperflorens-cultorum, are popular garden plants that are bushy and compact with slightly succulent stems. The ovate leaves are smooth and glossy and come in shades of green although some varieties have bronze- to black-red leaves. The plants produce abundant, long-lasting white, pink or red flowers. Most Semperflorens-cultorum begonias are easy to grow.
The collection at the Montréal Botanical Garden consists of about a dozen cultivars in this group, including ‘Indian Maid’, an early cultivar we received in 1940 that has orange-red flowers; ‘Cinderella’ with cherry red semi-double flowers; ‘Cindy Locks’ with yellow flowers; and ‘Thimbleberry’ with pink or red flowers.
Other types of begonias In addition to the previously described types, begonias can also be shrub-like, cane-stemmed, thick-stemmed, trailing or climbing.
Shrub-like begonias are grown primarily for their foliage, which comes in an extraordinary variety of shapes and colours. Begonia acutifolia, discovered in Jamaica in 1688 by Hans Sloane, was probably the first known begonia in this group. The leaves are acuminate, dentate and pubescent. One of the best-known begonias in this group has to be Begonia listada; originally from Brazil, it is grown for its dark green leaves with an emerald stripe down the centre. Two South American species, B. verossa, with its velvety leaves, and B. mollicaulis, with its abundant flowers, belong to this group too, as does B. serratipetala, with its deeply toothed red leaves.
The small group of thick-stemmed begonias is grown mostly by collectors and cross-breeders. Begonia dichotoma, discovered in tropical rainforests near Caracas, was introduced to England by Thomas Hoy in 1800. When it blooms, it produces a terminal inflorescence with many tiny white flowers. In 1826, Johnston sent seeds of B. dipetala, a species native to Bombay, India, to the Royal Botanic Garden, in Edinburgh. This species is highly prized by collectors for the large pink flowers that grow from the leaf axil. Begonia olbia, of horticultural origin, is also extremely interesting. The leaves are lobed, dentate and reddish. The upper leaf surface is olive green and slightly pubescent. The flowers are greenish. Another example from this group is B. ulmifolia, originally from the West Indies and South America, which, as its Latin nomenclature indicates, has leaves shaped much like the leaves on the elm it is named for.
Cane-stemmed begonias are generally grown for their long, pendant inflorescences. One of the most typical representatives of this group is Begonia coccinea. This species, native to Brazil, was introduced to England in 1841 by William Lobb, the first plant collector to work for Veitch & Sons Nurseries. The stems, which can reach a height of one metre, bear drooping clusters of coral-red flowers.
This group also contains the heritage cultivars ‘Président Carnot’ and ‘Lucerna’. The first, named in honour of the then president of the French Republic, was created in 1890 by Crozy, in Lyons. Wettstein, a gardener from Lucerne, Switzerland, created B. ‘Lucerna’ in 1892. These two begonias have tall upright stems and red flowers.
The small group of trailing or climbing begonias includes some highly interesting species. These begonias come mainly from South America and Africa. At the Montréal Botanical Garden, the majority of trailing or climbing begonias are grown in hanging baskets.
The first species in this group, Begonia glabra, was discovered in 1775 by Fusée Aublet, in French Guyana. This plant has profuse white flowers in spring. We also have some African species, such as B. convolvulacea, B. mannii and B. polygonoides. Also belonging to this group is B. mazae, native to Mexico, with small velvety leaves covered with brown stripes or spots.
Edible and medicinal begonias
Begonias are more than just ornamental plants. People in Africa, Asia and South America eat the leaves of some species, while in the Mossendjo district of the Congo, the leaves are used as a vegetable. Here are the directions for cooking Begonia ampla: first roll and cut the leaves into thin strips and boil them for twenty minutes, then rinse them in cold water. They can then be mixed with meat or other vegetables. It is dangerous to eat the leaves without first boiling them because they contain calcium oxalate crystals. Chimpanzees and gorillas in Gabon particularly enjoy Begonia mannii, one of their favourite foods. In the southern Chinese province of Yunnan, Begonia fimbristipula leaves are used to make herbal tea; the harvesting and drying of the leaves is a major local industry.
Begonias also have some medicinal properties. In New Guinea, Symbegonia moorena herbal tea is used to treat stomach ailments. Symbegonia fulvovillosa is used for mouth ulcers in children and colds; the stems are crushed to release the juice, which is ingested. In South America, begonia syrup or herbal tea is used to treat colds and fever (B. humilis, B. rotundifolia). The late Julia F. Morton, a professor at Miami University, noted that two unidentified species of begonias in Guatemala are used as compresses to heal various cuts and sores. A leaf decoction can also be prepared for stomach ulcers.
This section devoted to begonias would not be complete without a discussion of Hillebrandia sandwicensis.
This species, described in 1866 by Oliver, is found on only a few of the Hawaiian Islands, formerly called the Sandwich Islands, hence its species name sandwicensis.
The genus was named Hillebrandia after William Hillebrand (1821-1886), a physician who lived in Hawaii for twenty years. He wrote a Flora of the Hawaiian Islands, published in 1888.
Hillebrandia has tuberous rhizomes with upright, somewhat downy stems. The palmate leaves are lobed and bear fine bristles.
Based on articles by Denis Barabé in Quatre-Temps magazine.