Begonia

Hillebrandia sandwicensis and Begonia spp.

1. Identification and origin

Begonias belong mostly to the genus Begonia L., one of the largest genera of flowering plants, with more than 2,000 species distributed mainly in tropical and subtropical regions. Alongside this, there is Hillebrandia sandwicensis (A. Gray) Oliv., the only species of the genus Hillebrandia, endemic to Hawaii and phylogenetically distinct, although belonging to the same family (Begoniaceae).
The Begonia spp. have a diverse origin, with centres of diversity in Central and South America, tropical Africa and Southeast Asia.

2. Economic importance

Begonias are widely used as ornamental plants, both indoors and outdoors, due to the great diversity of leaf shapes, colours and patterns, as well as their prolonged flowering. They include groups of high commercial value, such as tuberous, rhizomatous and fibrous begonias. They are important in the global ornamentals market, with intensive production in nurseries and greenhouses. H. sandwicensis, being rare and endemic, is of mainly scientific and conservation importance.

3. Botanical characterization

The Begonia spp. are herbaceous, subshrubby or, rarely, shrubby plants, with generally asymmetric leaves, frequently ornamental. They may have fibrous stems, rhizomes or tubers, depending on the group. The flowers are unisexual, with monoecious plants, and have coloured tepals. The fruits are winged capsules containing numerous seeds.
H. sandwicensis is distinguished by having unique morphological characteristics within the family, including flowers with more pronounced symmetry and anatomical differences in the ovary and the tepals.

4. Soil and climate requirements

Begonias prefer humid, shaded or filtered-light environments, with mild temperatures (18–24 °C). They are sensitive to cold and to excess direct light. They require well-drained substrates, rich in organic matter and with a slightly acidic pH. Irrigation should be regular, avoiding waterlogging that favours rots.
H. sandwicensis occurs naturally in humid, shady ravines of Hawaiian montane forests, requiring high atmospheric humidity and soils rich in organic matter.

5. Main pests

• Aphids (Aphididae): sap-sucking and transmission of viruses.
• Whitefly (Bemisia tabaci): chlorosis and honeydew production.
• Mites (Tetranychidae): chlorotic spots and reduced vigour.
• Thrips (Thrips spp.): damage to leaves and flowers.
• Snails and slugs: leaf perforations, especially in humid environments.

6. Main diseases

• Powdery mildew (Erysiphe spp.): white mycelium on the leaves.
• Rots caused by Pythium, Phytophthora and Rhizoctonia: death of seedlings and root rot.
• Botrytis (Botrytis cinerea): necrosis on leaves and flowers in humid environments.
• Bacteria (Xanthomonas spp.): leaf spots and marginal necrosis.
• Viruses (Begomovirus, CMV): mosaics and leaf deformations.

7. General crop management

Management includes the selection of cultivars adapted to the growing environment, the use of well-drained substrates, controlled irrigation and adequate ventilation to reduce fungal diseases. The removal of old leaves and sanitary cleaning are essential. In commercial production, propagation is frequently carried out by leaf or stem cuttings or division of rhizomes. Pest control should favour preventive methods and regular monitoring.

Bibliographic references

• EPPO Global Database – Begonia spp..
• CABI – Invasive Species Compendium – Begonia spp..
• FAO (2020). Horticultural Crops – Global Production Data. FAOSTAT.
• Hughes, M., & Moonlight, P. (2021). Begonia: Diversity, Evolution and Conservation. Kew Publishing.
• Wagner, W. L., Herbst, D. R., & Sohmer, S. H. (1999). Manual of the Flowering Plants of Hawai‘i. University of Hawai‘i Press.