Orchids (Family Orchidaceae) - Biodiversity (Singapore)

Orchids belong to the plant family Orchidaceae, which is a diverse and widespread family of flowering plants, with blooms that are often colourful and sometimes scented.

Orchidaceae is one of the two largest families of flowering plants, with about 28,000 species distributed in about 763 genera.

The largest genera within the orchid family are Bulbophyllum (2,000 species), Epidendrum (1,500 species), Dendrobium (1,400 species) and Pleurothallis (1,000 species).

Orchids are cosmopolitan, occurring in almost every habitat apart from glaciers, with the highest diversity of orchids occurring in the tropics.

Most orchids are perennial epiphytes, which grow anchored to trees in the tropics and subtropic, others are lithophytes growing on rocks or rocky soil. These can also be considered humus epiphytes as they sometimes grow in humus accumulations in rock crevices and not directly on rocks with no additional substrate.

Other orchids including most temperate orchids are terrestrial and are found growing directly in the soil in grasslands or forest, probably to escape frost damage and surviving through winter. While most of these terrestrial orchid species are autotrophs and can make food on their own through photosynthesis, many lack chlorophyll, and are unable to photosynthesise. Instead, they rely on their “host” soil fungi to obtain energy and nutrients, through the formation of orchid mycorrhizae. The fungi involved include those that form ectomycorrhizas with trees and other woody plants. These orchids are known as myco-heterotrophs, but were formerly incorrectly described as saprophytes, as it was believed they gained their nutrition by breaking down organic matter directly.

While only a few species are achlorophyllous holoparasites, all orchids are myco-heterotrophic during germination and seedling growth, meaning they have a fungal symbiotic dependence during germination and at the seedling phase. Even photosynthetic adult plants continue to rely on a certain amount of carbon from their mycorrhizal fungal association.