Orchid

Orchids belong to the Orchidaceae family, one of the two largest families of flowering plants on Earth. This group is incredibly diverse and widespread, containing about 28,000 accepted species across roughly 700 genera. They are cosmopolitan plants, meaning they live on every continent except Antarctica. While they inhabit many environments, the richest diversity of orchid species is found in the tropics.

Orchids are often distinguished by specific physical traits, known as synapomorphies. Most orchid flowers exhibit bilateral symmetry, or zygomorphism, which means they can only be divided into two equal halves. A key feature is the labellum, a highly modified middle petal that often looks like a lip. In many species, the flower undergoes resupination, a process where it twists 180 degrees as it develops. This movement places the labellum at the bottom to serve as a landing stage for pollinators. The reproductive parts are also unique, as the stamens and carpels are fused into a single structure called a column.

Growth patterns in orchids vary depending on their environment. All orchids are perennial herbs, meaning they live for many years and lack woody structures. Some follow a monopodial growth pattern, where the stem grows from a single bud and adds leaves at the apex, such as the Vanda genus. Others are sympodial, meaning growth occurs at a front while older parts remain behind. Sympodial orchids may develop swollen pseudobulbs for storage.

Orchids also occupy different ecological niches. Terrestrial orchids grow in the ground and may use rhizomes or tubers. Many others are epiphytes, which are plants that grow upon a support, like a tree, rather than in soil. Epiphytic orchids often have aerial roots covered in velamen, a layer of dead cells. Some epiphytes, like Phalaenopsis, have leaves but use green roots to help with photosynthesis and prevent hypoxia, a lack of oxygen. Other specialized species, such as Taeniophyllum aphyllum, are entirely leafless and rely on their green roots for food.

Pollination in orchids is a highly specialized process. Most orchids deliver pollen in a single mass called a pollinium. When a pollinator enters a flower, it touches a sticky disc called a viscidium. As the insect leaves, it pulls the pollinium away via a structure called the caudicle or stipe. The pollinium then bends to a new position so that it will strike the stigma of the next flower the insect visits. Some orchids use extreme methods, such as the genus Ophrys, which uses mimicry to attract male insects by imitating the color, shape, and scent of a female insect.

History and discovery have shaped our understanding of these plants. In 1845, John Lindley introduced the term "orchid" as a shortened form of Orchidaceae. Later, in 1862, Charles Darwin published his book, Fertilisation of Orchids, after investigating their complex pollination mechanisms. We also have ancient evidence of their existence. A bee trapped in Miocene amber from 15–20 million years ago was found carrying pollen from the orchid Meliorchis caribea. Other fossils, like Succinanthera baltica from the Eocene, date back 40–55 million years.

Reproduction concludes with the development of a capsule. This fruit contains extremely small seeds, which can number over one million in a single capsule. Because these seeds lack endosperm, they depend on a symbiotic relationship with fungi to germinate. This process, known as being mycoheterotrophic, allows the fungi to provide necessary nutrients to the developing plant. This deep connection between orchids and fungal partners is essential for the survival of most species.