Corsiaceae Plant Family

About the Corsiaceae or Corybas Family

Corsiaceae is a family of small, non- mycoheterotrophic plants that are found across the Southern Hemisphere. These unusual plants have adapted to living off fungi in the soil, earning them the nickname “orchid mushrooms”. There are around 18 genera and over 100 species within this family, which can be further divided into three tribes: Corsiinae, Mesechiteae, and Rhizanthellinae. Despite their small size and often hidden lifestyles, Corsiaceae play an important role in forest ecosystems, contributing to nutrient cycling and providing habitat for associated organisms.

Taxonomy and Classification

Corsiaceae is a family of flowering plants in the order Ericales. They are divided into three tribes: Corsiinae, Mesechiteae, and Rhizanthellinae. The family contains around 18 genera and over 100 species, characterized by their small size, lack of chlorophyll, and parasitic lifestyles. Corsiaceae has been classified under the subfamily Monotropoideae of the family Ericaceae in the past due to their comparable morphology. However, recent molecular evidence supports their current classification under their own family. Corsiaceae shares some similarities with other mycoheterotrophic plants such as Orchidaceae and Ericaceae, which also rely on fungi for nutrient acquisition.

Morphology and Characteristics

Corsiaceae are small, non- plants that range from 5 to 30 centimeters in height. They have fleshy, underground rhizomes that function as storage organs and allow them to survive long periods of dormancy. The above- stems are typically short and unbranched, and the leaves are reduced to small scales or absent altogether. Corsiaceae produces flowers that are bisexual, zygomorphic, and solitary, with three sepals and three petals. The flowers can be found in shades of white, yellow, pink, or red, and have a waxy surface. Corsiaceae often has a unique floral morphology, including complex pollination mechanisms such as the production of floral scent, the presence of nectar chambers, and modified stamens. These adaptations ensure that only specific species of insects are able to visit the flowers during pollination.

Distribution and Habitat

Corsiaceae is distributed throughout the Southern Hemisphere, with concentrations in South America, Australia, New Zealand and Pacific Islands. They are found in a variety of habitats, including temperate forests, rainforests, and subalpine areas. Corsiaceae is known to form associations only with certain fungal taxa, which influence their distribution and habitat preferences. They often grow in shaded areas with high humidity where suitable mycorrhizal fungi are available. While some species are widespread within their range, others have very limited distributions, occurring only in specific locations or regions. The family is not typically cultivated, so its occurrence is dependent on natural habitats.

Economic and Ecological Importance

Corsiaceae is a unique family of plants, offering insights into the evolution and adaptation of mycoheterotrophic species. While they may not have significant economic importance, Corsiaceae plays an important ecological role in forest ecosystems as they are part of the nutrient cycling processes. They provide habitat for associated fungi and organisms and contribute to overall biodiversity. Like other mycoheterotrophic plant families, Corsiaceae can be sensitive to changes in environmental conditions such as deforestation or soil disturbance. Therefore, further research on their distribution and ecology is necessary to understand how they may respond to future changes in their environment.

Notable Species

As Corsiaceae is a relatively small family with around 18 genera and over 100 species described to date, there are many noteworthy species worth mentioning. Here are just a few:

  • Corallorhiza striata: also known as the Striped Coralroot, this species is found in North America and is unique among Corsiaceae in having photosynthetic green leaves. It is a mycorrhizal associate of several trees such as Douglas Fir and Ponderosa Pine.

  • Gastrodia sesamoides: a species found in southern Australia that is used in Chinese traditional medicine for treating headaches and other ailments. It relies on fungi from the Ceratobasidiaceae family for its nutrient acquisition.

  • Rhizanthella gardneri: also known as the Underground Orchid, this species occurs only in Western Australia and is entirely underground. It relies solely on a specific fungus for its nutrition and pollination, making it one of the most extreme examples of mycoheterotrophy in the plant kingdom.

  • Cyrtosia javanica: a species found in Southeast Asia, which has been used in traditional medicine to treat snakebites. It grows a single, large, white flower that emits a strong fragrance, attracting moth pollinators.

Each of these species is unique in its own way, showcasing the diverse adaptations and characteristics that make Corsiaceae such an interesting and important family of plants.