Marsileaceae

Illustration Pilularia globulifera0

Marsilea Bild0717

Marsilea Hawaii

Pilularia globulifera - Thomé

Marsileaceae is a family of ferns in the order Salviniales, which is part of the class Polypodiopsida. This family is unique among ferns due to its aquatic or semi-aquatic lifestyle and the unusual appearance of its members, which do not resemble typical ferns. The family Marsileaceae includes four genera: Marsilea, Pilularia, Regnellidium, and Azolla. However, Azolla is sometimes placed in its own family, Azollaceae, due to distinct genetic and morphological characteristics.

Description

Members of the Marsileaceae family are characterized by their rhizomatous growth form, with the rhizomes often creeping along or just below the soil surface. They are adapted to a variety of aquatic and semi-aquatic environments, from temporary ponds to permanent bodies of water. The leaves of Marsileaceae can be highly variable, ranging from clover-like in Marsilea to needle-like in Pilularia. Despite their diverse leaf shapes, all members of this family produce sporocarps, which are unique, hard, reproductive structures that protect the spores until conditions are favorable for their release.

Taxonomy

The taxonomy of Marsileaceae has been subject to revision, especially with the advent of molecular phylogenetic studies. These studies have helped clarify the relationships within the family and with other ferns. The family is now securely placed within the order Salviniales, which is part of the leptosporangiate ferns, a group characterized by their spore-producing structures.

Genera

• Marsilea - Known commonly as water clovers, this genus includes species with leaves that resemble a four-leaf clover. They are found worldwide in various aquatic and semi-aquatic environments.
• Pilularia - The pillworts, distinguished by their grass-like appearance, inhabit similar environments to Marsilea but are less widespread.
• Regnellidium - This genus contains only one species, Regnellidium diphyllum, which is native to South America. It has two-lobed leaves and is found in wetlands.
• Azolla - Often considered part of its own family, Azolla species are small, floating ferns that form symbiotic relationships with nitrogen-fixing cyanobacteria. They play a significant role in the nitrogen cycle of aquatic ecosystems.

Ecology

Marsileaceae species are adapted to a wide range of aquatic environments. Their ability to survive in both temporary and permanent water bodies allows them to occupy ecological niches unavailable to most other ferns. The sporocarps produced by these plants enable them to survive periods of drought, releasing their spores when conditions become favorable again. Additionally, the symbiotic relationship between Azolla species and cyanobacteria is of ecological and agricultural importance, as it contributes to the enrichment of aquatic habitats with nitrogen, enhancing the growth of other plants.

Conservation

Some species within the Marsileaceae family are considered rare or endangered, often due to habitat destruction and water pollution. Conservation efforts are necessary to protect these unique aquatic ferns and their habitats to ensure their survival for future generations.