Gunneraceae

Overview of Gunneraceae Plant Family

Gunneraceae is a small family of flowering plants within the order Gunnerales. The family is composed of only two genera, Gunnera and Myrothamnus, and approximately 100 species. Gunnera is the most widely known genus within this family, comprising around 90 species, while Myrothamnus contains only a few species that are found in Africa.

Taxonomy and Classification

The Gunneraceae family belongs to the Gunnerales order, which also includes three other families: Myrothamnaceae, Haloragaceae, and Casuarinaceae. Gunneraceae is the largest family among them.

The classification of the Gunneraceae family has been sometimes ambiguous, and there have been different approaches to defining it taxonomically. Previously, it had been placed under the order Haloragales, but molecular evidence now places it under its own order, Gunnerales. Both Gunnera and Myrothamnus have undergone changes in their taxonomic classification over time, with some species having been moved from one genus to the other.

Unique Characteristics

The Gunneraceae family is distinct from other plant families due to its large and showy herbaceous plants, which produce unique, umbrella-like inflorescences. The leaves of Gunnera are among the largest in the plant world, reaching over 3 meters in diameter in some species. The family is also known for its presence of rhizomatous stems or stolons. Additionally, Myrothamnus is one of the few plants capable of surviving extreme desiccation, shedding all its leaves and bark when water is scarce and resurrecting soon after rainfalls.

The Gunneraceae family is widely grown as an ornamental plant due to its unusual appearance, which can make a striking addition to any garden. Some species of Gunnera have also been used in traditional medicine for their diuretic and anti-inflammatory properties.

Distribution of the Gunneraceae family

The Gunneraceae family is distributed primarily in the tropical regions of the world, although some species can also be found in temperate regions. The family has a global distribution, with a significant presence in South America, Africa, Australia, and Southeast Asia.

In South America, the family is found in the Andes region, including Colombia, Ecuador, Peru, and Chile. In Africa, the family is distributed in the eastern regions, including Ethiopia, Kenya, and Tanzania. In Australia, the family is present in the eastern regions, including Queensland and New South Wales, while in Southeast Asia, the family is found in Indonesia, Malaysia, and the Philippines.

Habitat of the Gunneraceae family

Plants from the Gunneraceae family can be found in a variety of natural habitats, including wetlands, streams, rivers, and forests. The family exhibits a preference for humid environments with high rainfall, although some species can tolerate drier conditions.

The family is commonly found in riparian habitats, such as the banks of streams and rivers, or in wetland areas, and some species can even grow partially submerged in water. The family can also be found in forested areas, including rainforests and montane forests, where they typically grow in the understory or along the edges of forest clearings.

Ecological preferences and adaptations of the Gunneraceae family

The Gunneraceae family exhibits several ecological preferences and adaptations that allow them to survive in their preferred habitats. For instance, some species have adapted to growing in low-light conditions, enabling them to grow in the understory of forests where there is limited light penetration.

The family's preference for moist environments means that they have adapted to growing in soils with high water content, allowing them to absorb water and nutrients from the surrounding environment, even if their roots are partially or fully submerged in water.

Some species of the family, such as the species in the genus Gunnera, have large leaves that can reach up to 2.5 meters in diameter. These leaves help the plants to absorb as much sunlight as possible, maximising their ability to photosynthesise and produce energy.

Morphology and Structure of Plants in the Gunneraceae Family

The Gunneraceae family includes herbaceous or woody plants that are known for their large and showy leaves and flowers. The family consists of seven genera with approximately 120 species distributed in tropical and subtropical regions of the world, especially in South America and Africa.

One of the key anatomical features that characterizes the Gunneraceae family is the presence of interpetiolar stipules, which are structures that grow at the base of the petioles and protect the developing buds. These stipules are usually large and persistent, and sometimes they fuse to form a sheath around the stem.

The leaves of Gunneraceae plants are typically broad and peltate, which means that the petiole attaches to the center of the blade instead of the margin. This arrangement allows for efficient capture of sunlight and water, as well as protection of the growing point from herbivores and environmental stressors. The leaves may be simple or compound, and the margins can be smooth, toothed, or lobed, depending on the species.

The Gunneraceae family is also known for its unique inflorescences, which are borne on stout stems that arise from the leaf axils. The inflorescences can be either racemes or spikes, and they are surrounded by large and colorful bracts that resemble petals. The flowers are usually bisexual, radially symmetric, and have a cup-shaped calyx and corolla. The androecium consists of numerous stamens with elongated filaments and large anthers, while the gynoecium has a single compound pistil with several ovules.

Leaf Shapes, Flower Structures, and Other Variations in the Family

The Gunneraceae family exhibits some variations in leaf shapes, flower structures, and other distinctive characteristics across its different genera and species. For example:

• The genus Gunnera has the largest leaves in the plant kingdom, with blades that can reach up to 3 meters in diameter in the case of Gunnera manicata. The leaves are typically deeply lobed and have prominent veins, which are used for water transport and support.
• The genus Parasenegalia (formerly known as Tafalla) has compound leaves that resemble those of ferns, with multiple leaflets attached to a rachis. The leaflets are typically narrow and lanceolate, and they give the plant a feathery appearance.
• The genus Onderdonkia has small and inconspicuous flowers that lack petals and are wind-pollinated. The flowers produce large quantities of pollen, which is dispersed by the wind and can cause respiratory allergies.
• The genus Gunnerella has leaf blades that are divided into many segments, giving them a lacy or fern-like appearance. The flowers are small and white, and the bracts are inconspicuous.

These variations in leaf shapes, flower structures, and other distinctive characteristics reflect the diverse adaptations of the Gunneraceae family to different habitats, pollinators, and environmental conditions. Despite their differences, however, all members of the Gunneraceae family share a common ancestry and evolutionary history, which is reflected in their molecular and morphological traits.

Reproductive Strategies in Gunneraceae family

The Gunneraceae family consist of shrubs and occasionally small trees. This family exhibits both sexual and vegetative reproduction. The primary mode of reproduction is sexual via flowers that possess both male and female reproductive structures. However, some species of the family can reproduce by vegetative means.

Mechanisms of Reproduction

In the Gunneraceae family, flowers have both male and female reproductive structures but usually appear separately on distinct plants, that is, are dioecious. Male flowers contain numerous stamens, each with four pollen sacs that have a specialized mechanism for releasing pollen; while female flowers have a single two-part ovary, each with a sticky stigma to receive pollen and several stamens with no pollen. Some species, like the Colombian genus, Tovomita, are monoecious, which means male and female flowers are on the same plant.

Pollination is accomplished by species of insects such as beetles, bees, and flies. Flowers in the family usually produce nectar, with some species also having specialized floral structures to trap insects and ensure pollination.

Flowering Patterns and Pollination Strategies

Most species in the Gunneraceae family flower during the warm, rainy season. Flowers in the family usually produce nectar, and some species also have specialized floral structures, such as a pitfall trap, to attract and trap insects like beetles and flies. Once trapped in the flower, the insects are dusted with pollen before being released, facilitating pollination. Some species of the family have evolved to be pollinated by hummingbirds. Their flowers, which are usually red, are long tubular, and contain abundant nectar, thus specifically adapted to the avian pollinator.

Seed Dispersal Methods and Adaptations

Seeds from the Gunneraceae family often have fleshy and sweet-tasting pulp, thought to be an adaptation for the dispersal by birds. Some species have spines or barbs to catch onto the fur or feathers of animals, allowing seeds to be transported over long distances. Seeds have a relatively hard outer coat, which usually protects the embryo from dehydration and environmental stresses. In response to suitable environmental conditions, seeds can germinate, and new plants will emerge.

Economic Importance

The Gunneraceae family is known for its plants' numerous economic values. In particular, the family contains several species with medicinal properties, including Gunnera perpensa and G. tinctoria, both native to Africa and used in traditional medicine to treat various ailments, including skin diseases, diabetes, and respiratory disorders. Additionally, the roots of some species are used in the production of a South American alcoholic beverage known as "mucilage chicha."

In terms of culinary use, the young leaves and rhizomes of Gunnera manicata, commonly known as "giant rhubarb," can be eaten raw or cooked and are often used in salads or as a vegetable. In addition, the leaves of Gunnera tinctoria are used as a food wrap in areas of South Africa and are an essential ingredient in some soups and stews due to their sour taste.

Furthermore, several species of the Gunneraceae family are of industrial importance. The large leaves of Gunnera manicata can be used as umbrellas or as a natural roofing material in some parts of the world. Additionally, the plant's leaves contain fibers that are used in papermaking, and the rhizomes are used in manufacturing dye.

Ecological Importance

The Gunneraceae family plays a crucial role in the ecosystems where they are present. Many species are used as cover by numerous animals, including insects, birds, and mammals. In addition, their enormous leaves provide a stable microclimate conducive to the growth of other plants by regulating soil moisture levels. The dying leaves of these plants also serve as nutrient sources for microorganisms and smaller animals, thus promoting soil fertility.

In addition, the Gunneraceae family's pollen and nectar serve as a food source for various pollinators, including bees, butterflies, and hummingbirds. Moreover, they help control soil erosion by slowing down runoff water and improving soil structure through the extensive root systems present in some species.

Conservation Status

Some species of the Gunneraceae family are under threat due to habitat destruction, overexploitation, and climate change. For example, Gunnera perpensa is considered a vulnerable species because of the loss of its natural habitat and illegal harvesting for medicinal purposes. Similarly, Gunnera tinctoria is classified as endangered, with its numbers reportedly declining due to habitat degradation and over-harvesting for medicinal and food purposes.

Various conservation efforts are underway to protect these plant species, including the establishment of protected areas, restoration of degraded habitats, and sustainable harvesting practices. For example, the Biodiversity Conservation Institute (BCI) has started several conservation projects focused on protecting the Gunneraceae family in South Africa, including the cultivation of species with medicinal properties, such as Gunnera perpensa, for economic reasons while ensuring their conservation.