Hydrilla Plant

Hydrilla, also known as Water thyme or Indian star-vine, is commonly found in freshwater ecosystems such as lakes, rivers, and ponds. It is native to Asia but its rapid growth rate and high adaptations to various environmental changes make it the most invasive species worldwide. Over most of the United States and Florida, hydrilla has become the most problematic invasive aquatic weed and poses a threat to native vegetation. In this article, we will read about Hydrilla – characteristics, adaptations, and reproduction along with various adaptations of Hydrilla plant.

What is Hydrilla Plant?

Hydrilla is an obligate submerged, rooted perennial aquatic plant. It is herbaceous and has stems that spread horizontally, forming dense mats on the surface and outcompeting native plants. Its fast growth and ability to spread through fragments make it difficult to control in natural water habitats. Despite being invasive, hydrillas are used in aquariums and ponds for decoration.

Hydrilla Plant Classification

Hydrilla plant scientific name is Hydrilla verticillata. The scientific classification of Hydrilla plant is given below:

Kingdom	Plantae
Subkingdom	Tracheobionta
Superdivision	Spermatophyta
Division	Magnoliophyta (Angiospermophyta)
Class	Liliopsida
Subclass	Alismatidae
Order	Hydrocharitales
Family	Hydrocharitaceae
Genus	Hydrilla
Species	verticillata

Hydrilla Diagram

Given below is a labeled diagram of hydrilla:

Hydrilla Plant Characteristics

The characteristics of Hydrilla plant are given below:

• The Hydrilla has slender branching stems that can grow up to 1–2 m long depending on the water depth.
• The leaves are small, pointed, tightly arranged in whorls of 4 to 8 around the stem with small spines along the leaf margins.
• It is monoecious (have both male and female flowers on the same plant) or dioecious (have male and female flowers on different plants) forms with small, unisexual, solitary flowers featuring three sepals and three petals.
• Hydrilla reproduces primarily by vegetative means through fragmentation, turions (compact dormant buds), and tubers. Turions are dark green, conical form; spiny shoots produced in leaf axils, while tubers are whitish to yellow produced terminally on the rhizomes or stolons and may be submerged in sediment up to 30 cm deep.

Where is Hydrilla Found?

Hydrilla is an obligate submerged, rooted perennial aquatic plant. It is herbaceous and can tolerate a wide range of water conditions, including high and low nutrient concentrations, and extremely tolerant to salinities up to 7%. It prefers still or slow-moving waters and can colonize deeper depths due to its ability to grow in low light conditions. They can be found in many kinds of aquatic habitats, including rivers, lakes, ponds, reservoirs, and even tidal areas. These plants are deeply distributed throughout Asia, Europe, Africa, and Australia.

Reproduction in Hydrilla

Hydrilla can reproduce in both ways, sexually and asexually by vegetative means, contributing to its survival and spread.

Sexual Reproduction

Sexual reproduction in Hydrilla can lead to genetic variations that help the plant adapt to a broader range of environments. Hydrilla flowers are small, unnoticeable and often submerged. The pollination of H. verticillata is facilitated by epihydrophily.

• The pollen dispersal process of H. verticillata takes place only in sunlight. The male flowers lack a hypanthium, or “flower stalk,” instead reach the surface by detaching from the plant and floating up as a mature, air-filled bud.
• The male flowers are brought to the water surface by buoyancy from the attached gas bubble developed under the water.
• As the male flowers are exposed to sunlight, the sepals accumulate elastic force, causing the cracks in the top of the external bracts to expand and release the male flower.
• During this time interval, the male flowers do not release pollen until they reach the water surface.
• The female flower reaches the water surface by elongation of the hypanthium.
• The petals and sepals of the female flower form an inverted bell with an air bubble and the corolla opens and forms a funnel, which is hydrophobic, If the flower becomes submerged, the petals and sepals and close again enclosing an air bubble to protect the stigmas from water, ensuring air pollination
• Fertilisation occurs, and the female flowers develop into berry-like fruits containing seeds that can remain dormant in the sediment for long periods.

Vegetative Reproduction

Vegetative Reproduction occurs through stem fragmentation, axillary buds (turions), and tubers.

• Hydrilla is highly proficient in vegetative reproduction primarily through fragmentation, where fragmented pieces of stem that contain at least one node can sprout into a new plant, which can be dispersed by water movement, human activities, or the activities of animals.
• Tubers: Another method utilised by hydrilla is the formation of tubers, specialised underground storage structures that formed on the rhizomes and each one can produce 6,000 new tubers, allowing the plant to survive in adverse conditions and propagate rapidly. Tubers can remain dormant in the sediment and sprout under favourable conditions.
• Turion: Turions are formed in the leaf axils of the plant. They are broken off and once settled in the sediment they can sprout into a new plant. Axillary turions are on average half the size of tubers.

Unlike most plants, seed production in hydrilla is insignificant for reproduction. It appears that seed production is primarily used for long-distance dispersal. The monoecious form of hydrilla allocates more energy towards tuber and turion production compared to the dioecious form.

What is Hydrilla Experiment?

Hydrilla experiment was done by Jan Ingenhousz, a Dutch-born British physician and scientist, to prove that oxygen is produced during photosynthesis. Hydrilla is a small aquatic plant and easy to handle making it easy to set up the experiment. Hydrilla can breathe under water and stomata is absent so there is no gaseous exchange like land plants, thus it is easier to observe oxygen bubbles being released during photosynthesis. The presence of bubbles indicates oxygen production in photosynthesis.

What are the Adaptations of Hydrilla verticillata?

Hydrilla has developed special ways to survive and thrive in different water environments. This versatility makes it able to move into new areas and change the various aquatic ecosystems, outcompeting native vegetation. These characteristics make Hydrilla unique and distinguish it from other submersed aquatic plants.

• Hydrilla can tolerate different types of aquatic habitats and a wide range of water chemistry conditions, including calcareous ponds and streams, acidic and alkaline waters, as well as oligotrophic and eutrophic waters. Additionally, it can withstand high levels of salinity and raw sewage, making it a hardy species.
• In terms of nutrient uptake, Hydrilla has efficient mechanisms that allow it to rapidly deplete available resources and outcompete other aquatic plants. Its finely branched stems and compact leaf whorls maximise surface area for photosynthesis and nutrient absorption.
• Hydrilla does grow well in deep areas, it has adapted to grow in low light conditions, which may contribute to its rapid growth and ability to outcompete native vegetation.
• The thin, long, and hollow stems allow it to move freely along the water current. The stem of Hydrilla contains layers of epidermis, hypodermis, aerenchyma, and endodermis, particularly abundant in aerenchyma tissues (tissue containing air sacs) which provide buoyancy and help the plant float in the water. While it has less sclerenchyma and xylem tissues.
• The presence of hairy and fibrous roots allows water to penetrate the plant directly and capture air. Since the plant is buoyant and does not require roots for stability.
• The leaves are slender, elongated, and tapering to minimise resistance of water flow.
• Hydrilla’s turions, or dormant buds, can remain quiescent for extended periods of time in adverse condition, allowing the plant to quickly regrow and recolonize areas after treatment or environmental stress.
• Additionally, Hydrilla has rapid vegetative growth rates and a C4-like photosynthesis, which allows it to survive in a variety of aquatic environments.

Conclusion – Hydrilla Plant

In summary, the reproductive tactics and adaptive features of hydrilla enable it to establish itself as a Threatening Invasive species. Its ability to reproduce both sexually and vegetatively, along with its ability to live in various aquatic environments and get nutrients efficiently, allows it to outcompete native plants and ecosystems, effective management strategies must take into account these factors. By understanding the reproductive and adaptive mechanisms of hydrilla, we can effectively manage and conserve aquatic biodiversity.

FAQs on Hydrilla Plant – Reproduction and Adaptation

What is the Mode of Reproduction of Hydrilla?

Hydrilla reproduces both sexually and asexually. Asexual reproduction occurs through fragmentation, tubers, and axillary buds (turions). Sexual reproduction is insignificant and mainly serves for long-distance dispersal.

What are the Main Adaptations of Aquatic Plants?

Hydrilla has key adaptations that allow it to outcompete native plants. It can grow in low light conditions, absorbs nutrients and gases directly from water. tolerates various water conditions, and reproduces through four different methods.

What type of Pollination takes place in Hydrilla?

Hydrilla uses epihydrophily for pollination, where pollen is dispersed by water movement. Male flowers release pollen onto the water’s surface, which are then carried to female flowers by water currents.

Does Hydrilla have Stomata?

Hydrilla is a submerged aquatic plant, it is rooted and remains hidden under the water’s surface. Unlike other plants no transpiration happens underwater, so hydrilla leaves lack stomata, it absorbs water and gases through its general surface.

What is the Ecological Importance of Hydrilla?

Despite being an invasive plant species, hydrilla can offer habitat and food for certain aquatic organisms. It also serves various ecosystem functions, such as bioremediation, by purifying water contaminated with heavy metals.

Why is Hydrilla a Problem?

Hydrilla is a problem as it is an aggressive invasive species that forms dense mats that disrupts aquatic ecosystems and reduces biodiversity.

Why is Hydrilla Used?

Hydrilla is used in some regions for its ability to improve water quality by absorbing excess nutrients and providing habitat for aquatic life. Additionally, it can be utilized in aquaculture and as a food source for certain aquatic organisms.

What are the Special Features of Hydrilla?

Hydrilla exhibits special features such as rapid growth, ability to form dense mats, and efficient nutrient uptake, making it a highly invasive aquatic plant. Its adaptability to various environmental conditions contributes to its ability to outcompete native species and disrupt aquatic ecosystems.