The ecological impact of Thalia dealbata in China: A non-native species analysis
By Francine Hou: King’s College Hangzhou School
Instructor: Luqin Sun, Dipont School of Arts and Science
Abstract: Thalia dealbata (T. dealbata), commonly known as powdery alligator-flag, is an aquatic plant native to the southeastern United States, recognized for its environmental and ornamental significance. However, its introduction to China has sparked concerns due to its dominance, resilience, and unique pollination mechanisms, which may pose risks to local ecosystems. This paper examines the current status of T. dealbata in China, assessing its impact on biodiversity and ecosystem dynamics. Through a comprehensive review of existing literature and field observations, we assess the invasive potential of the species and classify it as a species of “high invasive risk” in China. Additionally, we propose further research into the ecological impacts of its unique pollination mechanism and have set up plausible methods of measuring the potential consequences that the mechanism may have on local food chains and biodiversity.
Key words: Thalia dealbata, invasive species, non-native species, aquatic plant, biodiversity, pollination mechanism
Francine Hou. The ecological impact of Thalia dealbata in China: A non-native species analysis. BioGreen - Biodiversity Conservation and Green Development. Vol. 1, January 2025. Total Issues 72. ISSN2749-9065
1. Introduction
Thalia dealbata (T. dealbata), commonly known as powdery alligator-flag or powdery thalia, is a species of aquatic plant native to the southeastern United States. As a valuable plant, the Thalia dealbata has both environmental and ornamental value (Chang et al., 2024). However, the dominance and resilience of the plant, paired with its unique pollination mechanism, has raised concerns about potential ecological harm from this non-native species in China. This paper aims to explore the status of T. dealbata in China and its implications for local biodiversity and ecosystem management.
2. Background
T. dealbata is a perennial herbaceous species within the Marantaceae family, commonly known as the powdery alligator-flag, hardy canna, or powdery thalia.
2.1 Morphological Characteristics
The emergent aquatic plant reaches a height of 100-250 cm, with foliage spanning 60-150 cm. The leaves are ovate-lanceolate to oblong, with dimensions of 20-50 cm in length and 10-20 cm in width, and exhibit a hard, papery texture. The leaf surface is gray green with purple edges, and the entire margin is smooth. The dorsal surface of the leaves is covered in a waterproof white powder. (North Carolina Extension Gardener Toolbox)
The flowers of this plant are arranged in sessile pairs and exhibit zygomorphy. Each flower has three purple-colored sepals, and three petals fused at their base. They are in bloom through the months of May to September with fruits throughout the summer (Powdery Thalia, United States Department Of Agriculture Natural Resources Conservation Service). Once the fruits turn brown, seeds can be collected from its thin shell.
2.2 Reproduction
As a plant in the Marantaceae family (Wilson & Morrison, 2000), the T. dealbata is capable of a specialized pollination method known as explosive secondary pollen presentation. This mechanism relies on the sensitivity of the flower stamen and style (Aruli & Reddi, 1995), where vigorous movement triggered by a pollinator would cause the style to be thrusted forward, depositing pollen onto the pollinator. Adapted to this mechanism, the pollen grains of the T. dealbata are smooth and large as this increases the surface area touching the stigma (Kennedy, 1978). This mechanism serves two purposes: pollen deposition, where the sudden action forces the pollinator into contact with the anthers, depositing pollen onto its body; and pollen collection, where the motion facilitates the retrieval of pollen from the pollinator, ensuring cross-pollination.
The mechanism is advantageous for the plants because it maximizes the efficiency of pollen transfer while minimizing the amount of wasted pollen. Additionally, it ensures that only the right pollinators - typically specific bee species - trigger the pollen transfer (Davis, 1987), ensuring high reproductive success in the competitive ecosystems in which they natively inhabit.
The effects of this pollination method on foreign environments will be explored later.
2.3 Native Habitat and Distribution
In its native range, T. dealbata is found in the southeastern United States, primarily in states such as Florida, Louisiana, and Texas. (Flora of North America)
The plant typically thrives along rivers and lakes where the soil contains high levels of organic matter and can tolerate nutrient levels similar to those found in wastewater from typical single-family home septic systems (Powdery T., United States Department Of Agriculture Natural Resources Conservation Service). This tolerance makes it extremely adaptable and able to thrive in areas not suitable for the growth of other more sensitive species, thus potentially creating a threat of invasion.
3. Introduction to China
Although it is unclear what the original means of introduction of the T. dealbata to China was, it is likely due to its ornamental or environmental value, especially in purification and pollution control (Chang et al., 2024). The plant tolerates acidic, alkaline, and water-logged soils and requires very little maintenance. Its adaptability to a range of climates and ability to thrive in and improve eutrophic waters have made it a valuable addition to artificial wetlands and urban landscaping projects in China (Li, 2021), especially with the growing trend of urban greening.
That said, China’s booming economy and rapid urbanization is resulting in an invasive species crisis (Ding etc., 2008), with a rapidly growing population of these resilient, highly reproductive plants in the southwestern and eastern regions in particular (Yan etc., 2014). With the increasing change in climate, the distribution of these alien aquatic plants is reaching higher altitudes and larger regions, sharpening the threat of invasive species (Wu & Ding, 2019). Although the plants may have originally been introduced for their beneficial ornamental or environmental value, the research on the long-term effects of certain non-native plants has not been made enough to determine the net benefit of its introduction. Thus, it is imperative that steps are to be taken to assess the invasive risk of aquatic non-native species like the T. dealbata.
4. Positive Ecological Impacts
The T. dealbata, like many other non-native aquatic plants, can bring both immense ornamental and restoration uses. They are a great addition to gardens and lakes with their large round leaves and vibrant purple flowers. Additionally, the functional uses of its planting are abundant and beneficial to environmental conservation and restoration efforts.
4.1 Purification
The T. dealbata has been referenced in several studies for its effectiveness in purifying polluted water. This includes the removal of excess Phosphorus through the synthesis of biochar microspheres derived from T. dealbata (Cui etc., 2016), and the remediation of cadmium-containing soil, which would otherwise produce toxic rice if planted directly (Genchi etc., 2020), by intercropping it between rice (Ni etc., 2024). The ability to restore polluted soil is especially rewarding for agricultural production and can enhance the efficiency of land use, providing economic benefits to the area as well.
Nitrogen pollution is another severe environmental hazard that requires improvement. For example, the excess nutrients degrade soil and create dead zones through eutrophication of surface waters. Luckily, T. dealbata has also been found to have the highest efficiency in total nitrogen removal compared to several others when planted in constructed wetlands (Wu etc., 2021), thus making it an effective and natural way of managing nitrogen pollution.
Studies have examined the allelopathic effects of T. dealbata and other macrophytes on cyanobacteria (Zhang, 2011), using the aqueous root extracts of the plant. Biochemical analyses of the samples showed that exposure to the extract reduced the ability of the cyanobacteria to proliferate, likely due to the lipid peroxidation of the cyanobacteria which damages the cell membrane and other key parts of the structure. The study was concluded with a confirmation of the use of macrophytes like T. dealbata to support ecological restoration.
T. dealbata has been demonstrated to offer the benefits of water purification, waste biomass utilization, and increased productive land use, allowing for more agricultural productivity for the area.
These research results have been applied in a Nanping sewage facility (Li, 2021) and the plant has been found in lining artificial reservoirs and wetlands.
5. Negative Ecological Impacts
5.1 Effects on Native Flora
Previous research on the competition that the T. dealbata brings to the local ecosystem has found that not only is the plant “highly aggressive” but also very reproductive and holds “high risk of invasion” (Li, 2021). T. dealbata has also been tested to be able to withstand two months of storage at zero degrees Celsius, making it a very tenacious and adaptable plant. Such resilience makes it a threat to local species as it will rapidly expand in population and create high competition for resources in the area (Gioria, 2023). Ultimately, this results in the loss of biodiversity and the domino-effect of a deteriorating local ecosystem.
There has also been incidence of T. dealbata plants in Hungary exhibiting a growing Sugarcane mosaic virus infection (Agoston, 2023), a plant pathogenic virus that causes the destruction of chlorophyll and thus hinders the growth abilities of sugarcane plants (Lu etc., 1984). Although it is the first and only case of such infection, the possibility of more undocumented cases is not negligible and could further pose threats to the local plant population. If such infected species were to be planted in alternation with rice as a method of reducing cadmium levels in the soil (previously mentioned above), it would pose severe risks to the entire crop.
5.2 Effects on Fauna
The plant’s unique explosive pollination mechanism that, while well-adapted for its native ecosystem, may have ecological consequences in its new environment that warrant closer examination. The T. dealbata flowers are structured in a manner that can inadvertently trap visiting pollinators, often leading to smaller insects being trapped and starved to death within the floral tube. This phenomenon poses a significant concern for native pollinator populations (Beth Chatto) and may be a detriment to local plant diversity. The scarcity of pollinators, an issue that has already plagued the globe due to pollution and rapid urbanization, would reduce the number of plants that can successfully reproduce sexually through natural pollination. This in turn reduces seed production, hinders plant regeneration and triggers a cascading effect throughout the food web (Johnson etc., 2002). This collapse of the food chain may also occur directly. If too many small insects - that are typically prey for other water-residing organisms - are unintentionally trapped and killed by T. dealbata, it results in a decline in population of these insects, leading to higher competition for food resources for secondary consumers. In worse case scenarios, this pattern will continue up the food chain, affecting all organisms in the local ecosystem. As a result, the balance of the local ecosystem is disrupted and a loss in biodiversity ensues. The lack of biodiversity is well-known in the scientific community for altering ecosystem productivity and destabilizing the stability of the ecosystem. If the T. dealbata has the potential to become a dominating plant in the area, the scenarios above are worthy of noting.
6. Invasive Potential
Although the T. dealbata has yet to be identified as an invasive species by major environmental agencies, regional studies in the British Isles and areas in China have identified it as having moderate ecological risk and invasive potential.
The plant also holds a score from the Australian Weed Risk Assessment (Gordon, 2010) index much higher than its cutoff of 6, making it a species of high invasive risk (Chen & Ding, 2011). Perhaps a lack of consensus is what prevents the plant from receiving a formal and universally recognized level of risk.
7. Conclusion
While further research is needed to fully understand its long-term impacts, initial observations suggest that this non-native species has the potential to alter local ecosystems through its resistance and adaptability to extreme temperatures and environments. Unfortunately, the author has yet to find research or information on the effects of the explosive style mechanism on the local insect population and pollination status, but the author hopes that other researchers could one day gain the opportunity and resources to complete a full study and reach a conclusion on said issue. This would include measuring the number of insects that can perish in a sprig of T. dealbata within a period of time and the species that are particularly vulnerable to the trap. With a more measurable account of the potential damage done by the plant’s pollination mechanism within non-native ecosystems, it would be much easier to assess the overall risk of the plant. Until further research can be made, the T. dealbata should be deemed a species of “high invasive risk” in China due to the compelling risk identification mechanism found in this previous 2011 risk assessment paper: (Chen & Ding, 2011). The author hopes that more studies can be made regarding T. dealbata and other non-native plants in China as its current prominence in local green infrastructure could potentially lead to an abundance of unintended consequences.
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