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Rachel Reeb

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City Nature Challenge: Noticing Invasive Plants 

by Rachel Reeb and Jessica Romano

This spring, thousands of people will join the City Nature Challenge, a global effort to document biodiversity safely and easily on the free iNaturalist app. Participating in the challenge is fun and rewarding – simply make observations of nature, take photos, and upload them to the app. The data collected during the challenge is shared with scientists around the world and helps them both document and better understand the diversity of species around us. This year’s challenge takes place April 25 through 28 for the observations, with a follow-up identification period from April 29 through May 1 when scientists and naturalists help observers properly identify the species they found. Participants will observe plants, insects, mammals, birds, mollusks, reptiles, amphibians, and more, right in their own neighborhoods. 

Alliaria petiolate, common name Garlic Mustard, is very commonly spotted during the City Nature Challenge and is easy to identify by its broad leaves and small white flowers. Credit: Katja Schulz from Washington, D. C., USA, CC BY 2.0, via Wikimedia Commons.

To help get us ready for this year’s challenge, Rachel Reeb, postdoctoral fellow in the Section of Botany at Carnegie Museum of Natural History, created this guide to finding and understanding invasive species of plants, including species like garlic mustard that is repeatedly one of the most often observed plants during the challenge. To get started, Rachel provided helpful definitions: 

Native or Indigenous species: Species that exist within an area due to natural evolution.

Introduced species: Species that have been introduced, by humans, to an area outside of its indigenous range. Roughly 25% of plant species in our environment are introduced.

Invasive species: A subset of introduced species which cause significant harm to the environment or human well-being. 

Naturalized species: A subset of introduced species which do not have demonstrated impacts on the environment or human well-being.

Lonicera maackii, known as the Amur Honeysuckle, originated in temperate areas of eastern Asia. Credit: Jay Sturner from USA, CC BY 2.0, via Wikimedia Commons.

Observing Invasive Plants

When is the best time to spot invasive plants? In the early stages of spring! Since introduced invasive plants evolved in a different part of the world, they often have unique life cycles that start and end at a different time than the rest of the plant community. Invasive species like garlic mustard, lesser celandine, periwinkle, multiflora rose, and Amur honeysuckle are some of the first to start their life cycles in the spring, providing a surprising pop of greenery to an otherwise dormant forest understory. This ‘head start’ in the growing season gives invasive plants an advantage because they gain priority access to soil nutrients and sunlight, while other plants are still dormant. 

Ficaria verna, or Lesser Celandine, blankets the ground in Frick Park. Credit: Rachel Reeb.

Unfortunately, what serves as an advantage for invasive plants is often a disadvantage to their neighbors, which now have a delayed start in the race to capture limited seasonal resources. Environmental experts in Pittsburgh are especially worried about the survival of rare native wildflowers, such as large white trillium, mayapple, and yellow trout lily. These plants, which have very specific habitat conditions and cannot easily relocate to new areas, are highly sensitive to changes in the environment and often cannot survive in areas where invasive plants are present.

During this year’s City Nature Challenge, we encourage you to take note of everything in nature, including the weeds. What do you notice about invasive plants in your area, like the timing of their life cycle, or how they interact with their neighbors? Have you ever wondered how these organisms came to be here? Many unwanted invasive plants were first introduced as popular garden center products. While some invasive species are now banned from sale, many can still be found in stores, like English ivy and Periwinkle vines.

Podophyllum peltatum, common name Mayapple, is a native species in Pennsylvania and sprouts early in spring, resembling little umbrellas on the landscape. Credit: Jessica Romano.

Here are helpful lists of species you may encounter in our area:

Invasive Species

  • Garlic Mustard 
  • Lesser Celandine
  • Knotweed 
  • Multiflora Rose
  • Amur Honeysuckle
  • Periwinkle / Vinca 
  • English Ivy 
  • Japanese Barberry 
  • Tree of heaven

Naturalized Species

  • Common Dandelion
  • White Clover

Native Spring Wildflowers 

  • Mayapple
  • Large White Trillium
  • Dutchman’s Breeches
  • Virginia Bluebells
  • Common Blue Violet
  • Yellow Trout Lily

How many of these species can you spot? Get your camera/phone/device and join the City Nature Challenge, April 25 through 28!

Rachel Reeb is a postdoctoral research fellow in the Section of Botany at Carnegie Museum of Natural History. Jessica Romano is Museum Education Writer at Carnegie Museum of Natural History.

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What’s in a Name? Japanese Knotweed or Itadori

by Rachel Reeb
hand holding a Japanese knotweed plant

We name what we notice, adopting or creating vocabulary to reflect all that our senses regularly engage.

Where multiple names exist in the same language for the same subject, nuance reigns. In Japan, for example, a historical collection of words referring to Reynoutria japonica (synonym: Fallopia japonica), the plant known commonly as itadori or Japanese knotweed, totaled to 689 terms. Some words referenced the plant’s shape and structure, others its sour taste, medicinal properties, seasonal appearance, or supporting habitat. Several dozen terms even noted audio characteristics, referencing the sound produced by the snapping of the plant’s stem.

Though the plant has deep cultural and ecological ties to its home range of Japan, Taiwan, China, and Korea, most of these connections are lost in its introduced range of western Pennsylvania, where it is considered to be an unwelcome invasive species. Information about how differently itadori is regarded in different parts of the world forces us to appreciate the diversity of human attitudes towards plants. Why are plant species perceived positively by some people, but negatively by others? To explore this question, a research paper documenting the rich cultural and ecological history of itadori in Japan (“Fallopia japonica (Japanese Knotweed) in Japan: Why Is It Not a Pest for Japanese People,” M. Shimoda and N. Yamasaki, 2016) made the journal club reading list for the scientists and educators involved in the collaborative Invasive Plant Species Education and Outreach Campaign funded by the Richard King Mellon Foundation.

Along the Allegheny River near Braeburn, Westmoreland County, spring growth of a knotweed stand that will block the view of the water by late June.

Itadori, or Japanese knotweed, has co-evolved with the humans, plants, and animals living in its home range for thousands of years. It’s no wonder that there are so many names for this plant in Japan, where people have co-existed with itadori and passed down their knowledge of the species over generations. Throughout history, humans found many uses for itadori in food, medicine, floral arrangements, and even as a children’s toy! 

Today, in Japan, itadori commonly grows around lawns and roadsides, but it is not considered to be a pest because it can easily be mowed and managed. In comparison, itadori was introduced to western Pennsylvania in the early 1900s, making our collective experience with the plant relatively recent by botanical standards. 

People widely planted itadori in ornamental gardens across the continent, but did not anticipate that it would escape cultivation and become established in nature. Here, many of the natural ‘checks and balances’ that stabilized itadori populations in the home range have been lost, including its insect pests, fungi, and plant competitors. Humans also lack deep ties to itadori in the introduced range, and consider it to be more detrimental than it is useful. The fast-growing plant often causes structural damage to buildings, is extremely expensive to manage, and displaces many of the native plants and animals we have formed connections with.

Thousands of years from now, itadori is likely to form new ecological and cultural connections in its introduced environment of Pennsylvania. What new names might we use to describe it, as our relationship to this plant evolves over time?

Rachel Reeb is a postdoctoral research fellow in the Section of Botany at Carnegie Museum of Natural History and content creator and project manager for the Invasive Species Awareness Campaign.

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Carnegie Museum of Natural History Blog Citation Information

Blog author: Reeb, Rachel
Publication date: November 30, 2023

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