# Japanese knotweed (*Reynoutria japonica*) Japanese knotweed is a tall plant with big green leaves and white flowers. It grows quickly and can be found in many places, often near water. It's important to know about it because it can take over other plants! - **Category:** [Plants](https://www.snappit.app/explore/categories/plant) - **Rarity:** Common - **Danger:** 2/5 · Low - **Snaps:** 47 - **Habitat:** Urban areas ![Japanese knotweed](https://commons.wikimedia.org/w/index.php?title=Special:Redirect/file/Reynoutria_japonica_in_Brastad_1.jpg&width=800) Photo: W.carter, CC0 · [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Reynoutria_japonica_in_Brastad_1.jpg) ## Appearance The Japanese knotweed has sturdy, hollow stems that are often reddish-purple, resembling bamboo. Its leaves are heart-shaped or spade-like, bright green, and grow alternately along the stem, making it distinct from many native plants. Small, creamy-white flowers appear in clusters. ## Taxonomy - **Kingdom:** Plantae - **Phylum:** Tracheophyta - **Class:** Magnoliopsida - **Order:** Caryophyllales - **Family:** Polygonaceae - **Genus:** Reynoutria ## Interesting facts - Its roots can break through concrete and asphalt! - Some call it the "Hulk Plant" because it's so tough to get rid of! - This plant can grow a whole foot taller in just one summer day! - Young knotweed shoots are eaten like rhubarb in Japan for tasty treats! ## Special abilities - **Root Power!:** Japanese knotweed can grow incredibly deep and strong roots that help it break through concrete and even house foundations! - **Super Regenerator!:** Japanese knotweed can regrow from tiny stem or root fragments, helping it quickly spread and survive almost any damage. - **Shade Conqueror!:** Japanese knotweed grows so fast and dense that it shades out other plants, helping it dominate new areas quickly. ## Measurements & details - **Height:** 200-400 cm - **Spread:** 100-500 cm - **Flower Size:** 0.1-0.3 cm - **Bloom Season:** Late_summer_early_fall - **Edible:** Yes - **Toxicity:** Mild - **Lifecycle:** Perennial - **Pollination Method:** Insect ## Ecological connections - **Pollinates:** European honey bee (*Apis mellifera*) — Visits its white summer flowers. - **Eats:** knotweed leaf beetle (*Gallerucida bifasciata*) — Beetle larvae munch its leaves (native). - **Shelter:** [house sparrow](https://www.snappit.app/explore/house-sparrow) (*Passer domesticus*) — Small birds hide in dense thickets. ## Traits - [Deciduous](https://www.snappit.app/explore/traits/deciduous): Deciduous plants periodically shed all their leaves, typically during autumn or dry seasons. - [Flowering](https://www.snappit.app/explore/traits/flowering): Flowering plants are any plants that produce flowers as part of their reproductive cycle. - [Medicinal](https://www.snappit.app/explore/traits/medicinal): Medicinal plants possess chemical compounds that can be used for therapeutic purposes to treat illnesses or maintain health. - [Pollinator Magnet](https://www.snappit.app/explore/traits/pollinator-magnet): Describes plants that are particularly attractive and beneficial to a wide range of pollinating organisms. - [Rapid Growing](https://www.snappit.app/explore/traits/rapid-growing): Rapid growing plants exhibit accelerated growth rates, quickly increasing in size and biomass within a short period. - [Urban Friendly](https://www.snappit.app/explore/traits/urban-friendly): This habitat trait indicates species that can coexist with humans in urban and suburban environments, utilizing man-made structures and green spaces. - [Invasive](https://www.snappit.app/explore/traits/invasive): Invasive species are non-native organisms that cause harm to the environment, economy, or human health. ## Collections - [Plants](https://www.snappit.app/explore/collections/plants) ## Safety **Danger:** 2/5 · Low Do not touch or eat any part of the plant without asking an adult first. ## Frequently Asked Questions ### How to identify Japanese knotweed? Start with the whole plant, then compare leaf arrangement, leaf edges, stems and any flowers or fruit. Opposite leaves grow in pairs; alternate leaves come one at a time along the stem. These details tell you far more together than a single green leaf does. Plant Identifier: upload a photo and compare the visible details. ### How tall is Japanese knotweed? 200-400 cm ### How wide does Japanese knotweed spread? 100-500 cm ### How big are the flowers on Japanese knotweed? 0.1-0.3 cm ### When does Japanese knotweed bloom? Late_summer_early_fall ### Is Japanese knotweed edible? Yes ### Is Japanese knotweed toxic? Mild ### What is Japanese knotweed's lifecycle? Perennial ## Where to spot - [American Baptist College](https://www.snappit.app/guides/places/american-baptist-college) — Tennessee, US · Campus - [Ames Nowell State Park](https://www.snappit.app/guides/places/ames-nowell-state-park) — Massachusetts, US · State Park - [Arden Park–East Boston Historic District](https://www.snappit.app/guides/places/arden-park-east-boston-historic-district) — Michigan, US · Historic District - [Blackhand Gorge State Nature Preserve](https://www.snappit.app/guides/places/blackhand-gorge-state-nature-preserve) — Ohio, US · Nature Reserve - [Brooklyn Botanic Garden](https://www.snappit.app/guides/places/brooklyn-botanic-garden) — New York, US · Botanical Garden - [Carriage Paths, Bridges and Gatehouses](https://www.snappit.app/guides/places/carriage-paths-bridges-and-gatehouses) — Maine, US · Historic District [View all places to see Japanese knotweed](https://www.snappit.app/guides/where-to-see/japanese-knotweed) ## More Plants - [white snakeroot](https://www.snappit.app/explore/white-snakeroot) (*Ageratina altissima*) - [tree-of-heaven](https://www.snappit.app/explore/tree-of-heaven) (*Ailanthus altissima*) - [western sword fern](https://www.snappit.app/explore/western-sword-fern) (*Polystichum munitum*) - [common milkweed](https://www.snappit.app/explore/common-milkweed) (*Asclepias syriaca*) --- Source: [Japanese knotweed: Facts & Places to See — Snappit](https://www.snappit.app/explore/japanese-knotweed)