If you encounter unfamiliar plants in your garden, it’s crucial to exercise caution, as some can be highly toxic or invasive. For instance, Giant Hogweed (Heracleum mantegazzianum) poses significant health risks; its sap can cause severe skin burns and sensitivity to sunlight. Similarly, Japanese Knotweed (Fallopia japonica) is an invasive species known for damaging property foundations and decreasing property values. In the UK, cultivating certain non-native invasive plants, including Japanese Knotweed, is illegal and can result in substantial fines. 

To ensure safety, familiarize yourself with common harmful plants in your region. If you identify a dangerous or invasive species, it’s advisable to consult with local environmental authorities or professional removal services for proper handling and disposal. Always wear protective clothing when dealing with unknown plants, and keep children and pets away from potentially hazardous vegetation.