garden gardens horticulture invasive japanese knotweed pests problem problems species weed flowers Himalayan Balsam Impatiens glandulifera pest pink plants stand flower plant pod alien Fallopia japonica foreign invader Japanese Knotweed natural nature nuisance annual arctotheca calendula cape daisy cape dandelion cape gold cape marigold cape weed competitive daisylike edible groundcover hairy stems herb invasive-weed leaves lobed basal leaves noxious-weed ornamental petals prolific rosettes spreader squat perennial stolons taproot vigorous yellow arctotheca-calendula cape-daisy cape-dandelion cape-gold cape-marigold cape-weed capeweed hairy-stems lobed-basal-leaves squat-perennial abundance African wood-sorrel Bermuda-buttercup Bermuda-sorrel buttercup-oxalis Cape-cowslip Cape-sorrel cotyledon English-weed goat's-foot groud-cover oxalis oxalis-pes-caprae reflections sorrel sourgrass soursob soursop trifoliate-leaves tristylous-flowering-plant weeds wood-sorrel yellow-sorrel flora flowering abstract African-wood-sorrel background grass green greenery ground-cover water bright golden herbaceous-plant pointed-petals shade shadows stamens sunlight sunshine