Invasive: Yellow archangel (Lamiastrum galeobdolon)
Characteristics: Yellow archangel, or yellow Lamium, is a fast-growing, rhizomatous, trailing (sometimes upright) perennial ground cover. Stems are square in cross-section, and are typically less than 3 ft (1 m) tall. The hairy leaves are arranged in opposite pairs, and are variegated with white or silvery-grey markings, ovate, and coarsely toothed, roughly 2 inches (5 cm) long. Flowers are yellow and tubular, growing in pairs of clusters close to the stems, and borne from April to June. It may have a somewhat unpleasant odor, but not as pronounced as that of other mint-family plants.
Spread: Yellow archangel reproduces both vegetatively and by generous seed production, and can spread rapidly in gardens and natural areas. It tolerates a variety of soil and light conditions, making it a potential invader in many habitats, including otherwise healthy, mature forests. Root and stem fragments can both resprout, making dumping of this species a major route of introduction. Once established, yellow archangel readily overgrows low-growing native species, and may also climb over stumps and other obstacles. It has been known to overrun English ivy!
Control: Small infestations can be dug out by hand, though any root fragments that are left are likely to resprout. Sheet mulching may also be an option, though information on this is lacking. Appropriate herbicides can also be effective for infestations too large to remove manually. Any effort at eradication will likely involve multiple years and monitoring for regrowth in treated areas.
Native Replacements: Orange honeysuckle (Lonicera ciliosa, pictured below) is similar to yellow archangel both in preferred habitat and in growth habit (though it’s far less smothering than archangel), and gets showy, tubular orange flowers much beloved of hummingbirds. Woodland strawberry (Fragaria vesca) is an elegant, shade-tolerant perennial ground cover that also does well in habitat used by yellow archangel.