Yellow Archangel (Lamiastrum galeobdolon)

plants, terrestrial, tier 5

History & Introduction

Yellow archangel (also known as yellow dead nettle or yellow henbit) is Lamiaceae (Mint) family plant native to Europe and has been introduced as a horticultural plant across the northeast and midwest United States as a semi-evergreen, low-growing, groundcover or hanging basket plant with interesting variegated foliage. It has been found growing as far north as Newfoundland, Canada; and as far south as Jackson, Alabama. According to NY Flora Atlas, it has been found escaping from cultivation within Suffolk County since 2012. It is currently listed as prohibited in the state of Washington due to its invasiveness.

Within LIISMA, it is currently a Tier 1d species – however it is likely under surveyed and under reported; at the time of writing there are nearly 40 research grade sightings of this plant on iNaturalist from Brooklyn to East Hampton.

Identification

Habit – Fast growing evergreen to semi-evergreen perennial forb/herb. Often seen trailing in the shade or growing upright in full sun conditions. Roots at the nodes of stolons, forming dense mats. Grows 1-2’

Leaves – Opposite, oval or egg shaped with a cordate (heart-shaped) base. 1-3.5” long and up to 2.5” wide. Edges are toothed, may be bluntly rounded to sharp-pointed. Hairy, especially or most noticeably near the edges. Tip is as well bluntly to sharply pointed. Upper leaf surface may be entirely green or green with silvery-white variegation. Leaf undersides are sometimes purple-ish. Petiole (leaf-stalk) is up to 1” long. Leaves are aromatic when crushed.

Stem – Greenish-purple, square shaped; erect. Hairy especially along angles on the lower stem. Numerous stolons.

Flowers – Irregular, tubes 3/8 inch long, growing in whorls of 4-10 in leaf axils along the upper half of the stem. ¾ to 1 inch long, light yellow. Top petal forms a larger hood densely covered in short hairs and fringed with longer hairs all around the edge. The lower lip has 3 spreading lobes all about the same size, the center lobe streaked with darker orange-yellow. Calyx surrounding the base of the flower is about as long as the floral tube, hairy, and has 5 sharply pointed triangular lobes. Blooms April-June

Fruits – The calyx persists and holds 4 nutlets, each containing a single seed.

Lookalikes – Bishops goutweed (Aegopodium podagraria), spotted deadnettle (Lamium maculatum).

Habitat

Can grow in a wide range of habitats, but seems to thrive in deeply shaded wet areas such as muddy streambanks and moist floodplains. May also be seen in dry full sun conditions, growing slightly more erect. Often found as localized to large monocultures near landscape dumping areas or natural areas adjacent to garden plantings; along edges of trails.

Damage

Due to its evergreen/semi-evergreen nature, yellow archangel can shade out and displace native herbaceous plants such as spring ephemerals; which are already heavily displaced and over browsed by deer.
Can spread from tiny root or stem fragments, as well as from numerous seeds.

Prevention

Preventing the introduction of invasive plants is considered the most economically efficient means of invasive species control. This plant may be available in retail stores or found online. Avoid buying and planting this plant, and opt for habitat-specific native groundcovers. If you already have this plant in your garden, keep it contained within its bed by trimming it back and clipping flowers prior to setting seed. Prevent its spread by properly disposing of all clippings in municipal waste as opposed to composts, with regular yard waste, or in natural areas.

If you see this plant in a natural area, please map it using iNaturalist or iMapInvasives.

Native Alternatives: foam flower (Tiarella cordifolia), lady fern (Athyrium felix-femina) and wild ginger (Asarum canadense). Check out our For Gardeners resource page for information on where to purchase Native Plants within LIISMA.

Control

Manual Control

Hand pulling has been found to have various levels of success, and may be labor intensive. Due to its evergreen habit, manual removal can take place late winter-early spring prior to seed set and before other herbaceous plants may be present. Shallow roots can be relatively easy to pull if ground is soft; taking care to remove as much of the plant as possible, leaving no plant fragments behind. Newer and smaller infestations may respond better to hand pulling, or digging as seeds may not be prevalent in the seed bank.

Cutting/mowing alone has not proven to be effective, as yellow archangel often grows more vigorously after being cut.

Sheet mulching may be effective in dense patches by laying down 3-4” thick pieces of cardboard, being sure to overlap the edges as much as possible to ensure plants are completely covered and not growing through gaps. Monitor edges of cardboard closely for new growth.

Disposal

Do not dispose of this plant in a backyard compost or dump in natural areas. Be sure to remove as much of the plant as possible, place in black contractor/garbage bags and tie it up. Leave in the sun for a few days to solarize (allowing the plant to begin breaking down). Dispose of in municipal waste.

Chemical Control

According to a report from King County, WA, the best results have been found through a combination of glyphosate and one of the following: triclopyr, imazapyr, or aminopyralid. Glyphosate on its own will usually be about 60% effective, but with repeat treatments can work.

Combinations with cutting or mowing followed by herbicide treatment may increase effectiveness. Cut or mow early spring (April) prior to growth of natives, followed by desired chemical treatment. Be sure to choose a formulation that is appropriate for the site, and as always, follow all instructions on the pesticide label, it is the law.