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Broad-leaved Pepperweed

Lepidium latifolium

  • Name also: Broadleaved Peppergrass, Broadleaf Pepperweed, Broadleaved Pepperweed, Dittander, Dittany, Giant Whiteweed, Ironweed, Perennial Peppercress, Perennial Peppergrass, Perennial Pepperweed, Tall Whitetop, Virginia Pepperweed, Whitetop
  • Family: Mustard Family – Brassicaceae (Cruciferae)
  • Growing form: Perennial herb. Rootstock strong, branched. Forms stands.
  • Height: 30–100 cm (12–40 in.). Stem glabrous, bluish green.
  • Flower: Corolla regular (actinomorphic), white, approx. 0.5 cm (0.2 in.) wide; petals 4, approx. 2.5 mm (0.1 in.) long. Sepals 4. Stamens 6, of which 4 long and 2 short. Gynoecium fused, a single carpel. Inflorescence branched, densely flowered, raceme extends in fruiting stage.
  • Leaves: Alternate, lowest stalked, upper stalkless. Basal leaf blades elliptic–ovate, with densely serrated margins, stem leaf blades narrow, with entire margins.
  • Fruit: 2-seeded, round–elliptic, flat, with at most shallowly notched tip, virtually wingless, approx. 2.5 mm (0.1 in.) long silicula. Stalk delicate, about same length as silicula.
  • Habitat: Gravelly and stony beaches, seaweed banks.
  • Flowering time: July–August.
  • Endangerment: Near threatened, protected in all of Finland, including the Åland Islands.
    invasive alien species

Broad-leaved pepperweed is at its best during its flowering time at the end of July and beginning of August, when it is an arresting sight on the Finnish archipelago. The hundreds of small flowers on its many branches turn the whole plant white when they open, and this effect is further enhanced by the plant’s habit of forming large, pure stands: it uses its thick, many-branched rootstock to gradually spread across suitable habitats and pushes other possible competitors out of the way.

Broad-leaved pepperweed is probably native to the salt flats of Europe and Asia, and the plant is able to grow in the Baltic area very close to the coastline, where hardly any other plants can thrive. The movements of breakers or ice have no detrimental effect on the strong-rooted plant. Broad-leaved pepperweed only grows in Finland on the gravelly shores and seaweed banks of the Åland Islands and the Föglö and Dragsfjärd archipelagos. It can be found in casual or short-lived stands on the mainland too, close to harbours. The species probably arrived in Finland as seed or a piece of root with sea traffic from another Baltic port. Broad-leaved pepperweed is one of those species that is very rare in Finland but which grows abundantly on the southern side of the Baltic. It is also an old salad and culinary plant which is said to taste like mustard, onion and salt – although there is no information about the cultivation of the plant in Finland. Stands have been known about in Finland for hundreds of years, and they do not seem to be diminishing or increasing in size. It is actually quite surprising that thriving broad-leaved pepperweed has not expanded to nearby islands. Human activity is no threat to the plant on its small rocks.

Not protected everywhere

“…Broad-leaved pepperweed is a highly invasive herbaceous perennial. It can invade a wide range of habitats including riparian areas, wetlands, marshes, and floodplains. It adapts readily to natural and disturbed wetlands. As it establishes and expands, the plants create large monospecific stands that displace native plants and animals. It addition to impacting
alfalfa and pasture production, it has been reported to adversely affect food quality and nesting habitat for native birds and threaten the Carson’s Wandering Skipper butterfly…”

Text from
Weeds Gone Wild: Alien Plant Invaders of Natural Areas (USA) by
Plant Conservation Alliance’s Alien Plant Working Group

Compare purple loosestrife, Japanese knotweed and leafy spurge.

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