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Klamath Weed

Klamath Weed

Hypericum perforatum

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How common: Common

Klamath Weed is a medium-sized, long-lived wildflower with bright yellow, star-like blooms. It often grows in sunny, dry, open places such as rocky slopes, field edges and roadsides. The leaves look as if they have tiny holes when held to the light. Warning: its sap can make skin extra sensitive to sunlight and may cause burns in strong sun.

Did you know?

  • The species name “perforatum” refers to the leaf’s see‑through dots that look like tiny holes.
  • Petal edges often show tiny black dots.

About the species

Identification

Upright plant 20–80 cm tall. Stems are firm with two narrow ridges. Leaves small (1–2.5 cm), smooth-edged and attached directly to the stem; they sit in facing pairs and show many tiny see‑through dots when held to the light. Flower clusters bear many bright yellow, five‑petalled flowers; the petal edges often have tiny black dots and there are many yellow threads in the centre. Afterwards it forms a dry capsule with many small seeds. Two‑ridged stems and the dotted leaves and petal edges help tell it from other yellow St John’s worts. Flowers in Finland from July to September.

Plant group

Herbaceous plants

Habitat

meadow

Toxicity

Its sap can burn the skin in sunlight – do not touch it with bare hands. Source: HUS Poison Information Centre (Finland), tel. 0800 147 111.

Flowering

Jul–Sep

About the habitat

Likes dry, sunny, open ground: rocky hillsides, grasslands and scrub, as well as field margins, roadsides, rail banks and other disturbed places. Common on Åland and along the south coast; rarer elsewhere in southern Finland; farther north an occasional newcomer.

Sources

Photo: Bff, CC BY-SA 4.0 https://commons.wikimedia.org/wiki/File:Hypericum perforatum20110702 023.jpg

Text: Pinkka: BIO-503 Suomen kasvisto ja kasvillisuus - Kulttuuriympäristöt: kedot, CC BY 4.0 https://laji.fi/taxon/MX.38302

Text: Pinkka: IPS-177 Fennoscandian flora - Hippophaë-Lythrum, CC BY 4.0 https://laji.fi/taxon/MX.38302

Text: Pinkka: Kasvitieteen retkeily Ahvenanmaalle - Kastelholman linna, CC BY 4.0 https://laji.fi/taxon/MX.38302

Text: Wikipedia (Finnish), CC BY-SA 4.0 https://fi.wikipedia.org/wiki/M%C3%A4kikuisma

See also