Redwood Sorrel (Oxalis oregana) is the signature groundcover plant of the Pacific Northwest's majestic coastal redwood forests — a lush, carpet-forming wildflower whose large, shamrock-shaped leaves form an emerald understory carpet beneath the world's tallest trees. This shade-loving species has evolved a remarkable sensitivity to light: its leaves fold down like tiny umbrellas within minutes of being struck by direct sunbeams, protecting their delicate tissues from damage, then reopen when shade returns — a living, responsive carpet that constantly adjusts to the dappled light filtering through the redwood canopy.
• The defining groundcover plant of coastal redwood forests — forms extensive carpets under the world's tallest trees
• Leaves fold downward within minutes of being struck by direct sunlight, then reopen when shade returns
• The largest-leaved of all North American Oxalis species — leaflets can reach 5 cm across
• The specific epithet "oregana" refers to the Oregon Territory where it was first collected
• Edible in small quantities with a tangy, lemon-like flavor from oxalic acid
• Also called "Oregon Oxalis" and "Redwood Shamrock"
• Found in a narrow coastal strip from southwestern British Columbia through western Washington and Oregon to northwestern California
• Most abundant in the coastal redwood forests of northern California and southern Oregon
• Also occurs in coastal Sitka spruce and western hemlock forests
• Strictly limited to the Pacific Coast fog belt where summer humidity is high
• Grows at elevations from sea level to 1,000 m
• First described by Nuttall in 1834
• The genus Oxalis contains approximately 500 to 700 species worldwide
Rhizome:
• Slender, creeping, extensively branched, scaly
• Forms a dense, interconnected underground network
Leaves:
• Compound, with 3 broadly heart-shaped leaflets
• Each leaflet 2 to 5 cm long, prominently notched at the tip
• Bright green, often with silvery or purplish markings
• Leaves fold downward in direct sunlight (photonasty)
• Long petioles, 5 to 20 cm tall, green to reddish, with fine hairs
Stem:
• No erect stem — leaves and flowers arise directly from the rhizome
Flower:
• 1 to 3 flowers on slender stalks above the leaves
• Each flower 1.5 to 3 cm across
• 5 white to pale pink petals with lilac-pink veins
• 5 green sepals, fringed with orange glands
• Blooms March through September
Fruit:
• Capsule, ovoid, 5 to 8 mm long
• Seeds explosively ejected
• Found almost exclusively under the canopy of coast redwood, Sitka spruce, and western hemlock forests
• Requires deep shade and high humidity — intolerant of full sun and dry conditions
• The photonastic leaf-folding response protects leaves from photoinhibition and UV damage in sunflecks
• Often forms continuous, monospecific carpets covering hundreds of square meters
• Pollinated by small bees and flies
• Associates with sword fern, redwood violet, and giant chain fern in the redwood understory
• Rhizome networks can be centuries old in old-growth redwood groves
• Provides important habitat and moisture for forest floor invertebrates and amphibians
• Sensitive to forest disturbance — logging and canopy removal eliminate populations
• Plant in deep to partial shade — will NOT tolerate full sun
• Requires moist, humus-rich, acidic soil with excellent drainage
• Ideal for native woodland gardens under conifers, especially in the Pacific Northwest
• Plant rhizome divisions or container-grown stock in spring
• Keep soil consistently moist — requires the summer fog drip typical of its native habitat
• Mulch with redwood duff, pine needles, or leaf mold
• Combines beautifully with ferns, wild ginger, and inside-out flower for an authentic redwood forest floor garden
• Hardy to USDA Zone 6 with protection
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Redwood Sorrel performs one of the fastest and most visible plant movements in the temperate forest. When a shaft of sunlight penetrates the redwood canopy and strikes a leaf, specialized cells at the base of each leaflet detect the change in light intensity and begin pumping water out of their cells within seconds. This causes the leaflets to droop downward in as little as 5 to 10 minutes, folding like tiny umbrellas to protect their photosynthetic tissues from damage. When the sunbeam moves and shade returns, the cells slowly refill and the leaves reopen. On a typical summer day in the redwood forest, the sorrel carpet appears to breathe and pulse as sunflecks sweep across the forest floor, with leaves constantly folding and unfolding in a silent, slow-motion dance of light and shadow.
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