Osoberry
Oemleria cerasiformis
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Pacific Oenanthe
Oenanthe sarmentosa
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California Primrose
Oenothera avita
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California Evening-primrose
Oenothera avita ssp. avita
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California Evening Primrose
Oenothera avita ssp. californica
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Eureka Dunes Evening-primrose
Oenothera avita ssp. eurekensis
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Cave Evening-primrose
Oenothera cavernae
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Fragrant Evening Primrose
Oenothera cespitosa
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Cespitose Evening-primrose
Oenothera cespitosa ssp. crinita
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Dune Primrose
Oenothera deltoides
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Birdcage Evening Primrose
Oenothera deltoides ssp. cognata
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Birdcage Evening Primrose
Oenothera deltoides ssp. deltoides
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Antioch Dunes Evening Primrose
Oenothera deltoides ssp. howellii
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Piper's Evening Primrose
Oenothera deltoides ssp. piperi
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Hooker's Evening Primrose
Oenothera elata
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Hairy Evening Primrose
Oenothera elata ssp. hirsutissima
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Hooker's Evening Primrose
Oenothera elata ssp. hookeri
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Yellow Evening Primrose
Oenothera flava
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Long-stem Evening-primrose
Oenothera longissima
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Desert Evening Primrose
Oenothera primiveris
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Desert Evening Primrose
Oenothera primiveris ssp. primiveris
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Wild Honeysuckle
Oenothera suffrutescens
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Hairy Evening Primrose
Oenothera villosa
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Hairy Evening Primrose
Oenothera villosa ssp. strigosa
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Wolf's Evening-primrose
Oenothera wolfii
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Woodyfruit Evening Primrose
Oenothera xylocarpa
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Desert Ironwood
Olneya tesota
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Beavertail Pricklypear
Opuntia basilaris
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Beavertail Pricklypear
Opuntia basilaris var. basilaris
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Pancake Prickly-pear
Opuntia chlorotica
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Tulip Pricklypear
Opuntia engelmannii
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Engelmann Prickly-pear
Opuntia engelmannii var. engelmannii
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Coast Prickly Pear
Opuntia littoralis
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Chaparral Pricklypear
Opuntia oricola
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Tulip Pricklypear
Opuntia phaeacantha
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Plains Pricklypear
Opuntia polyacantha
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Grizzlybear Pricklypear
Opuntia polyacantha var. erinacea
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Porcupine Prickly-pear
Opuntia polyacantha var. hystricina
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Vasey's Prickly Pear
Opuntia vaseyi
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Tall Alpine-aster
Oreostemma elatum
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Broad Scaled Owl's Clover
Orthocarpus cuspidatus
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Copeland's Owl's-clover
Orthocarpus cuspidatus ssp. copelandii
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Cryptantha Owl's Clover
Orthocarpus cuspidatus ssp. cryptanthus
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Siskiyou Mountains Orthocarpus
Orthocarpus cuspidatus ssp. cuspidatus
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Mountain Owl's-clover
Orthocarpus imbricatus
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Yellow Owl's Clover
Orthocarpus luteus
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Shasta Orthocarpus
Orthocarpus pachystachyus
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Sweet Cicely
Osmorhiza berteroi
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California Sweetcicely
Osmorhiza brachypoda
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Bluntseed Sweetroot
Osmorhiza depauperata
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Mountain Sweet Cicely
Osmorhiza occidentalis
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Purple Sweetroot
Osmorhiza purpurea
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California Wood-sorrel
Oxalis californica
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Redwood Sorrel
Oxalis oregana
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Klamath Ruby Redwood Sorrel
Oxalis oregana 'Klamath Ruby'
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Smith River Redwood Sorrel
Oxalis oregana 'Smith River'
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Radishroot Woodsorrel
Oxalis pilosa
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Suksdorf's Wood-sorrel
Oxalis suksdorfii
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Threeleaf Woodsorrel
Oxalis trilliifolia
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Mountain Sorrel
Oxyria digyna