Oenothera biennis
 
Yellow Evening-Primrose

Upper Stem

Last Mountain Lake Regional Park
07-August-2010

This is from a branch of the inflorescence.

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Biennis: Answers to key questions in Budd's Flora and Flora of Alberta leading to this species. 
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plants with leafy stems; NOT [plants lacking leafy stems, leaves forming a rosette]

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plant usually NOT much-branched

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plants herbaceous; NOT [plants suffrutescent, usually with several slender stems]

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stems green or reddish; NOT [stems white, shreddy], NOT [plants with brown woody stems]

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stems taller; NOT [stems 3-10 cm tall]

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stems stout; NOT [stems slender]

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flower buds erect; NOT [flower buds nodding]

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flowers larger; NOT [flowers minute]

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petals more than 5 mm long; NOT [petals 1-3 mm long]

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flowers yellow; NOT [flowers white or pinkish]

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stigma deeply 4-cleft

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capsules rounded on the angles, not winged; NOT [capsules 4-angled, winged]

 

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Oenothera: Answers to key questions in Budd's Flora and Flora of Alberta leading to this genus. 
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hypanthium prolonged beyond the ovary

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flower parts in 4ís; NOT [flower parts in 2ís]

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sepals commonly reflexed; NOT [sepals erect]

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petals yellow, white or pink; NOT [petals purplish]

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anthers attached near their middle, usually versatile; NOT [anthers attached near their base, erect]

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ovary 4-loculed; NOT [ovary2-loculed]

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fruit a capsule; NOT [fruit nut-like]

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fruit opening by valves; NOT [fruit indehiscent]

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fruit opening with 4 valves; NOT [capsules opening with 2 valves]

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fruit NOT covered with hooks; NOT [fruit covered with hooked bristles]

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seeds lacking a coma; NOT [seeds with a tuft of hairs (coma) at one end]

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fruit many-seeded; NOT [fruit 1-seeded]

 

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Onagraceae: Answers to key questions in Budd's Flora  leading to this family. 
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herbs; NOT [shrubs or trees]

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plants terrestrial; NOT [plants aquatic; leaves submerged or floating], NOT [mud plants with small axillary flowers]

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plants NOT with colored milky juice

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plants with more than one normal leaf

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leaves without stipules, or having glands; NOT [leaves with stipules]

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plants without large petal-like bracts; NOT [plants with an involucre of 4 petal-like bracts]

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flowers with two floral rings, and with each petal distinct from the others]

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parts of flowers in twos or fours; NOT [parts of flowers mostly in fives]

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calyx regular; NOT [calyx irregular, some sepals smaller than others]

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stamens 10 or fewer; NOT [stamens usually more than 10]

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styles single; NOT [styles 2 or more]

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ovary inferior; NOT [ovary superior]