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Euphrasia

Individuals of Euphrasia are known to vary morphologically according to differences in nutrient supply, length of growing season, and height of surrounding vegetation (Downie  and McNeill 1990). Therefore, some characters used to discriminate species of Euphrasia   (e.g., internode length, number of nodes to first flower, number of branches), though  generally useful, can show tremendous variation and should be confirmed through use of additional characters. Sell and Yeo (1970) noted specimens from the Plantae Exsiccatae Grayanae (number 62) that may be referable to Euphrasia ×‌aequalis Callen ( E. nemorosa ×E. tetraquetra) from Frenchville, ME. Reference: Sell and Yeo (1970).

See list of 2 species in 1a
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1a. Bracts with subulate or bristle-tipped teeth [Figs. 751,752]; corolla 5–8 mm long
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  E. stricta
  2a. Bracts erect to ascending, cuneate at the base, with ascending teeth [Fig. 752]
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  E. nemorosa
  2b. Bracts ascending to spreading, rounded to truncate at the base, with spreading teeth [Fig. 751]
See list of 5 species in 1b
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1b. Bracts with obtuse to acute teeth; corolla 2.5–5 (–7.5) mm long
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  3a. Corolla 5–7.5 mm long
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    E. suborbicularis
    4a. Corolla white; stem leaf blades suborbicular to rhombic or obovate; capsules (4–) 5–6.5 mm long; floral leaf blades 5–15 mm long; flowering beginning from the 5th to the 9th node (rarely as low as the 2nd node)
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    E. micrantha
    4b. Corolla light purple; stem leaf blades ovate (rarely elliptic); capsules 4–5.5 mm long; floral leaf blades 4–8 mm long; flowering beginning from the 7th to the 11th node
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  3b. Corolla 2.5–5 mm long
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    E. oakesii
    5a. Calyx lobes obtuse at the apex and falcately curved; stems simple or rarely with 1 or 2 branches from the upper nodes; flowering beginning from the 4th or 5th node
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    5b. Calyx lobes acute at the apex and ± straight; stems usually with 1–4 (–5) branches from the middle and upper (rarely the lower) nodes or rarely simple; flowering beginning from the 3rd to the 8th node (rarely as high as the 10th node)
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      E. tetraquetra
      6a. Corolla 4–5 mm long, white, sometimes with a light purple upper lip; stem internodes shorter than to slightly longer than the associated leaves; capsules truncate at apex, not reaching tips of calyx lobes
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      E. randii
      6b. Corolla 2.5–4.5 mm long, light purple to purple (rarely white); stem internodes 1–3 times as long as the associated leaves; capsules retuse or emarginate at apex, as long as or exserted beyond the tips of the calyx lobes

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Show photos of: Each photo represents one species in this genus.