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Key to Linum

Linaceae

Linum

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1 Petals blue, red, or pink (rarely white); capsule 5-10 mm long; [section Linum].
  2 Petals blue (rarely white).
    3 Inner sepals with minutely ciliate margins; stigmas slender, elongate; capsule 6-10 mm long
      4 Flowers heterostylous (some flowers with stigmas below the anthers, others with stigmas well above the anthers)
      4 Flowers homostylous (flowers with stigmas at about the level to slightly above the anthers)
1 Petals predominantly light to dark yellow (sometimes also with other coloration, including orange, copper, salmon, brown, and red bands or blotches); capsules 1-4 mm long; [section Linopsis].
          6 Outer sepals entire (very rarely sparsely glandular-toothed), the inner sepals entire or sparsely to conspicuously glandular-toothed; leaves without red or brown stipular glands flanking the attachment to the stem.
             7 Fruit as long as broad or longer, its apex acute, apiculate, or obtuse, (2-) 2.2-3.2 (-3.3) mm long; leaves mostly 1.3-4.3 mm wide.
               8 Leaves opposite; fruit subspherical, abruptly short-pointed
               8 Leaves all or mostly alternate (a few pairs of leaves at the base of the stem sometimes opposite); fruit ovoid to pyriform.
                 9 Leaves (1.2-) 2.3-4.3 (-5.6) mm wide, mostly 25-50 below the inflorescence; septa of the fruit sparsely but conspicuously ciliate; false septa incomplete; fruit apex acute, the exposed portions purple
                 9 Leaves (1.0-) 1.3-2.0 (-3.2) mm wide, mostly 50-165 below the inflorescence; septa of the fruit glabrous; false septa virtually complete; fruit apex rounded to apiculate, the exposed portions purple or yellow.
                   10 Fruit 3.4-3.8 mm long, 3.2-3.4 mm in diameter
                   10 Fruit (2.0-) 2.3-3.2 (-3.3) mm long, 1.7-3.1 mm in diameter.
                     11 Fruit ovoid, (2.8-) 3.0-3.2 (-3.3) mm long, 2.5-3.1 mm in diameter, the apex minutely apiculate, the exposed portions yellow; seeds 2.1-2.4 mm long; anthers averaging 1.2 mm long
                     11 Fruit pyriform, (2.0-) 2.3-2.8 (-3.0) mm long, 1.7-2.6 mm in diameter, the apex rounded, the exposed portions purple; seeds (1.6-) 1.7-2.0 (2.1) mm long; anthers averaging 0.8 mm long
             7 Fruit broader than long, its apex depressed, flattened, or broadly rounded, (1.3-) 1.5-2.1 (-2.3) mm long; leaves mostly 1.9-9.3 mm wide.
                       12 Margins of the inner sepals with conspicuous stalked glands (these few or even absent in L. medium); mature fruits of dried specimens usually adhering to the plant.
© Scott Ward
                          13 Inner sepals conspicuously glandular-toothed; leaf apices minutely apiculate (and translucent); leaves relatively translucent, [widespread in our region]
                          13 Inner sepals sparsely glandular-toothed (or entire); leaf apices obtuse, opaque; leaf blade relatively opaque; [questionably present in n. PA northwards]
                       12 Margins of the inner sepals glandless, or with a few inconspicuous, sessile glands; mature fruits of dried specimens usually shattering and falling freely.
                            14 Styles distinct (free); [collectively widespread in our region].
(c) Fleming, Gary P.
                              15 Inflorescence paniculate, the lower inflorescence branches not elongate, their tips not nearly reaching the tips of the upper inflorescence branches; branchlets striate-ridged; leaves mostly opposite (usually to beyond the midpoint from the base of the plant to the first inflorescence branch)
                              15 Inflorescence corymbose, some (at least) of the lower branches of the inflorescence elongate, their tips nearly equaling the tips of the upper inflorescence branches; branchlets terete or nearly so; leaves mostly alternate (usually the opposite leaves of the lower stem not extending beyond the midpoint from the base of the plant to the first inflorescence branch)
                            14 Styles connate (united basally); [west of the Mississippi River, in LA, OK, and TX].
          6 Inner and outer sepals all very conspicuously glandular-toothed; leaves with 2 red or brown stipular glands flanking the attachment to the stem (these absent or obscure in L. smallii and L. rigidum var. rigidum – but check leaves on the upper and lower stem).
                                         20 Sepals 2.3-3.5 mm long, acute; inflorescence consisting of 1 or more elongate and racemiform branches; dried plants dark, purple-dotted; [Coastal Plain of FL Panhandle]
                                         20 Sepals (3.1-) 3.6-5 (-7.3) mm long, acuminate; inflorescence an open panicle; dried plants pale green; [widespread, mainly inland provinces except westwards]
                                                      26 Stem puberulent or scabrous on the angles throughout; plants (11-) 17-28 (-33) cm tall; petals 9-11 mm long; styles 4.4-6.1 mm long; stipular glands present
                                                      26 Stem glabrous (or sometimes sparsely puberulent or scabrous near the base); plants (17-) 28-45 (-64) cm tall; petals 11.5-17 mm long; styles 5.1-9.1 mm long; stipular glands usually absent or essentially so