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Group 4: Woody angiosperms with opposite or whorled leaves
See list of 24 families in this group-
1a. Plants 5–30 mm tall, parasitic on Picea, Larix, and Pinus [Fig. 939]; anthers sessile
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1b. Plants much taller or longer at maturity, not parasitic; anthers with filaments
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2a. Leaves compound
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3a. Fruit an inflated, thin-walled capsule with 3 lobes [Fig. 917]; gynoecium with 3 styles that are basally distinct and apically coherent
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3b. Fruit otherwise; gynoecium with 1 style that is often terminated by a lobed or branched stigmatic surface
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4a. Perianth zygomorphic; fruit a capsule
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5a. Plants trees with palmately compound leaves; capsule 3–5 cm long (in part)
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5b. Plants lianas with pinnately compound leaves; capsule 10–15 cm long (in part)
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4b. Perianth actinomorphic or absent; fruit an achene, schizocarp, drupe, or samara
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6a. Plants lianas (though woody only near base); flowers with numerous stamens; fruit an achene terminated by an elongate, plumose style [Fig. 812] (in part)
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6b. Plants upright shrubs or trees; flowers with 2–12 stamens; fruit otherwise
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7a. Leaflets punctate with aromatic glands; winter buds naked, enclosed by petiole base (in part)
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7b. Leaflets not punctate; winter buds covered by scales, not enclosed in petiole base
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8a. Fruit a samaroid schizocarp; ovary bilobed, compressed; androecium composed of 4–12 stamens, commonly 8 (in part)
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8b. Fruit a samara or drupe; ovary not bilobed, not compressed; androecium composed of 2 or 5 stamens
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9a. Perianth absent; androecium composed of 2 stamens; fruit a samara; flowers usually unisexual; trees at maturity (in part)
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9b. Perianth present and gamopetalous; androecium composed of 5 stamens; fruit a drupe; flowers bisexual; shrubs at maturity (in part)
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2b. Leaves simple
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10a. Apical portions of the stem succulent; leaves minute and scale-like, 1–3 mm long [Fig. 339]; stems appearing jointed; plants of Atlantic coast shores (in part)
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10b. Apical portions of the stem herbaceous to woody; leaves with foliaceous blades, mostly longer; stems not appearing jointed; plants of inland habitats
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11a. Leaves and leaf scars whorled
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12a. Perianth zygomorphic; fruit a slender, elongate capsule 20–45 cm long; seeds winged, the wings terminating in hairs (in part)
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12b. Perianth actinomorphic; fruit an achene-like schizocarp or a subglobose capsule 0.4–0.7 cm long; seeds without prominent wings
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13a. Inflorescence a cyme [Fig. 714]; flowers each with 8 or 10 stamens; petals pink-purple, 10–15 mm long; stems woody in the basal portion, surrounded by loose, spongy tissue, the buds barely emerging through the tissue (in part)
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13b. Inflorescence a dense, spherical cluster [Fig. 874]; flowers each with 4 stamens; petals white, 5–8 mm long; stems woody throughout, not surrounded by spongy tissue, the buds clearly visible (in part)
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11b. Leaves and leaf scars opposite
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14a. Leaves and branchlets conspicuously white- and/or brown-lepidote [Fig. 605]; plants dioecious (in part)
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14b. Leaves and branchlets without abundant scales; plants synoecious, polygamous, or dioecious
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15a. Leaf blades 6–15 mm long, crowded and imbricate [Fig. 615]; pulvinate plants of exposed, alpines areas above 1000 m elevation (in part)
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15b. Leaf blades longer than 20 mm, not crowded; plants of lower elevation habitats (except sometimes Viburnum edule)
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16a. Inflorescence a capitulum; fruit a resin-dotted cypsela (in part)
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16b. Inflorescence not pseudanthial; fruit a schizocarp, capsule, follicle, berry, or drupe, or 10–35 achenes enclosed in a fleshy hypanthium
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17a. Perianth of 15–30 brown-purple tepals; gynoecium with 10–35 carpels; androecium with 10–20 stamens and 10–25 staminodes seated inside the cycle of stamens
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17b. Perianth with fewer petaloid segments; gynoecium with 1–5 carpels; androecium otherwise, mostly with fewer stamens
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18a. Inflorescence mixed (i.e., thyrsoid), the indeterminate axis bearing cymose lateral branches, lateral branches manifesting as dense verticillasters of 6–10 flowers; fruit a schizocarp, separating into 4 achene-like mericarps; foliage pleasantly fragrant (in part)
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18b. Inflorescence not thyrsoid (appearing thyrsoid in Decodon, but then each cyme subtended by foliage leaves); fruit a capsule, follicle, or drupe, or a schizocarp in Acer that splits into 2 samara-like mericarps; foliage not especially fragrant
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19a. Stems woody only in the basal portion and surrounded by loose, spongy tissue, the buds barely emerging through the tissue; stamens dimorphic, of 2 different lengths (in part)
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19b. Stems woody ± throughout, not surrounded by spongy tissue, the buds clearly visible; stamens monomorphic
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20a. Fruit a samaroid schizocarp; ovary bilobed and compressed (in part)
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20b. Fruit a capsule, follicle, or drupe; ovary not, or inconspicuously, lobed, not compressed
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21a. Flowers without perianth; fruit a follicle
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21b. Flowers with perianth; fruit a capsule, berry, achene, or drupe
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22a. Perianth 5-merous
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23a. Corolla 50–70 mm long; ovary superior; fruit a capsule 30–40 mm long; seeds winged
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23b. Corolla 3–50 mm long; ovary inferior; fruit a drupe, berry, or achene, or a capsule 8–15 mm long; seeds without evident wings
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24a. Flowers with 8 or 10 stamens; corolla apopetalous (in part)
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24b. Flowers with 4 or 5 stamens; corolla gamopetalous
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25a. Style absent or very short; corolla of fertile flowers actinomorphic, white, 4–8 mm long (some species with sterile, enlarged, marginal flowers) (in part)
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25b. Style elongate; corolla actinomorphic or zygomorphic, white, pink, yellow, red, or purple, 3–50 mm (in part)
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22b. Perianth 4-merous
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26a. Leaf blades sessile, punctate with pellucid dots; petals yellow (in part)
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26b. Leaf blades petiolate (though the petioles sometimes short), lacking pellucid dots; petals white, yellow, green-white, blue, or brown-purple
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27a. Flowers with 2 or 4 stamens
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28a. Corolla gamopetalous
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29a. Flowers with 4 stamens; leaf blades white-tomentose on the abaxial surface (in part)
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29b. Flowers with 2 stamens; leaf blades glabrous or pubescent on the abaxial surface, but not white-tomentose (in part)
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28b. Corolla apopetalous
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30a. Fruit a drupe; leaf blades with arcuate venation; styles present; branches terete (in part)
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30b. Fruit a capsule; leaf blades not with arcuate venation; styles absent; branches often ± quadrangular (in part)
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27b. Flowers with 5–many stamens; corolla apopetalous
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31a. Petals yellow; leaf blades sessile and pellucid-punctate (in part)
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31b. Petals white, brown-purple, green-white, or ± yellow in Euonymus alatus; leaf blades petiolate (though the petioles sometimes short), without pellucid dots
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32a. Fruit a drupe; leaf blades entire, with arcuate venation [Fig. 594] (in part)
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32b. Fruit a capsule; leaf blades toothed, with pinnate venation (in part)
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Each photo represents one family in this group.