| 1 |
Evergreen trees; samaras strongly asymmetric, orange-brown. |
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20 U. lanceifolia |
| + |
Deciduous trees; samaras symmetric or weakly asymmetric, tan, light brown, pale green, or whitish (rarely slightly orange- or red-brown in U. macrocarpa and U. parvifolia). |
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(2) |
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| 2 (1) |
Flowers and fruit appearing late summer to early autumn. |
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21 U. parvifolia |
| + |
Flowers and fruit appearing in spring. |
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(3) |
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| 3 (2) |
Inflorescences racemose cymes or short cymes; peduncle slightly elongated to very noticeably elongated, pendulous; pedicel 2-4 × as long as perianth. |
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1 U. elongata |
| + |
Inflorescences fascicled cymes or fasciculate; peduncle extremely short, not pendulous; pedicel almost as long as or rarely longer than perianth. |
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(4) |
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| 4 (3) |
Seed at center or toward apex of samara; seed apex reaching notch (apex sometimes only nearly to notch in U. glaucescens). |
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(5) |
| + |
Seed at center or slightly toward base of samara; seed apex not reaching notch (apex sometimes near to notch in U. pumila). |
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(12) |
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| 5 (4) |
Flowers developed from mixed buds thus samaras usually on short shoots with one or a few leaves; leaves 1-3 cm wide, both surfaces pubescent or subglabrous, often with tufts of hairs abaxially in forkings of secondary veins (never in vein axils); samara wings relatively thick; seed broader than wings. |
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12 U. glaucescens |
| + |
Flowers developed from floral buds thus no leaves attached within each cluster of samaras; leaves 1.5-10 cm wide, variously pubescent or glabrous but often with tufts of hairs abaxially in vein axils (never in forkings of secondary veins); samara wings thin; seed narrower than wings. |
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(6) |
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| 6 (5) |
Samara ± pubescent. |
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13 U. chenmoui |
| + |
Samara glabrous except for notch or pubescent only on seed. |
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(7) |
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| 7 (6) |
Leaf blade abaxially densely pubescent. |
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19 U. castaneifolia |
| + |
Leaf blade abaxially glabrous or sparsely pubescent. |
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(8) |
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| 8 (7) |
Branchlets densely pubescent. |
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18 U. androssowii var. subhirsuta |
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Branchlets glabrous or sparsely pubescent. |
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(9) |
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| 9 (8) |
Samara obovate to ± obovate or oblong-elliptic to oblong-obovate. |
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(10) |
| + |
Samara ± orbicular to ovate-orbicular. |
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(11) |
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| 10 (9) |
Samara obovate to ± obovate; branchlets sometimes with a corky layer. |
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14 U. davidiana |
| + |
Samara oblong-elliptic to oblong-obovate; branchlets without a corky layer. |
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15 U. prunifolia |
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| 11 (9) |
Samara 7-8 × 7-8 mm; leaf blade 8.5-17 cm; petiole ca. 5 mm. |
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16 U. microcarpa |
| + |
Samara 11-16 × 9-13 mm; leaf blade 2-9 cm; petiole 5-12 mm. |
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17 U. szechuanica |
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| 12 (4) |
Samara pubescent. |
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(13) |
| + |
Samara glabrous or pubescent only on stigmatic surface. |
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(16) |
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| 13 (12) |
Leaf blade abaxially glabrous and ± scabrous, adaxially sparsely pubescent when young but glabrescent, margin serrate with acute teeth; bud scales glabrous. |
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5 U. changii |
| + |
Leaf blade abaxially ± pubescent and scabrous or not, adaxially scabrous and densely hirsute, margin rounded serrate; bud scales ± pubescent. |
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(14) |
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| 14 (13) |
Flowers developed from mixed buds; bark irregularly exfoliating, gray to grayish white. |
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4 U. lamellosa |
| + |
Flowers developed from floral buds or mixed buds; bark longitudinally fissured, gray to blackish gray. |
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(15) |
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| 15 (14) |
Branchlets pubescent; leaf blade apex obtuse-acuminate to acute; samara 1.8-2.8 × 1.7-2.7 cm. |
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2 U. gaussenii |
| + |
Branchlets glabrous or sparsely pubescent; leaf blade apex acuminate or shortly caudate; samara 1.5-4.7 × 1-3.9 cm. |
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3 U. macrocarpa |
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| 16 (12) |
Leaf blade apically 3-7-lobed; pedicel glabrous. |
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6 U. laciniata |
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Leaf blade apically not lobed; pedicel pubescent. |
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(17) |
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| 17 (16) |
Leaf blade 5-18 × 3-8.5 cm, apically narrowly acuminate to caudate; winter buds glabrous or variously pubescent. |
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(18) |
| + |
Leaf blade 2-8 × 1.2-3.5 cm, apically acuminate to cuspidate; winter bud scale margin usually white-ciliate. |
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(20) |
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| 18 (17) |
Winter buds ± pubescent, margin of bud scales prominently long ciliate; twigs sometimes conspicuously winged; samaras 1.5-4.7 × 1-3.9 cm. |
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3 U. macrocarpa |
| + |
Winter buds finely and inconspicuously puberulent, margin of bud scales entire or inconspicuously short-ciliate; twigs never winged; samaras 1-1.8 × 0.8-1.6 cm. |
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(19) |
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| 19 (18) |
Leaf blade 5-11 × 3-4.5 cm, abaxially pubescent, base ± oblique to ± symmetric; secondary veins 11-20 on each side of midvein; samara 8-10 mm wide. |
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8 U. uyematsui |
| + |
Leaf blade 6-18 × 3-8.5 cm, abaxially glabrous or pubescent, base distinctly oblique; secondary veins 17-26 on each side of midvein; samara 10-16 mm wide. |
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7 U. bergmanniana |
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| 20 (17) |
Leaf blade pubescent; petiole pubescent; samara wings relatively thick. |
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11 U. pseudopropinqua |
| + |
Leaf blade smooth and glabrous or with tufts of hair in vein axils; petiole glabrous or pubescent; samara wings relatively thin. |
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(21) |
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| 21 (20) |
Leaf blade margin simply serrate or sparsely doubly serrate; base symmetric to ± oblique. |
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9 U. pumila |
| + |
Leaf blade margin doubly serrate; base oblique. |
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10 U. harbinensis |
