Acer L.

1. Acer L. 1

Trees or shrubs, usually deciduous. Leaves long-petiolate, usually palmately lobed. Flowers greenish or yellowish, often unisexual, sometimes apetalous. Samarae winged on outer side only.

Literature: F. Pax in Engler, Pflanzenreich 8 (IV. 163): 6-80 (1902). A. I. Pojarkova, Acta Inst. Bot. Acad. Sci. URSS 1: 225-374 (1933).

Two North American species, A. saccharophorum C. Koch, Hort. Dendrol. 80 (1853) ( A. saccharum auct.), and A. saccharinum L., Sp. Pl. 1055 (1753) ( A. dasycarpum Ehrh. ) are planted locally for timber in C. Europe. A. saccharophorum has leaves rather like those of 1, but paler beneath and without latex. A. saccharinum has leaves more deeply lobed and silvery-white beneath, also without latex.

1 Leaves pinnately 3- to 7-foliolate 15. negundo 1 Leaves simple, sometimes deeply palmately lobed 2 Leaves less than 8 cm, ± coriaceous 3 Wings of fruit horizontal; leaves cibate 3. campestre 3 Wings of fruit subparallel or diverging at an acute angle;

leaves not cibate 4 Leaves glabrous and green beneath, evergreen 14. sempervirens 4 Leaves pubescent or subglaucous beneath, deciduous 5 Leaves 3-lobed; lobes usually entire 13. monspessulanum 5 Leaves (3-)5-lobed; lobes dentate (8-12). opalus group 2 Leaves up to 15 cm, not coriaceous 6 Leaves undivided (rarely slightly 3-lobed) 4. tataricum 6 Leaves distinctly 3- to 7-lobed 7 Middle lobe of leaf separated nearly to base 6. heldreichii 7 Leaf lobed to not more than j of distance to base 8 Inflorescence paniculate; petioles without latex

9 Inflorescence erect, broadly pyramidal; leaves irregularly

dentate 7. trautvetteri

9 Inflorescence pendent, narrow; leaves serrate

5. pseudoplatanus 8 Inflorescence corymbose; petioles with or without latex

10 Petioles without latex; wings of fruit diverging at an

acute angle (8-12). opalus group

10 Petioles with latex; wings of fruit diverging at an obtuse

angle, sometimes nearly horizontal

11 Leaves usually less than 7 cm, cibate 3. campestre

11 Leaves (5—)7—15 cm, not cibate

12 Leaf-lobes almost entire 2. lobelii

12 Leaf-lobes sinuate-dentate 1. platanoides