MINNESOTA TREES AND SHRUBS 



(b) Leaves somewhat oblong, much longer than 

 broad 

 x. Leaves opposite Viburnum : black haw 280 



y. Leaves both opposite and alternate, per- 

 sistent in autumn Rhamnus: buckthorn 197 

 z. Leaves alternate 



(x) Leaves two-ranked, or apparently so 

 m. Sap milky; small trees Morus; mulberry 79 



n. Sap not milky 



(m) Leaves with one distinct midvein 

 r. Bark smooth, except when very old, 



splotched Carpinus : hornbeam 243 



s. Bark rough 



(r) Leaves very oblique at base; 



bark coarsely furrowed Ulmus : elm 73 



(s) Leaf base not oblique ; bark 



finely furrowed Ostrya : ironwood 245 



(n) Leaves with three large veins at 



base; bark ridged Celtis: hackberry 77 



(y) Leaves not two-ranked 

 m. Bark with long conspicuous lenticels Betula : birch 246 



n. Bark without conspicuous lenticels 

 (m) Leaves doubly serrate or toothed 

 r. Stems and twigs more or less thorny Crataegus: hawthorn 154 



s. Stems and twigs without thorns Malus: apple 159 



(n) Leaf margin with a single row of 

 teeth 

 r. Buds small, scales overlapping, 



many; fruit fleshy Prunus: plum, cherry 163 



s. Buds larger, covered by a single 



scale ; fruit dry Salix : willow 59 



(2) Leaves lobed 



(a) Leaves opposite Acer: maple 219 



(b) Leaves alternate or fascicled 



x. Leaves fan-shaped, many of them fascicled Ginkgo : maiden-hair tree 43 



y. Leaves neither fan-shaped nor fascicled 



(x) Leaves two-ranked Morus : mulberry 79 



(y) Leaves more than two-ranked 

 m. Leaves deeply cut-lobed ; bark white 

 (m) Leaves small, bark separating into 



papery layers Betula : birch 246 



(n) Leaves silvery beneath, bark not 



papery Populus: poplar 53 



n. Leaves less lobed ; bark not white 

 (m) Leaf margin toothed 

 r. Stems and twigs thorny Crataegus: hawthorn 154 



s. Stems and twigs not thorny Malus: apple 159 



(n) Leaf margin entire Quercus: oak 257 



b. Leaves compound 



(1) Leaves palmate 



(a) Leaflets 3 Ptelea: hoptree 82 



(b) Leaflets many Aesculus: horse chestnut 216 



(2) Leaves pinnate 



(a) Leaves even-pinnate 



x. Leaves twice-compound 



(x) Leaves 3-9 dm. long; leaflets ovate Gymnocladus: coffee tree 172 



(y) Leaves 1-2J4 dm. long; leaflets oblong Gleditsia: honey locust 173 



y. Leaves once-compound Caragana: pea-tree 179 



(b) Leaves odd-pinnate 

 x. Leaves opposite 



(x) Leaflets entire or finely serrate Fraxinus: ash 107 



