452 MINNESOTA BOTANICAL STUDIES 



Analytical Key to Species and Hybrids 



I. Leaves 6-10 cm. long, mostly thin and papery, 6-12 pairs of veins; fruit- 

 ing catkins 3 cm. long or more ; trees 

 a. Fruiting catkins sessile or nearly so, erect, oblong-ovoid 11-18 mm. 

 thick; wing narrower than nutlet; leaves with 9-12 pairs of veins, 

 inner bark with wintergreen flavor, 

 m. Leaves oblong-ovate or ovate, sharply and evenly serrate ; bract 

 smooth and firm ; bark not peeling 



B. Icnta 

 n. Leaves ovate, mostly oblique at base, sharply doubly-serrate ; bract 

 ciliate-pubescent along the margins, thinnish ; bark peeling 



B. lutea 

 h. Fruiting catkins pedicelled, spreading or pendent, 8-10 mm. thick, wing 

 wider than nutlet; leaves with 6-9 pairs of veins, inner bark 

 without wintergreen flavor 



B. papyrifera 



n. Leaves 2-6 cm. long, thick and firm in texture, i-7 pairs of veins ; fruiting 

 catkins mostly less than 3 cm. long ; shrubs 

 a. Leaves ovate to broadly ovate or oval, 5-7 pairs of veins; fruiting 

 catkins oblong-ovoid, 1.5-2.8 cm. long, 10-13 mm. thick, short- 

 stalked or sessile; bracts 5.5-7 mm. long; twigs aromatic 

 m. Bracts about as broad as long, smooth or nearly so, samara obcor- 

 date, about 4 mm. broad 



B. lenta x 

 pmnila 

 n. Bracts longer than broad, lobes ciliate-pubescent along the margins, 

 samara obovate, about 3.4 mm. broad 



B. lutca X 

 pumila var. 

 glandulifcra 

 h. Leaves rhombic-ovate, obovate or oval, 3-5 pairs of veins ; fruiting 

 catkins cylindric or ovoid-cylindric, 5-7 mm. thick, distinctly pedi- 

 celled ; bracts 3-5.5 mm. long; twigs not aromatic 

 m. Leaves rhombic-ovate or obovate ; fruiting catkins 2-3 cm. long, 

 6-7 mm. thick; bracts 4-5.5 mm. long; wing as wide or wider 

 than nutlet ; tall shrub 



B. papyrifera x 

 piimila var. 

 glandulifera 

 n. Leaves obovate to oval ; fruiting catkins 1-2.8 cm. long, 5-6 mm. 

 thick; bracts 3-3.5 mm. long; wing of samara narrower than 

 nutlet, low or medium sized shrub 



B. pumila var. 



glandulifera 



JMote: B. lenta and the hybrid B. lenta x pumila are included in the key. together 

 with descriptions for the purpose of comparison. The writer is not aware that the latter 

 has been found in anv locality outside the Arnold Arboretum, and although B. lenta has 

 been reported from Minnesota, it is e-xtremely doubtful whether it occurs in the state. 



