60 



American Midland Naturalist Monograph No. 4 



Fig. 15. California filbert (Cor\)lus roslrala 

 var. calif ornica) . 



Fig. 16. Knowlton hophornbeam 

 (^Oslr\)a Knotelloni). 



in moist wooded sections, 3,500 to 7,500 feet: Clough Cave; east of Colony Peak; 

 1 ocopah Falls ; Bearpaw Meadow. 



Knowlton Hophornbeam (Ostrya Knowltoni Gov.), fig. 16. — Shrubs, 

 or slender trees up to 12 feet high, with ashy-gray bark; leaves egg-shaped to 

 elliptic, pointed or rounded at the tips, 1 to 2 inches long, soft-hairy below, 

 the margins sharply double-toothed; flowers appearing with the leaves, the 

 staminate in slender drooping catkins, the seed-bearing in small inconspicuous 

 clusters; fruits small nutlets, each enclosed by a yellow-green or straw-colored 

 bladdery sac and forming clusters similar to that of the hop. 



Hophornbeam might easily be mistaken for a birch or for beaked filbert 

 by one unfamiliar with the genus, but the fruits are entirely different. They 

 are small flattened nutlets, each surrounded by a loose, papery, bladder-like 

 sac. These are clustered into small heads at the ends of short nodding stems. 

 Like the birches, the foliage turns yellow in the autumn. 



Occurrence. — grand canyon, occasional in the canyon, 4,500 to 7,000 feel: Kaibab 

 trail 11/2 miles below Yaki Point; Roaring Springs canyon; Bright Angel trail. 



American Hophornbeam (Ostrya virginiana (Mill.) Koch.) is reported 

 from Greenstone Ridge on Isle Royale. This differs from Knowlton hophorn- 

 beam in being in general larger with long-pointed leaves 2i^ to 4 inches long 

 and with the fruit clusters larger. 



