164 



RUTACEAE. 



Ptelea. Hop Tree. 

 (Family Rutaceae). 



Shrubs or small trees: decidu- 

 ous. Twigs moderate, warty and 

 dotted, terete: pith rather large, 

 roundish, continuous, white. Buds 

 moderate, closely superposed in 

 pairs, very low-conical, sessile, 

 breaking through the leaf-scars, 

 not distinctly scaly, silvery-silky, 

 the end-bud lacking. Leaf-scars 

 alternate, somewhat raised, rather 

 large, horseshoe-shaped when torn 

 by the buds: bundle-traces 3: 

 stipule-scars lacking. 



Winter-characters: Ptelea tri- 

 foliata. Bosemann, 56; Brendel, 

 27, 30, pi. 3; Hitchcock (1), 4, 

 f. 3; Schneider, f. 97. 



To some persons, notwithstand- 

 ing its blue-green foliage, Ptelea 

 resembles Staphylea when grow- 

 ing, but its alternate leaves or 

 leaf-scars and very different buds afford a ready and sure 

 means of recognition. In winter it is much more likely to 

 be mistaken for Phellodendron. 



The importance of twig-characters, observance of which 

 need not be restricted to the winter months, is pointed out 

 by Greene in the tenth volume of Contributions from the 

 United States National Herbarium, where he segregates 59 

 nominal western and southwestern species of Ptelea, in addi- 

 tion to an earlier subdivision (Torreya, 5:100) of what is 

 here called P. trifolia. 



Twigs glabrous, buff. (Wafer ash). P. trifoliata. 



Twigs puberulent. P. trifoliata mollis. 



