11 



RHUS AND ITS ALLIES 

 By T. D. a. Cocker ell 



The old genus Rhus has at various times been divided to form 

 new genera. Authors to-day do not agree in their treatment of 

 it. Rhus and Cotinus are generally recognized, the former con- 

 taining very diverse elements. Dr. Small (Flora of the South- 

 eastern States) separates four genera, Cotinus, Rhus, Mctopium 

 and ScJiinaltda. Dr. Greene (Leaflets, 1905) calls Dr. Small's 

 ''Rhus,'' Toxicodendron, while part of his Schuialt.da is con- 

 sidered to be true Rhus. 



At first sight, the separation of so many genera may seem 

 questionable. In Dr. Small's table we find " Drupe with a gla- 

 brous outer coat ; stone ribbed," and " Drupe with a pubescent 

 outer coat; stone smooth," given as differential characters. 

 Why might not these differences arise all at once, by mutation, 

 in different series ? What proof is there that they imply a deep- 

 seated and fundamental segregation of types ? I have before me 

 a little piece of Ccanotlius vclutinus lacvigatus, T. & G., from 

 Ward, Colo., with many fruits. These are 3-lobed as usual, 

 except one, which is regularly and completely ^-lobed. Is not this 

 as good a difference as " drupe pubescent," and have we two 

 genera here on this one fragment of a single plant ? 



There are, however, other reasons for supporting the dismem- 

 berment oi Rhus. Judge J. Henderson and Dr. F. Ramaley, of 

 the University of Colorado, recently made an expedition to the 

 famous Tertiary beds of Florissant, Colorado, and brought back a 

 fine series of fossil plants. At Fossil Stump Hill, they obtained a 

 beautiful specimen of Rhus, which is now before me. It is the Rhus 

 coriarioides Lesquereux, Cret. and Tert. Floras, 193. 1883. It 

 is more perfect than the single specimen known to Lesquereux, 

 as the tips of most of the leaflets are preserved. It is so close to 

 Rhus hirta that there is little on which to separate it, beyond the 

 fact that the tips of the leaflets are more produced and tapering, 

 the distance from the last serration to the apex being about 16 

 mm., in a leaflet 60 mm. long. So it appears that away back in 

 the middle of Tertiary time the /^/r/^-group [Rlnts of Greene, part 



