Axelrod: The Pliocene Verdi Flora of Western Nevada 119 



Merriam (1916, pp. 166-168), in his paper on the Cedar Mountain mammalian 

 fauna of south-central Nevada, reviewed the age relations of the Truckee and 

 Esmeralda formations from the fossil evidence then in hand. As a basis for this 

 discussion, Merriam turned over to Knowlton his small Verdi collection for study. 

 Knowlton (in Merriam, 1916) identified twelve species, of which six were con- 

 sidered to be present in the Esmeralda flora 130 miles southeast. From this pre- 

 sumed relationship with the Esmeralda, which was then regarded as Miocene, 

 Knowlton concluded the Verdi also was Miocene. The original list of twelve species 

 was not published by Merriam, and the fossils identified by Knowlton were not 

 labeled permanently, so it is not possible to evaluate his identifications with cer- 

 tainty. Nonetheless, a comparison of the six Esmeralda species with the Verdi 

 plants that Knowlton thought were similar, suggests that the following identifica- 

 tions may be more nearly correct: 



Knowlton's identifications 



~t ■&„„*■ „„„ „•„„ Present interpretation 



of Verdi species r 



Cercis? nevadensis? Knowlton Populus pliotremuloides Axelrod 



Chrysobalanus pollardiana Knowlton Populus alexanderi Dorf 



Ficus? lacustris Knowlton Populus alexanderi Dorf 



Ehus? nevadensis Knowlton Arctostaphylos verdiana Axelrod 



Salix angusta A. Braun Salix truckeana Chaney 



Salix sp. Knowlton Salix truckeana Chaney 



In any event, on the basis of my studies of both floras it is certain that not more 

 than one species (Populus pliotremuloides) was common to the collections exam- 

 ined by Knowlton. This is not surprising, for the Early Pliocene Esmeralda is 

 dominated by live oak woodland, chaparral, and desert-border vegetation (Axel- 

 rod, 1940), and would thus be expected to have but little in common with the Verdi. 



It was Chaney (1938&, p. 388) who was the first to express the opinion that the 

 Verdi flora was Pliocene. He noted that the rarity of forest species in the flora, and 

 the dominance of stream-border types in it, were consistent with a Pliocene age 

 assignment. 



The fossil plants comprising the Verdi flora not only demonstrate its Pliocene 

 age, but also afford critical evidence with respect to its position within the epoch. 

 The distribution of its woody plants in other floras in the far West is shown in 

 table 6. 5 Five identical and 5 related species are known from Miocene floras; 13 

 identical and 2 similar species have been recorded in transitional Mio-Pliocene 

 floras ; 5 identical and 4 related species are reported in the late Early Pliocene ; 8 

 identical and 2 related species are known in the Middle Pliocene ; and 7 identical 

 and 2 similar species have been recognized in Late Pliocene floras. Among the Mio- 

 Pliocene floras, closest relationship is apparent with the Chloropagus, Middlegate, 

 and Aldrich Station floras of western Nevada (Axelrod, 1956), each of which has 

 from 5 to 7 species in common with the Verdi. Pertinently, the Late Pliocene Napa 

 flora of California (Axelrod, 1950a) has as many species in common with the Verdi 

 as do these nearby Mio-Pliocene floras. 



5 Excluded from consideration are three aquatics (Chara, Nymphaeites, and Potamogeton) , 

 which have little age significance, and two of the new woody plants (Arctostaphylos verdiana and 

 Ribes galeana), which are now known only from the Verdi flora and do not have close relatives 

 in other floras. 



