128 University of California Publications in Geological Sciences 



Family SALICACEAE 



Populus alexanderi Dorf 



(PI. 19, figs, l-ll) 



Populus alexanderi Dorf, Carnegie Inst. Wash. Pub. 412, p. 75, pi. 6, figs. 10-11 only; pi. 7, 

 figs. 2, 3 only, 1930; Chaney, Carnegie Inst. Wash. Pub. 476, p. 215, pi. 6, figs. 1, 5; pi. 7, 

 fig. 2, 1938; Axelrod, Carnegie Inst. Wash. Pub. 553, p. 281, pi. 48, fig. 4, 1944; Axelrod, 

 Carnegie Inst. Wash. Pub. 590, p. 199, pi. 4, fig. 6, 1950 ; Axelrod, Univ. Calif. Pub. Geol. Sci., 

 vol. 33, p. 282, pi. 6, fig. 9 ; pi. 13, figs. 1-2, 1956. 



The leaves of this cottonwood are so abundant at the Verdi locality they ac- 

 count for over 90 per cent of all the specimens examined. They are regularly small 

 and oval to ovate, or suborbicular, like leaves produced by the living Populus 

 trichocarpa Torrey & Gray in the warmer parts of its range at low to moderate 

 elevations in south-central and southern California. The related P. eotremuloides 

 Knowlton, which is common in the Miocene floras of the far West, has much larger, 

 lanceolate leaves, and they resemble those produced by the living black cottonwood 

 in the more humid and cooler sections of its range. 



Occurrence. — Verdi, Nev.: U.C. Mus. Pal. (loc. P102), hypotypes nos. 1979, 

 1982-1990, 2024. 



Populus pliotremuloides Axelrod 

 (PI. 22, figs. 5-8) 



Populus pliotremuloides Axelrod, Carnegie Inst. Wash. Pub. 476, p. 168, pi. 4, figs. 1-3, 1937 ; 

 Axelrod, Carnegie Inst. Wash. Pub. 553, p. 281, pi. 48, fig. 6, 1944; Axelrod, Carnegie Inst. 

 Wash. Pub. 590, p. 53, pi. 2, fig. 4, 1950 ; Axelrod, Univ. Calif. Pub. Geol. Sci., vol. 33, p. 284, 

 pi. 25, fig. 10, 1956. 



The small characteristic leaves of aspen are rather common in the Verdi flora. 

 They are typically oval to orbicular, with margins ranging from entire to finely 

 crenate. The leaves of P. subwashoensis, which may be confused with them, differ 

 in having relatively larger and fewer dentate teeth. 



Occurrence. — Verdi, Nev.: U.C. Mus. Pal. (loc. P102), hypotypes nos. 1998- 

 2001; homeotypes nos. 2002-2004. 



Populus subwashoensis Axelrod 

 (PL 22, figs. 1-4) 



Populus subwashoensis Axelrod, Univ. Calif. Pub. Geol. Sci., vol. 33, p. 284, pi. 6, figs. 1-4; pi. 13, 



figs. 3-4; pi. 18, fig. 5, 1956. 

 Populus pliotremuloides Axelrod. Chaney, Carnegie Inst. Wash. Pub. 476, p. 214, pi. 6, fig. 4 ; 



pi. 7, figs, lc, Id, 1938. 

 Populus washoensis Brown. Axelrod, Carnegie Inst. Wash. Pub. 553, p. 131, 1944. 



The small leaves of this poplar are relatively common in the Verdi flora. The 

 leaf margins are characterized by large dentate teeth as compared with P. plio- 

 tremuloides, which ranges from entire to finely crenate. 



Among living species, P. subwashoensis resembles the smaller leaves of P. 

 grandidentata Michaux of the northeastern United States and adjacent Canada. 

 However, leaves of the east Asian P. tremula davidiana Schneider, which ranges 



