Locality
Yukon-Koyukuk Basin Locality 11557
Description
Leaf: simple; symmetrical; wide to very wide obovate, trilobed; apices of lobes obtuse; base missing; margin dentate; teeth with obtuse rounded apices, convex to concave sides, shallow rounded sinuses; venation distinctly marginal perfect actinodromous; primary midvein moderate, straight; pectinal veins as strong as midvein, straight or nearly so, running to apices of lobes, departing midvein at 30-35°; branching admedially up to three times near lobe apex, admedial branches moderate, curved craspedodromous; abmedial veins moderate, curved, departing at 40-50°, craspedodromous or weakly semicraspedodromous; superior secondary veins moderate, curved, departing midvein at approximately 50°, craspedodromous, sometimes branched once or twice both ad- and abmedially near margin, more apical secondaries inwardly curving near margin, weakly semicraspedodromous; weak composite intersecondary and inter-abmedial veins present; tertiary veins moderate but variable in strength; percurrent, branched, usually meeting secondaries at approximately 90°; fourth order veins percurrent, orthogonal, or forming an orthogonal reticulum; ultimate marginal venation may be looped.
Remarks
This specimend undoubtedly represents a leaf which Hollick named Grewiopsis yukonensis (Hollick 1930; Plate 81, p. 107). Hollick compares his specimen to Grewiopsis acuminata Lesquereux (1887; Plate 3, Figs. 12, 13; Plate 4, Figs. 1, 2) and G. walcotti Lesquereux (1887; Plate 4, Figs. 3, 4) from his so-called 'Laramie' Formation of Utah which he considered were much the same except that his specimen was larger (18 cm x 18 cm). Such size differences are probably not valid as diagnostic characters because size is so greatly affected by environmental factors. Comparison should also be made with the later (Danian?) 'Viburnum' lakesii Lesquereux as figured in Knowlton (1917; Plate 110, Fig. 3).
