Locality
USGS 11613
Lat. 60° 33' 32"N Long. 165° 24' 16"W
Nunivak Island (C-1) Quad.
Description
Leaf: simple; symmetrical; wide obovate; apex missing; base decurrent; margin dentate except in the basal quarter of the leaf where it is entire, teeth irregular in size and spacing, apices angular acute or obtuse, sinuses rounded; venation suprabasal marginal perfect actinodromous or weakly palinactinodromous; primary midvein moderate, more or less straight; pectinal veins moderate to weak, more or less straight or slightly curved arising at an angle of 30-35°; pectinal abmedials arising at an angle of 25-30°, more or less straight, but may be slightly curved often branched, the basal abmedial also branched abmedially at an angle of 30-35° to form weak b-pectinals; superior secondary veins arising from the midvein at an angle of 35-40°, slightly curved, often branching near the margin, moderate craspedodromous; tertiary veins percurrent, convex, sometimes sinuous, often forked joining both ad- and abmedial sides of the secondary at an acute angle of more or less 90°, rarely obtuse; fourth order veins not visible.
Remarks
The weak palinactinodromy is particularly marked in this specimen and it belongs to the diverse group of 'platanoid' hamamelids that were widespread in Late Cretaceous time. Although the margin is not well preserved it seems to be inflated or slightly lobed in the region where the pectinals terminate. Leaves with this form and architecture have been given numerous names which Brown combined into a single species 'Cissus' marginata (Brown, 1962, p. 79-81). If Brown's combination is an accurate reflection of the true relationship of these leaves which have been, as Brown points out, assigned to alders, birches, maples, grapes, sycamores and viburnums, then the specimen figured here may be part of a compound leaf. Brown considered Winchellia triphylla Lesquereux (1892, p. 209; Plate 8, Fig. 1) to be the same as 'Platanus'? newberryana as figured in Hollick (1930; Plate 46, Fig. 2) to which this specimen bears a striking resemblance. W. triphylla is a trifoliate compound leaf and Brown (1962) states that at all localities where the characteristic terminal leaflets are found (the terminal leaflets are those which are similar in form to specimen USGS 11613.3) the asymmetric forms of variable shape and size which represent the lateral leaflets also occur. It is the variable nature of these presumed lateral leaflets that is the basis for Brown's extensive (64 species) synonymy. However, Brown admits that " *** many of the figured single leaves, purporting to have been terminal leaflets, may in reality have been simple leaves, for they show no evidence of leaflet scars on their long petioles" (Brown, 1962, p. 80).
Brown did not recognize the palinactinodromous venation and described the leaves as fundamentally pinnate. This coupled with the supposed compound nature of the leaves, led him away from considering these forms to represent an extinct relative of 'Platanus'. He could find " *** no compound specimens of living Platanus seedlings, suckers, or shoots that could be regarded as possible atavistic throw-backs".
In combining so many diverse forms from rocks of Late Cretaceous and Paleocene age Brown may well have obscured distinctions between some biostratigraphically useful forms.