Locality
Yukon-Koyukuk Basin Locality 11559
Description
Leaf: simple; symmetrical (?); wide obovate; apex missing; base decurrent; margin dentate, basal margin entire; teeth simple, more or less regular in size and spacing, apices obtuse to acute, non-glandular (?), sides concave, sinuses wide rounded; venation perfect, marginal, suprabasal actinodromous; primary midvein straight, moderate to stout; pectinal veins suprabasal, moderate, straight or slightly uniformly curved, departing the midvein at 34-40°; pectinal abmedial veins moderate, departing at angles of 35-40°, initially straight or slighly uniformly curved, becoming abruptly curved near margin to form irregular brochidodromous loops, branches may arise abmedially from the loops to join other loops or terminate in the apices of marginal teeth (semicraspedodromous); inter-abmedial veins present; superior secondary veins arising from the midvein parallel to the pectinals moderate, opposite near base, becoming alternate, straight or slightly and irregularly curved; inferior secondary veins weak, one to two pairs, slightly recurved, brochidodromous; tertiary veins somewhat irregular, percurrent, convex, moderate, simple or forked, departing abmedial sides of secondary veins at right angles, joining admedial sides predominantly at acute angles; fourth and higher order veins distinct, poorly differentiated, orthogonal percurrent to reticulate.
Remarks
These specimens are very closely allied to specimens USGS 11550.2, USGS 11559.2, USGS 11561.21, and USGS 11572.1 (form HAPLD26) but differ in that they display pronounced brochidodromy, albeit irregular, of the pectinal abmedial veins. The venation supplying the Platanoid teeth is semicraspedodromous. The incomplete nature of many specimens of this type, including those assigned to form HAPLD26, means that often the behaviour of the abmedials near the margin cannot be determined. For this reason these two groups of specimens have been described separately.
Brochidodromy is common in the basal pectinal abmedial veins of many mid-Cretaceous forms assigned to the genus 'Platanus'. A number of leaves reported by Hollick (1930) from the Yukon River localities possess this feature (for example, 'P.' latior (Lesquereux) Knowlton, 'Platanus'? sp.; 'P'. grewiopsoides Hollick, but do not exhibit it to the same degree as specimens USGS 11556.17 and USGS 11559.3.