Monographs Details: Platanus pseudoccidentalis
Authority: Hollick, Charles A. 1927. The Flora of the Saint Eugene Silts, Kootenay Valley, British Columbia. Mem. New York Bot. Gard. 7: 389-428.
Family:Platanaceae
Description:Species Description - Leaves trilobate, 20 to 23 centimeters in length by about the same in width; nervation 3-palmate, the lateral primaries supra-basilar, spreading; margin apparently sparingly and coarsely toothed, apparently developed below into a basilar appendage or alate border to the petiole.

Discussion:

PLATE 40; PLATE 41; PLATE 42

"Platanus n. sp." Hollick, Summary Kept. (loc. cit.), p. 135.

These leaves, which are abundantly represented in the collection, are surficially indistinguishable from those of the existing sycamore, Platanus occidentalis Linnaeus, of the Eastern United States. They are larger than the average-sized leaves on mature trees, but many individual leaves might be selected that would equal or exceed our specimens in size. The original specimens upon which the generic determination was based, are represented by the two figures, on PLATES 41 and 42, respectively. Specimens that have been referred to P. occidentalis may be found described in a number of different papers that are concerned with Pleistocene deposits in various parts of North America. The species, or forms closely allied to it, appear to have been as abundantly represented and as characteristic of the Pleistocene flora as were species of Fagus identical with or closely allied to F. grandifolia, and the several species of Hicoria. A number of specimens, from Pleistocene deposits in Alabama and North Carolina, were described and figured by Berry; 31 and specimens that are apparently specifically identical with the latter, from the Pleistocene (Sunderland formation) of Maryland, were figured and referred by the writer32 to Platanus aceroides Goeppert. All of these, however, are much smaller in size than are those from the Saint Eugene silts, but otherwise they are closely similar. Platanus aceroides Goeppert, as originally described and figured, was based upon specimens from the Miocene of Silesia; but subsequently a considerable diversity of forms, from both the New World and the Old, and ranging in age from the Eocene to the Miocene, and possibly Pliocene, were referred to the species by various authors. Certain of these forms are undoubtedly identical with the species as originally described and figured by Goeppert, but others are of doubtful identity, and none is as large as ours. A species that is, perhaps, more closely similar to ours, both in size and general appearance, is Platanus dissecta Lesquereux, from the late Tertiary (probably Miocene) of the western United States; and the only apparent difference between them is that ours are prevailingly larger in size and with a somewhat more divergent or spreading character in connection with the lateral lobes. Whatever may be thought of such surficial and minor differences as may be noted between the existing Platanus occidentalis and the three fossil forms P pseudoccidentalis, P. aceroides, and P. dissecta, it is apparent that their resemblance to each other is so close that in certain instances satisfactory differentiation would be difficult, if not impossible, and hence it would be hazardous to regard any specimen of the general type of Platanus leaf to which they belong as a safe index fossil in critical stratigraphic work. All that may be safely said in this connection, as far as our specimens described and figured under the name P. pseudoccidentalis are concerned, is that they are more suggestive of certain Tertiary species than they are of any Quaternary species thus far described or depicted. Incidentally, and for purposes of comparison, it may here be pertinent to call attention to two fossil leaves from the Pleistocene of the Don Valley, Toronto, Canada, that were described and figured by Penhallow, under the names Acer pleistocenicum and A. torontoniense. These leaves (see PLATE 47) I have reproduced, natural size, from photographs of the original specimens, kindly transmitted to me by Prof. J. H. White, of the University of Toronto. They represent the figures of the two species as originally depicted, reduced in size, by Penhallow, in the American Naturalist (loc. cit.). Our FIGURE 1 represents his single figure of A. pleistocenicum, and our FIGURE 2 the lower one of his two figures of A. torontoniense. The closer these specimens and photographs were studied, and the more extensively they were compared with species in the genera Acer and Platanus, the more certain it appeared that an error had been made in referring them to the former genus, and the more likely it appeared that their true generic relationship was with the latter. It may, indeed, be inferred that if Penhallow had not so referred them they would have been generally accepted as representing the genus Platanus and both, perhaps, merely as variant forms of P. occidentalis. The latter species was listed (loc. cit., American Naturalist, p. 448) as an element in the Pleistocene flora of the Don Valley and elsewhere, but no specimen recognized as referable to either Acer pleistocenicum or A. torontoniense has been recorded from any locality other than the Don Valley.

In the course of correspondence had with Professor White, in relation to the specimens from the Don Valley, he referred, under date of February 3, 1913, to the two species in question as follows: ". . . I find I cannot see eye to eye with Penhallow in some of his identifications. . . . Penhallow's list is peculiar in containing but two extinct species, Acer pleistocenicum and A. torontoniense. . . . I should prefer to call both the above Platanus."

In the circumstances I am inclined to regard the leaves that are included in these two species as representing a type of Platanus leaf that is characteristic of the Pleistocene of the Don Valley, and to utilize them for comparison with our much larger leaves from the Saint Eugene silts; and such comparison indicates that while the leaves from the two localities are apparently congeneric they must be regarded as specifically distinct and, apparently, each species representing a flora distinct from the other, either stratigraphic or regional.