A preliminary discussion of fossil larches ( Larix, pinaceae) from the arctic

Abstract

Structurally preserved three-dimensional cones of Larix Miller occur in later Tertiary (mid-Pliocene?) beds at Ch'ijee's Bluff, Unit 1 (Twelvemile Bluff) near Old Crow, Yukon, Canada. The morphology of these cones is compared to herbarium material and previously described and illustrated fossil cones, and they are considered part of the extant L. decidua-gmelinii alliance. The systematic relationships of the extant and fossil taxa are reviewed and a new system of classification proposes a partitioning of Larix into two groups on the basis of bract scale morphology. Group I (‘Aristatus’) Larix retain the inferred primitive bract type shared with Pseudotsuga; a relatively long-exserted, tridentate bract in which the costa of the medial fork extends well beyond the lateral forks as a relatively long aristate projection. Group II (‘Laminatus’) Larix includes those forms in which the aristate costa is reduced and all three forks of the tridentate apex are similar in size and shape. In the ‘Laminatus’ group, the overall trend is toward reduction in bract size. Fossil cones from Poland to Greenland, ranging in age from Eocene to Pleistocene, share very similar morphologies which characterize Group II (‘Laminatus’), subgroup IIb. Subgroup IIb includes the forms of Larix with short bracts that are typically hidden beneath the closed, overlapping cone scales. Partitioning the suite of similar Group IIb fossils must await a detailed morphometric-statistical-anatomical analysis. The modern widespread boreal and more restricted European species have their origins in the later Tertiary Group IIb complex.