A New Species of Pinus Subgenus Pinus Subsection Contortae from Pliocene Sediments of Ch'ijee's Bluff, Yukon Territory, Canada

Abstract

Three structurally preserved conifer ovulate cones are described from Pliocene sediments at Ch'ijee's Bluff on the Porcupine River, near Old Crow, Yukon Territory, Canada. Cones are ovoid to conical, symmetrical, 3.4–4.4 cm long and 2.8–3.4 cm wide, with helically arranged cone‐scale complexes. Ovuliferous scales are thin at the base, expanded at the apex, 2 cm long and 1 cm wide, with flat, rhomboidal apophyses and minute dorsal umbos. Pith is parenchymatous with scattered sclerenchyma at its outer edge. The parenchymatous inner cortex contains 12–15 small resin canals. Outer cortex is also parenchymatous with a thin outer sclerenchymatous zone. Vascular tissues of the scale and bract originate as a complete cylindrical trace from the axis stele. Resin canals are abaxial to the scale trace as it separates from the bract. The abaxially concave ovuliferous scale trace splits into separate vascular bundles that alternate with resin canals in the most distal sections. Bracts separate from scales medially, lack abaxial lobes, and contain terete traces that are accompanied by two resin canals. The paired seeds are elliptical, 2.7–3.9 mm long and 2.1–2.5 mm wide, with wings up to 16 mm long. Fossils were compared anatomically with extant species of Pinus section Pinus. The fossil cones most closely resemble those of Pinus contorta Dougl. ex Loud. but differ from any previously described fossils of this species or extant subspecies by a combination of cone characters. The symmetrical cone shape, nonreflexed cone base, flattened apophyses, cone serotiny, and seed wing length distinguish these cones from P. contorta. These cones are described in a new species of Pinus subgenus Pinus Subsection Contortae, Pinus matthewsii sp. nov. Like P. contorta, P. matthewsii may have been a colonizer of open habitats. The scarcity of these fossil cones, the presence of numerous cones of Picea Dietr. and a Pinus monticola–like species and abundant Picea, Pinus, and Betula pollen indicate dense forest cover dominated by spruce, soft pines, and birch.