Pseudotsuga, Larix (Pinaceae)


Pseudotsuga menziesii L.Brubaker
Conifer Database C.Earle

Pseudotsuga menziesii LM
Pseudotsuga menziesiiAZ 486 N.Bader (folded)
UofAz Palynology

Pseudotsuga menziesii
Pseudotsuga menziesii SEM C.Drew (collapsed)
UofAz Palynology

Plant:
Douglas fir (Pseudotsuga) is a common mid-elevation coniferous tree of western North America, and several other species in eastern Asia. The needles are flat, 1.5 - 3 cm, with narrow peteoles. The cones are 8 - 12 cm, with thin scales, and protruding bracts.

Larches (Larix) are deciduous coniferous trees widespread throughout the boreal region of the northern Hemisphere. Thin, short needles are produced seasonally on short side branches. Cones are small (2 - 5 cm), with protruding bracts.

Pollen light micrograph:
Pseudotsuga menziesii Pollen spherical, inaperturate, psilate. Pseudotsuga (Douglas fir) pollen ranges from 90 to 100 µm and Larix (Larch) pollen is smaller -- from 70 to 100 µm. Both appear smooth in light micrographs, but have an uneven texture under SEM. Occasional tri-radiate ridges, can be seen on both types of pollen, presumably formed while the grains are in tetrads. Although inaperturate, the Pseudotsuga - Larix pollen type is easily distinguished from the inaperturate Juniperus pollen type by its much larger (70 - 100 µm) size and smooth sculpture. (The Juniperus type is 20 - 35 µm, with gemmate sculpture) However, both types of pollen grains split to form "pac man" shapes (illustration, right), which likely speeds their deterioration following sedimentation.

Pollen scanning electron micrograph (SEM)
Sculpturing of the spherical grains is rough.

Production and Dispersal:
Pseudotsuga and Larix pollen grains are very poorly dispersed and occur in small numbers, and only near to the plants which produce them.

Preservation:
The absence of an aperture and consequent splitting of the pollen grain may speed the grain's deterioration.

Fossil Occurrence:
Douglas-fir plant fossils have been found in both Asia and western North America from Oligocene onward. Neither Pseudotsuga nor Larix pollen is common in the fossil record.

References:
Links

Owen K. Davis 12/99