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