Tsuga heterophylla and T. canadensis (Pinaceae)


Tsuga heterophylla L.Brubaker
Gymnosperm Database, C.Earl

Tsuga canadensis
Tsuga canadensis Kapp's 1969
UofAz Palynology


Tsuga canadensis
Museum Univ. Nebraska Lincoln

Plant:
Trees with yellow-brown hairy twigs. Leaves rounded, 1-2 cm, with 2 white stomatal bands beneath. Female cones ovoid, 2.5cm. Tsuga canadensis in eastern Canada and USA east of the Mississippi, T. caroliniana in the USA Southeast, T. heterophylla in western Canada and Pacific Northwest of USA.

Pollen light micrograph:
The morphology of the Tsuga heterophylla type is unique, and the beginning palynologist might be surprised that it is classified as "saccate" or "vesiculate" pollen, because it is so different from the bisaccate pollen of other Pinaceae. However, the encircling "frill" or "fringe" is homologous with the paired sacci of pine, spruce, and fir. And, its rough - undulating sculpturing is similar to the anti-saccus surface of those grains. To me, the frill is reminiscent of a medieval monk's tonsure.
The morphology of Tsuga canadensis is very similar to T. heterophylla. It is 70 to 80 µm in diameter and is essentially spherical. However, the mountain hemlock (Tsuga mertensiana) of western North America is small and bissacate. There are several species of Asian hemlocks. Tsuga forrestii is illustrated in Erdtman (1957) as both monosaccate and bisaccate, but T. chinensis, T. diversifolia, T. dumosa, T. pattoniana, T. sieboldii, and T. yunnanensis are not descirbed in that text.

Pollen scanning electron micrograph (SEM)

Production and Dispersal:
Wind pollinated with moderate production moderate dispersal

Preservation:
Well preserved.

Fossil Occurrence:
An abrupt decline in the abouncance of eastern hemlock (T. canadensis) occurred 4700 years ago, possibly due to the spread of a pathogen.

References:
    Erdtman, G. 1957.
    Pollen and Spore Morphology / Plant Taxonomy. Gymnospermae, Pteridophyta
    Bryophyta. Almqvist abd Wiksell. Stockholm.

    Kapp, R.O. 1969.
    How to know pollen and spores. W. C. Brown Co. Publ. Dubuque, Iowa. 249 p.

Links

Owen K. Davis 12/99