Cercocarpus type




photo O.K.Davis



Cowania mexicana
UofAz 2405



Cowania mexicana
UofAz

Cercocarpus-Type: Several Rosaceous shrubs of western North America produce pollen that resembles that of oak (Quercus). These include Cercocarpus (mountain mahogany), Coleogyne (black brush), Cowania (cliff rose), and Purshia (bitter brush). This pollen type is often called "Cercocarpus-type," but the pollen morphology of the four types overlap among each other, and with Quercus.


Cercocarpus betuloides
UofAz 535

Cercocarpus betuloides
UofAz 535

Coleogyne ramosissima
UofAz 761

Coleogyne ramosissima
UofAz 761

Purshia tridentata
UofAz 1955

Purshia tridentata
UofAz 1955

Quercus arizonica
UofAz 8696

Quercus arizonica
UofAz 8696
 

Plants:
Cercocarpus (mountain mahogany) is a low tree (2 m) that is common in the chaparral zone of the Southwest, and in the upper woodland (pinyon-juniper) zone of the Great Basin and northward into western Montana. Purshia (bitter brush) is a shrub (1 m) characteristic of the sagebrush zone of western north America from Canada to the Mojave Desert. It is particularly abundant in the juniper woodlands of western California. Cowania (cliff rose) is a common shrub (1 m) of rocky areas of the grassland and lower woodland zone of the Southwest from northern Utah southward into Sonora. Coleogyne (black brush) is a common shrub (1 m) of the lower woodland zone and below of the transition from the Great Basin to the Mojave Desert.

Pollen light micrograph:
The pollen grains are tricol-(por)-ate, with the "pore" little more than an equatorial weakening of the furrow. Fossil grains of Cercocarpus-type pollen are typically bent mid-furrow, and constrictions or bulges (fresh pollen) may be evident in the pore areas. The furrows are "rose-like" with a distinct furrow boundary, particularly in the polar area. The furrows are typically wider than those of Quercus pollen. The furrow membrane is thin, and usually missing in fossil grains, but if present it may contain tectum fragments near the furrow margin, particularly near the equator. The sculpturing is generally finer than for Quercus, but some oaks have very fine sculpturing. No single character incontrovertibly distinguishes Cercocarpus from Quercus pollen.

Pollen scanning electron micrograph (SEM)
Striate-rugulate sculpturing is often apparent, which is rarely and inconsistently visible in light micrographs.

Production and Dispersal:
Low production, low to moderate dispersal. Seldome exceeding 10% of the upland pollen sum, but percentages as high as 30% have been recorded in stands of Cercocarpus ledifolius (Davis, 1995).

Preservation:
Moderately well preserved, about the same as oak.

Fossil Occurrence:
Late Quaternary of western U.S.A.

References:
    Davis, O.K. 1995.
    Climate and vegetation patterns in surface samples from arid western U.S.A.: Application to Holocene climatic reconstructions. Palynology. 19:97-120.

    Eide, F. 1981.
    Key for Northwest European Rosaceae pollen. Grana 20: 101-118.

    Reitsma, T. 1966.
    Pollen morphology of some European Rosaceae. Acta Botanica Neerl. 15: 290-307.

Links
Thomas A. Minckley suggested this as an interesting but problematic pollen type. He notes the presence of sculpturing elements on the margin of the furrow of pollen of the oaks of Northern California can be used to distinguish them from the Cercocarpus type. Thanks Tom!
Owen Davis 5/01